# Wikijunior:Solar System/Solar System

{{  }} !The Hubble Space Telescope. This
telescope is in space. It takes pictures of things that are too far away
to be seen with a regular
telescope.
Do you ever wonder about the things in the sky---the Sun, the Moon, the
stars? People have been watching the sky for a long time, trying to
figure out what is out there. We keep coming up with new ways to learn
more about outer space.

*Planets* are big balls of rock or gas that move around stars. We live
on one we call the Earth, which moves around a star we call the Sun.
There are at least seven other planets moving around the Sun and a lot
of other smaller things as well. All these things together are called a
*system*. The Latin word for the Sun is *Sol*, so we call this system
the *Solar System*. Far beyond our own Solar System are stars, bodies
like the Sun but in some cases much bigger.

!The eight planets of the Solar System, and the sun. Sizes are to
scale, but distances are
not.{width="180"
height="200"} Thousands of years ago, a man named **Aristarchus** said
that the Solar System moved around the Sun. Some people thought he was
right, but many people believed the opposite: that the Solar System
moved around the Earth, including the Sun (and even the other stars).
This seems sensible because the Earth doesn\'t feel as if it\'s moving,
does it?About 500 years ago, another man named **Copernicus** said the
same thing as Aristarchus: that all the planets moved around the Sun and
the stars were fixed in space.[^1] This time, more people agreed, but
there were still people who thought the opposite. Then, about 100 years
later, a man called **Galileo Galilei** began looking at the sky with a
new invention: the telescope. He showed that it was very likely that all
the planets moved around the Sun. This time, even more people thought
Galileo may be right and that the Earth really did move around the Sun.
Soon, more and more people started using telescopes to study the sky.
However, there were still some people who thought Galileo was wrong, and
he was even arrested and taken to court for lying. All the people who
believed him began to learn how the planets and the other things in the
Solar System moved so they could prove that he was not lying. Thousands
of years after Aristarchus, people finally said \"Okay, the Earth does
move around the Sun\". Galileo couldn\'t be called a liar anymore.[^2]

We can use very large telescopes to see what has happened to other
stars. We can compare pictures of distant stars with pictures of our own
star, the Sun. We live in exciting times because, for the first time, we
have sent people into space, and we also have telescopes in space. These
telescopes in space take thousands of pictures of the planets, our sun,
and the distant stars. On Earth, people use the photos to learn about
all the different things in the Solar System and they try to explain how
the Solar System began. We even have a robot on the red planet Mars that
moves around, and people on Earth tell it where to go and what to
photograph. We also want to know what will happen to the Earth and the
Solar System in the future.

## What is in the Solar System?

!The Solar System, showing the Sun, inner planets, asteroid belt, outer
planets, an outer dwarf planet, and a comet. (Not to
scale!)"){width="250"}
At the center of the Solar System is the Sun. It is a star, like the
billions of other stars in the sky. The other stars are very, very far
away, so they look tiny. The Sun is important to us because it gives us
heat and energy that allows life. None of the life on Earth could exist
without the Sun.[^3]

The rest of the things in the Solar System *orbit* (travel around) the
Sun. The planets are the largest of these. Each planet is a little like
the Earth. But the planets are also very different from each other.

Many of the planets have *moons*. A moon orbits a planet. Mercury has no
moons,[^4] and neither does Venus. Earth has one. Saturn has more than
80![^5]

The planets closest to the Sun are called the *inner planets*. These are
Mercury, Venus, Earth, and Mars. Then comes a big ring of *asteroids*,
chunks of rock much smaller than planets. This ring is called the
*asteroid belt*. Within the asteroid belt, there is a dwarf planet
(smaller than a normal planet) named Ceres. Then come the *outer
planets*: Jupiter, Saturn, Uranus, and Neptune. Farther out there are
two dwarf planets, Pluto and Eris.

The planets have the names of Roman gods that were worshipped by people
thousands of years ago, though no one believes in them now. Did you know
that some days of the week are also the names of ancient gods? Saturday
means \"Saturn Day\". Thursday means \"Thor Day\". Thor was a Viking god
and the son of Odin. Monday and Sunday simply mean \"Moon Day\" and
\"Sun Day\". Some of the months are also named after Roman gods. The
month of \"March\" is named after the Roman god \"Mars\"---he was the
god of War!

Beyond the orbit of Neptune is another big ring of things like the
asteroids, called the *Kuiper belt*. Kuiper (said \"KYE-per\") was the
last name of the person who first wrote about it. Most of the things in
the Kuiper belt are hard to see through telescopes.

After the Kuiper belt comes the *Oort cloud*. Scientists think this is
where *comets* come from. It is very far away, many times farther away
than Pluto is from the Sun (over a thousand times). It is near the edge
of the Solar System.[^6] (Yes, \"Oort\" was the last name of the person
who first wrote about it.)

!Zodiacal
light.{width="200"
height="200"} In between all the other things is dust. The pieces of
dust are very far apart, but they shine in the light of the Sun. Before
dawn, in September or October, they glow in the East. We call this the
*zodiacal glow* or *zodiacal light*.[^7]

When pieces of space dust hit the Earth\'s atmosphere, they burn
brightly. We call them shooting stars or meteors.

The Sun creates *solar wind*---a kind of gas that blows away from the
Sun into space. This gas travels out past the planets into outer space.
The edge, where the solar wind meets the wind from other stars, is
called the *heliopause*. That is about 100 times as far from us as the
Earth is from the Sun.[^8] Beyond that, there is a lot of empty space.
The nearest star to our Sun is thousands of times farther away than the
size of the entire solar system. The Universe is a really huge and empty
place![^9]

### What holds it together?

!Sir Isaac Newton, the discoverer of gravity. It is said that he came
up with the concept of gravity when an apple fell on his
head..jpg "Sir Isaac Newton, the discoverer of gravity. It is said that he came up with the concept of gravity when an apple fell on his head."){width="200"
height="220"} Why do all of the planets orbit the Sun? Why do moons
orbit planets? Why doesn\'t the Sun move away and leave the planets
behind? The answer to all of these questions has to do with *gravity*.
Gravity is a force that is a property of *mass*. It pulls things
together.

We don\'t notice the pull from the Sun because it also pulls on the
Earth by the same amount. But the Sun\'s gravity is strong enough to
keep the Earth from shooting away. Even though the Earth is going fast,
it keeps turning to go around the Sun. It is like they were tied
together with an invisible string. In the same way, moons orbit many of
the planets. They are kept there by gravity. The Sun itself does not sit
still in space. The entire Solar System orbits the center of our galaxy.
The whole thing stays together because of the force of gravity[^10].

#### About mass

Everything is made of matter. The amount of matter is called mass. Two
apples have twice the mass of one apple. The more mass a thing has, the
more gravity pulls it, and the more its gravity pulls other objects. We
don\'t notice the pull from an apple because it is so much less than the
pull from the Earth. If you stand on the ground and let go of an apple,
gravity will pull it down towards the center of the Earth. It will hit
the ground. If you could throw the apple hard enough at the right angle,
it would go into orbit around the Earth. That is how rockets put
astronauts into orbit. If you threw the apple really, REALLY hard in the
right direction, it would fly away from Earth and never come back, but
our arms are not that strong.

The force of gravity from anything is strongest when very close to that
thing and weaker when further from it. Scientists use *weight* to mean
how hard gravity pulls us. Astronauts weigh less on the moon because it
has less mass. It does not pull as hard. We actually weigh a tiny bit
less on top of a tall mountain than we do in a lower place. This is
because we are farther from most of the Earth.[^11]

## Who discovered the Solar System?

Anyone who looks up at the sky enough can see seven bright objects.
These are the Sun, our Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
People have known about them for a very long time. Ancient people
thought they were related to gods. In Babylon, they named the days of
the week after them. Almost everyone was sure that all these things were
orbiting the Earth. They did not know we lived in a **Solar** System.

In about 1500, Nicolaus Copernicus figured out that the planets orbit
the Sun. Only the Moon orbits the Earth. But he was afraid to say so for
most of his life and only published a full account of his ideas in 1543,
the year of his death.[^12] Then Galileo Galilei pointed a telescope at
the sky. He found moons orbiting Jupiter. He was certain Copernicus was
right, and he got in trouble for saying so. It took seventy years to
convince scientists that the planets orbit the Sun.[^13] Now, almost
everyone on Earth understands that we live in a Solar System. !The
largest objects at the farthest reaches of the Solar System, even
farther than
Neptune!{width="200"
height="200"} People made better telescopes and found more things in the
sky---moons,[^14] new planets,[^15] and asteroids.[^16] More things,
like the dwarf planet Eris, are being found today.[^17]

## How have we explored the Solar System?

!The *Voyager 2*
spacecraft.{width="250"}
!An artist\'s impressions of
*Spirit*.{width="250"}
Before the telescope , people explored the sky with their eyes. They saw
how the planets seemed to \"wander\" through the sky. They learned to
predict where the Sun, the moon, and planets would be in the sky. They
built some *observatories---*places for watching the sky. *Observe* is a
more scientific word for *watch*. They observed the Sun and stars to
tell the time of year. In China, they even knew when the moon would
block the Sun[^18]. Most people thought that *celestial bodies* could
cause war or peace on Earth.[^19]

After telescopes were first made in the early 17th century, people kept
making them better. Astronomers saw that planets are not like stars.
They are worlds, like the Earth. They could see that some planets have
moons.[^20] They began to think about what these worlds were like. At
first, some thought that the other planets and moons had people or
animals living on them. They thought about how it would be to live on
these other worlds.[^21] Then they made telescopes better and sent
spacecraft into space, and found that there were no plants or animals on
the Moon[^22] or on Mars.[^23]

Now, we can explore by going to some of the other worlds. Twelve
Astronauts walked on the Moon about 35 years ago. They brought rocks and
dirt back to Earth.[^24] Spacecraft flew by Venus, Mars, and the outer
planets. The pictures they took showed us a lot of what we know about
these worlds.[^25] Robots landed on Mars in 1971, 1976, and 1997. They
took thousands of pictures of the planets. They send photos and movies
back to Earth. They also check rocks to find out what they are made
of.[^26]

So far, we have not found any life except on Earth. Maybe tiny,
one-celled life once lived on Mars. Maybe there is life under the ice on
Jupiter\'s moon Europa. New spacecraft are being planned to look for
life on these worlds.[^27]

## How was our Solar System formed?

Our Solar System is part of the Milky Way *galaxy*. Galaxies are big
mixes of dust, gas, stars, and other things. Inside our Milky Way galaxy
are clouds of dust and gas where stars are born. Our Solar System was
created in this kind of cloud. A part of the cloud began to get smaller
and less spread out. It formed a big, spinning disk of gas and tiny
pieces of dust. This disk was thickest in the middle. The middle slowly
collapsed until it became the Sun. We are still trying to learn how the
planets were formed. Most scientists think that they were formed from
leftover gas and dust.

200x200px\|framed\|left\|An artist\'s illlustration of how the Solar
System began. This is how it
could have happened. The rest of the disk continued to spin around the
Sun. The tiny pieces of dust hit each other, and some of them stuck
together. Next, the bits of dust slowly collected to form grains, which
in turn joined to form lumps the size of gravel, then pebbles, and then
rocks. The rocks crashed together into mountains. The mountains crashed
together to make bigger things. These big things swept up most of the
rest of the disk to form the planets, moons, and asteroids.[^28]

The Sun got hotter as it collapsed. It began to glow. The temperature at
the center reached a million degrees Celsius. The Sun started to produce
a lot of light and heat. This light and heat swept away most of the
leftover dust and gas between the inner planets. This light and heat are
the sunlight we see and feel every day on Earth. [^29]

## What will happen to the Solar System?

In another five billion years, the Sun will use up most of its hydrogen
fuel. It will enter the final stages of its life. The middle of the Sun
will shrink down and become even hotter. The outer layer of the Sun will
grow much bigger than it is now. It will form a *red giant*.

It will be so big that Mercury and Venus, probably Earth and maybe even
Mars will be inside it. These planets will burn away. Which planets get
destroyed will depend on how much mass the Sun has left.[^30] A strong
solar wind will blow some of the outer layers of gas away from the Sun.
The Sun will have less mass. The Sun's gravity will be less. All of the
planets will move further away from the Sun.[^31]

!The massive, rapidly-aging star *Eta Carinae* throws off a giant cloud
of gas, forming a *planetary
nebula*.{width="250"}

After it has been a red giant for a while, the Sun will start to burn
*helium*. It will shrink down and will not be a red giant any more. It
will use the helium up in about a billion years. Then it will become a
red giant once again. More gas will blow away for a few hundred thousand
years.

A *planetary nebula*[^32] will form. The nebula could last for a few
thousand to a few tens of thousands of years. It will glow in the light
of the Sun.[^33]

At the center, the Sun might shrink into a tiny star called a **white
dwarf**. That kind of star is about the size of Earth. It would take
about 100 of these white dwarfs, stacked end to end, to be as wide as
the Sun is today. The Sun will not have any more fuel to burn. It will
have lots of heat left over and will keep getting cooler and dimmer.
Then its light will go out in a hundred billion years from now.[^34]

Next Topic: The Sun

## Notes

```{=html}
<div style="clear:both;">
```
```{=html}
</div>
```
## References

bs:Wiki junior Sunčev sistem/Sunčev
sistem
bg:Уикиджуниър Слънчева система/Слънчева
система
de:Wikijunior
Sonnensystem/\_Sonnensystem
es:Wikichicos Sistema Solar
fr:Wikijunior:Système
solaire fi:Wikijunior
Aurinkokunta it:Wikijunior Il
sistema solare

[^1]: <http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#q21>

[^2]: <http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#galileo>\
    See also
    \

[^3]: <http://imagine.gsfc.nasa.gov/docs/science/know_l1/sun.html>

[^4]: <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mercury&Display=Moons>

[^5]: <https://solarsystem.nasa.gov/moons/saturn-moons/overview/?page=0&per_page=40&order=name+asc&search=&placeholder=Enter+moon+name&condition_1=38%3Aparent_id&condition_2=moon%3Abody_type%3Ailike>

[^6]: <http://solarsystem.nasa.gov/index.cfm>

[^7]: <http://www.gsfc.nasa.gov/scienceques2001/20020301.htm>

[^8]: <http://antwrp.gsfc.nasa.gov/apod/ap020624.html>

[^9]: \"Outside Our Solar System\" in
    <http://vathena.arc.nasa.gov/curric/space/spacover.html>

[^10]: \"Gravity is the force responsible for keeping the Earth and
    other planets in our solar system in orbit around the Sun.\" from
    Cosmic Glue,
    <http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970108b.html>

[^11]: Definitions of Mass, Gravity, and Weight from
    <http://ksnn.larc.nasa.gov/webtext.cfm?unit=float>

[^12]: <http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#q21>

[^13]: <http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#galileo>

[^14]: Calinger, Ronald S. \"Huygens, Christiaan.\" World Book Online
    Reference Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar268300>.;\
    <http://www.nasa.gov/worldbook/huygens_worldbook.html>

[^15]: <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Uranus>

[^16]: <http://solarsystem.nasa.gov/planetselector.cfm?Object=Asteroids>

[^17]: <http://www.space.com/scienceastronomy/050729_new_planet.html>;\
    <http://science.nasa.gov/headlines/y2005/29jul_planetx.xml>;\
    <http://www.jpl.nasa.gov/news/news.cfm?release=2005-126>

[^18]: Eclipse2001 museum <http://museumeclipse.org/about/history.html>

[^19]:
        \
    page 339 \"The Chaldeans \... were also the first to suspect\...
    that the Sun, the moon, the planets and the constellation of stars,
    all affect human life and destiny\.... These beliefs gradually
    spread .. to Egypt, China, Greece, India, and Rome, for example \...
    astrology is still very popular.\"

[^20]: <http://www-spof.gsfc.nasa.gov/stargaze/Ssolsys.htm#galileo>

[^21]: <http://vesuvius.jsc.nasa.gov/er/seh/mars.html>;\
    ;\
    ;\
    From the Earth to the Moon on Project Gutenberg \--
    <http://www.gutenberg.org/etext/83>;

[^22]: <http://www.space.com/reference/mars/history.html>

[^23]: <http://www.hq.nasa.gov/office/pao/History/SP-350/ch-15-4.html>
    (bottom of page)

[^24]: <http://spaceflight.nasa.gov/history/apollo/index.html>

[^25]: <http://www.solarviews.com/eng/sc_hist.htm>

[^26]: <http://marsrovers.jpl.nasa.gov/home/>

[^27]: <http://www.nasa.gov/missions/solarsystem/Why_We_12.html>;
    <http://www.infoplease.com/spot/astronomy1.html>

[^28]: <http://planetquest.jpl.nasa.gov/science/origins.html>

[^29]: <http://rst.gsfc.nasa.gov/Sect19/Sect19_2a.html>

[^30]: Which planets may get destroyed
    <http://www.public.iastate.edu/~lwillson/FuturSun.pdf>

[^31]: Outline of Sun\'s death
    <http://www-astronomy.mps.ohio-state.edu/~pogge/Lectures/vistas97.html>

[^32]: A *planetary* nebula was named this because through the earliest
    telescopes, astronomers thought that they looked like planets. The
    name stuck --- but they really have nothing to do with planets.

[^33]: Planetary nebulae <http://www.seds.org/messier/planetar.html>

[^34]: Has information on white dwarf stars
    <http://math.ucr.edu/home/baez/RelWWW/tests.html>


# Wikijunior:Solar System/The Sun

## What is the Sun?

{{/Coolfacts\|=
1\|!☉.svg "☉"){width="80"}\|= 2\|Sun Facts\
WARNING: Never look directly at the Sun; it can hurt and damage your
eyes.\|= 3\|

-   If you looked at the Sun in a telescope, you could risk blindness.
-   The Sun is 150,000,000 km (93 million miles) away from Earth.
-   The Sun\'s light takes 8 minutes to reach us on Earth. That means
    that if the Sun blew up, we wouldn\'t see it blow up until 8 minutes
    later!
-   Every second, the Sun turns over 4 million metric tons of gas into
    energy. That\'s 881,849,000,000 pounds!
-   The Sun is as wide as 109 Earths.

}} The Sun is a star --- the closest star to Earth. It is a large ball
of very hot gas in a (plasma) state. The air we breathe and the helium
in a balloon are both gases. It is over 5,500 °C at the surface, and
much hotter at the center, about 15 million °C. The Sun is made of
mostly hydrogen (70%) and helium (28%). It turns many tons of hydrogen
into helium every second, thus creating heat and light.

The Sun makes light and heat that warms the surface of the Earth and
allows plants to grow. We can get food from plants, and we can burn wood
and other parts of plants to cook, warm our houses, and make cars go.
Without the Sun there could not be any life on Earth.

### How big is the Sun?

The Sun is very big --- much, MUCH bigger than the Earth! Even the
mighty planet Jupiter is small by comparison. It is more than a million
km (109 Earths) across and contains about 99.86% of the Solar System\'s
mass. If you could stand on the surface of the Sun, you would weigh 28
times as much as you do on Earth because the Sun has more mass and
therefore more gravitational pull than earth.

More than a million Earths could fit beneath the surface of the Sun. It
doesn\'t look that big from Earth, though. That\'s because the Sun is so
far away. Compared to other stars, the Sun is about average-sized. There
are much bigger stars, and much smaller stars.

A very thin *solar wind* of charged particles blows from the Sun all the
way to the edge of the Solar System. When it gets there, the gases mix
with those coming from other stars.

### What is the surface like?

The Sun doesn\'t have a crust like the Earth that you can stand on. The
whole Sun is made out of gases, fire, and plasma. The gas becomes
thinner as you go farther from the center of the Sun. The outer-part we
see when we look at the Sun is called the photosphere, which means
\"ball of light\". We call it the surface of the Sun because that\'s
where most of the light we see comes from. There is actually a lot of
material from the Sun above the photosphere, and some of the gas is even
blasted away to great distances.

## How does the sun make light and heat?

The Sun is the main source of energy for the Earth. This energy is made
deep inside the Sun in a process called *nuclear fusion*. Four hydrogen
`<b>`{=html}atoms`</b>`{=html} are fused together to make one helium
atom. Some of the leftover matter turns into energy. This is the same
way energy is released in a hydrogen bomb.\
{{  }}

upright=1.5\|thumb\|What is going inside the Sun. The different colors
show the different regions.

**Core**: The center of the Sun is very dense. It\'s about 12 times as
dense as lead. That means that a gallon of the gas from the core of the
Sun would weigh half a ton. It\'s also very hot --- about 15,000,000 °C.
This region is where most of the nuclear reactions are taking place.

**Radiative zone**: In this zone the light and heat produced in the core
fight their way out towards the surface. The gases that make up the zone
are very dense and keep absorbing and emitting the rays. Have you ever
tried to run through water? That\'s what it\'s like for light waves in
this region of the Sun. Light can\'t go very far at all before it runs
into something. Then it bounces off in a different direction. The light
doesn\'t get very far this way. It can take a single ray of light a
million years to get out of this zone.

**Convection zone**: Have you ever seen the air shimmer above a fire?
Perhaps you\'ve been told it\'s because heat rises? Actually, it is the
hot air that is rising. Hot gases get less dense and rise. Cold gases
get denser and sink. In this zone, the gases are less dense. They behave
like air in a fireplace. Gas at the bottom of the zone gets heated up
from below. It rises to the surface, gives off its heat to space, and
sinks again. The gas in the convection zone forms currents like those in
Earth's oceans and atmosphere. The currents are called *convection
cells*.

## What are sunspots?

!The dark areas are
sunspots Sunspots are dark
spots on the Sun, but they are still brighter than lightning. Sunspots
look darker than the rest of the Sun because they are a little cooler.
Even though sunspots are cooler than the rest of the Sun, they are still
hot --- about 4000 °C (7000 °F). Sunspots are caused by changes in the
Sun's magnetic field. The magnetic field stops convection, which causes
the sunspot areas to cool off and become darker. Sunspots usually form
in groups which are carried around the Sun as it rotates.

The number of sunspots we see goes up and down in a cycle of average
length about 11 years.

## What is the Solar Atmosphere like?

Above the photosphere, the Sun's gases are not very dense at all. There
are two layers that we can see with special telescopes. Above that,
gases stream out as *solar wind* that reaches to the edge of the Solar
System.

left\|thumb\|A closeup view of a sunspot and
prominences

### Prominences and solar flares

If you have a telescope with special filters, you can see bumps around
the edge of the Sun. Each one of these is called a *prominence*. They
look like volcanoes erupting. They are hundreds or thousands of
kilometers long. Some are bigger than the Earth. They often seem to come
from sunspots. Sometimes they get so far away from the Sun that they fly
away from it. Then they are called *solar flares*.

### Chromosphere

*Chromosphere* means \"color ball\". It is just above the photosphere.
It is not as bright as the photosphere, and you can\'t normally see it.
But you can see it just before a solar eclipse (only with special
filters!). It looks like a flash of all the colors of light.
Surprisingly, the Chromosphere is even hotter than the photosphere, at
some parts over 20,000 °C.

### Corona

!The Sun\'s corona during an
eclipse
*Corona* means \"crown.\" That is what pictures of the corona look like.
It is just above the chromosphere. It is hotter than the photosphere,
and it glows. It is made of thin gases, and blows away as solar wind. It
shifts and changes, but it is hard to see, even with special telescopes.

### Solar wind

At the top of the corona, some of the gas blows out as solar wind. It
blows fast --- about 60 km per second (more than 100,000 miles per
hour). But there isn\'t very much of it. The solar wind is strong enough
to push dust and gas away from a comet to make a tail.

The solar wind can even push big things. In 1960, the satellite Echo I
was put into orbit. It was a large balloon. Since it was so large and
light, the solar wind pushed it around in its orbit. In the future, some
space craft may use the solar wind to travel between planets using
*solar sails* similar to the way sailboats use the Earth\'s wind in
their sails to cross the ocean.

### Heliopause

thumb\|left\|Heliopause: where the solar wind hits the edge of the
Solar System *Heliopause*
is where the solar wind hits the wind from other stars. Near here, the
solar wind slows down suddenly. In May 2005, the Voyager I spacecraft
went through this region and felt a big bump. It is now just inside the
heliopause. Because this happens so far from Earth, it is hard to
study!\

## What is solar weather?

Did you know the Sun has weather? Earth weather is what is going on in
Earth's atmosphere. *Solar weather* is what\'s going on in the Sun's
atmosphere. Solar weather affects us on Earth. Solar weather (also
called space weather) includes sunlight and the solar wind.

Solar flares shoot a lot of very hot gas out from the Sun. If a solar
flare is aimed towards Earth, protons --- subatomic particles with
positive electric charge --- might be shot at Earth at high speed, and a
*solar storm* could result. That could cause electrical blackouts or
block radio signals. It could damage satellites in orbit. Radiation from
a bad solar storm could be very dangerous for astronauts, so they must
be protected. The Earth's magnetic field and atmosphere usually protect
us from flares.

!Northern Lights Solar flares
can also cause an *aurora*. Auroras look like beautiful curtains of
shimmering light. They are called Northern Lights (Aurora Borealis) if
they are near the North Pole. They are called Southern Lights (Aurora
Australis) if they are near the South Pole. Solar weather affects other
planets, too. We have pictures of auroras on every planet except Mercury
and Pluto.

Just like we can get Earth weather forecasts, we can get Solar weather
forecasts. Forecasters study the Sun to figure out when flares will
happen. They try to tell when solar storms will hit Earth. They also try
to tell when solar storms will go to other parts of the Solar System.

Next Topic: Mercury

## The life cycle of a star

upright=3\|thumb\|center\|Life Cycle Of Our
Sun A forming sun\'s life starts
out as a nebula; this is a cloud of gas made up mostly of hydrogen. Over
time the nebula contracts; its core becomes more and more compact and
hotter until it can fuse hydrogen to helium. This fusion becomes its
power source. After this, the star will look very much like our sun.
They fuse hydrogen atoms together to make helium atoms.

!A comparison between the sizes of the Sun as it is now, and how it
will be as a red
giant.

After billions of years, this star will die. The star will exhaust its
supply of hydrogen in its core, so that there will no longer be any
source of heat to support the core against gravity. The core shrinks,
and the hydrogen starts to burn in a shell around the core. The outer
layers of the star swell and cool, creating a red giant. This is all
with an ordinary star and will be the life cycle of our sun, although
the process may vary from star to star. When our sun becomes a red giant
it will consume Mercury and Venus, and possibly the Earth. The sun will
then begin a cycle of expansion and contraction, puffing away its outer
atmosphere as the solar system becomes a planetary nebula. Once the sun
can not longer sustain fusion, it will collapse down and condense into a
white dwarf star. At this stage the light it emits is the left over
energy of our dead sun, radiating the residual heat until eventually the
white dwarf cools and darkens.

## Exploration of the Sun

Early space probes designed to collect information about the sun were
NASA\'s Pioneers 5 through 9 and the Helios 1 and 2. Those were in the
1950s, 60s, and 70s. They collected a lot of data about the Sun. Other
projects observed the Sun from Earth orbit, such as a Japanese satellite
launched in 1991 called Yohkoh, which means *Sunbeam* in English. It
told scientists more about solar flares, and activity on the sun\'s
surface. Thanks to Yohkoh, they knew more about how to classify solar
flares, and whether or not they will cause electrical disturbance on
Earth or not. Two important missions to study Sun are called the *Solar
and Heliospheric Observatory* (SHO) and the *Solar Dynamics Observatory*
(SDO). They have taken many pictures of the Sun, along with discovering
many comets near the Sun. All of these observations were across the
Sun\'s equator. The first space probe to observe the Sun\'s poles was
named *Ulysses*, after a famous Greek king who traveled on a very, very
long voyage. The Ulysses probe went all the way to Jupiter before
approaching the Sun. It took a famous picture of the comet
*Shoemaker-Levy-9* colliding with Jupiter.

!The Shoemaker-Levy 9 fragments falling back on
Jupiter.

## References

NASA. The Chromosphere ---
1\
Col, Jeananda. Enchanted Learning/Zoom Astronomy
2
1998--2005\
`<i>`{=html}Usborne Internet-Linked Science Encyclopedia`</i>`{=html},
Usborne Publishing Ltd.
3\
Dickinson, Terrence. `<i>`{=html}The Universe and Beyond`</i>`{=html} .
Firefly Books \
ar:ويكي الأطفال:نظام
شمسي/الشمس bs:Wiki junior
Sunčev sistem/Sunce
de:Wikijunior
Sonnensystem/\_Die_Sonne
es:Wikichicos Sistema Solar/El
Sol
nl:Wikijunior:Zonnestelsel/Zon
zh:Wikijunior:太阳系/太阳
fr:Wikijunior:Système solaire/Le
soleil


# Wikijunior:Solar System/Mercury

!Mercury from the MESSENGER
spacecraft.
\_\_TOC\_\_ {{-}}

## What is Mercury?

{{/Coolfacts\|!☿.svg "☿"){width="80"}\|*Mercury
Facts*\|

-   Mercury orbits around the Sun faster than any other planet.
-   Mercury\'s surface temperature can vary from -180°C (-300°F) to
    430°C (800°F). On Earth, the hottest temperature was recorded at
    58°C (136°F).
-   There may be ice on the top and bottom of Mercury.
-   Mercury is the smallest planet in the solar system.
-   The ancient Romans named a day of the week after the planet Mercury;
    even today, in French Wednesday is *Mercredi*, in Spanish
    *Miércoles*.

}}

Mercury is the closest planet to the Sun. It is a *terrestrial planet*;
that means a planet made from rock like Earth. It does not have a gas
atmosphere, so there is no weather. For a long time, only one
spacecraft, Mariner 10, had visited Mercury. In January 2008, the
MESSENGER spacecraft went by Mercury. It has gone by Mercury two more
times, and has started to go around the planet in 2011.

## How big is Mercury?

!Comparison of the size of Mercury to the
Earth
Mercury is 4879 km across. Mercury\'s diameter is just less than half
the diameter of the Earth. It is the smallest planet in the Solar
System. Only dwarf planets like Pluto are smaller. Because Mercury is
much closer to the Sun than the Earth, it can only be seen just after
the sun goes down at night or shortly before it rises in the morning.\

## What is Mercury\'s surface like?

!View of the surface of
Mercury Mercury has
craters like those on the Earth\'s moon. The largest crater on Mercury
is the *Caloris Basin*. It is about 1300 km wide. It was created by a
huge asteroid hitting Mercury. The asteroid was probably 100 km wide,
but it hit Mercury\'s surface so hard that it made a much bigger hole.

{{  }} The surface also has big cliffs
called *scarps*. They were made long ago when Mercury cooled down. It
shrank, causing the surface to get wrinkled in some places. This
wrinkling created the scarps.

There may also be ice on the top and bottom of Mercury. Like the Earth,
these areas (called *poles*) don\'t get much warmth from the Sun. Any
ice there won\'t melt.

It is very hot during the day (over 400°C) because Mercury is so close
to the Sun. At night it is very cold because Mercury loses almost all
its heat since there is almost no *atmosphere* to keep the warmth there.
The temperature can fall to almost -175°C.

## How long is a day on this planet?

Mercury *rotates* (spins around) much more slowly than the Earth. It
takes Mercury 58 days to spin once as viewed from a distant star.
Because Mercury orbits the sun very quickly, a day on Mercury lasts
longer than 58 days. If you were standing on Mercury at the equator and
timed how long it took the sun to go from directly overhead to sunset to
sunrise and then rise directly overhead again, it would take 176 Earth
days. These long days and nights allow for the temperatures to rise as
high, and fall as low, as they do.

## How long is a year on Mercury?

!Mercury from Mariner
10
Mercury has the shortest year in the Solar System. It is about 88 Earth
days long.

It used to be believed that the same side of Mercury always faced the
Sun. In order for this to be true, Mercury would have to take the same
amount of time to rotate (spin around) as it does to circle the sun.
From watching it carefully we now know that Mercury\'s rotation is
somewhat faster than its orbit. Because of the way the orbit and
rotation work together, on Mercury, a day (the time from one sunrise to
the next) is actually almost twice as long as a year.

## What is Mercury made of?

The center of Mercury is made of iron in partly-molten (liquid) form. We
know that there is iron at the center because the planet generates a
magnetic field. It contains more iron for its size than any other planet
in the Solar System. The rest of Mercury, its thick crust, is made of a
special type of rock called *silicate rocks*. There are craters near the
poles that are constantly in shadow. Some of these craters contain ice.
There is a huge crater on Mercury called Caloris Basin. It was formed
when a comet hit the planet and *lava* or molten rock filled the impact
crater. The round wall of this crater is over 2km tall.

## How much would Mercury\'s gravity pull on me?

If you were on Mercury, it would pull you down less than half (38%)as
much as the Earth. An item that weighs 100 pounds on Earth, would only
weigh 38 pounds on Mercury.

## Who discovered Mercury?

!A computer-generated simulation of MESSENGER orbiting
Mercury.
Nobody really knows who first discovered Mercury, but the first known
recorded observations of it are from tablets in Assyria about three and
a half thousand years ago, in the 14th century BCE. This was probably
something like an informational article about Mercury\'s movements. In
these tablets, Mercury is called (in translation) *The Jumping Planet*.
Almost every ancient civilisation had their own written records and
names for Mercury.

In 1639, an Italian astronomer named Giovanni Zupi observed that Mercury
has phases, like the phases of the Moon, as it orbits around the Sun.
This is evidence that it *does* orbit around the Sun, an idea that was
fairly new at the time, suggested less than a hundred century earlier by
Copernicus.

Before the twentieth century, it was a mystery to all the astronomers
how long it took for Mercury to rotate. They solved this mystery in
1962, when some astronomers sent radar signals to Mercury, which then
bounced back to Earth: it takes 59 days for Mercury to rotate.

It isn\'t easy to sent a space probe from Earth to Mercury, because
Mercury is much closer to the Sun and therefore orbits the Sun much
faster than Earth does. So a space probe would have to burn a lot of
fuel to match its speed with Mercury, in order to orbit---or land
on---the planet. In 1973, a space probe Mariner 10 was sent to take
measurements of Mercury and map its surface. Because orbiting Mercury
would be so expensive, Mariner 10 orbited the sun instead, and would
take pictures each time it got close enough to Mercury. Unfortunately,
when Mariner 10 finally ran out of fuel, it had only mapped about 45% of
the surface. However, it also discovered that Mercury has an iron-rich
core and a magnetic field. 29 years later, in 2004, another probe was
launched, named MESSENGER. MESSENGER stands for MErcury Surface, Space
ENvironment, GEochemistry, and Ranging. MESSENGER followed a complicated
path that would slowly match speeds with Mercury without using much
fuel. It passed by Mercury three times, and finally settled into orbit
around Mercury more than six years after it was launched. By March 2013,
MESSENGER had mapped 100% of the surface of Mercury.

## Who is this planet named after?

!A statue of Mercury. In Roman
mythology, Mercury (Latin *Mercurius*) was the messenger of the gods. He
wore a hat and sandals with wings on them, allowing him to travel around
the world very quickly. The planet Mercury was named after him because
it moves faster than any other planet in the Solar System. It moves
nearly 48 km *every second*! (Of course, the Romans didn\'t know that,
but they could see how fast it moved across the sky.)The Greeks called
this god Hermes.

Next Topic: Venus {{-}}

## References

NASA\'s Solar System
Exploration1\
Arnett, Bill. The Nine
Planets2\
Worldbook Online
3\
Worldbook@NASA,
\"Mercury\"4\
NASA Planetary Fact Sheet
5\
Hamilton, Calvin J. . Solarviews.com, \"Mercury\"
6\
Encyclopedia Mythica, \"Mercury\"
7\
Col, Jeananda. Enchanted Learning/Zoom Astronomy
8
1998-2005\
`<i>`{=html}Usborne Internet-Linked Science Encyclopedia`</i>`{=html},
Usborne Publishing Ltd.
9\
Dickinson, Terrence. `<i>`{=html}The Universe and Beyond`</i>`{=html} .
Firefly Books \
ar:ويكي الأطفال:نظام
شمسي/عطارد bs:Wiki junior
Sunčev sistem/Merkur
de:Wikijunior
Sonnensystem/\_Merkur
es:Wikichicos Sistema
Solar/Mercurio
nl:Wikijunior:Zonnestelsel/Mercurius
pl:Wikijunior:Układ
Słoneczny/Merkury
zh:Wikijunior:太阳系/水星


# Wikijunior:Solar System/Venus

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
!♀.svg "♀"){width="80"} **Venus Facts**:

-   Venera 7, the first space probe to land on Venus, was destroyed by
    the hostile conditions on Venus after only 23 minutes.
-   Almost all of the surface features on Venus are named after women.
-   A day on Venus is equal to 117 days on Earth.
-   It has been proposed that some microbes could live in Venus\'s
    clouds.

```{=html}
</div>
```
Venus is the second closest planet to the Sun. It is a *terrestrial
planet*. This means that we think it was created in a similar way to our
planet Earth and is made of rock. !Venus. You can\'t see the surface in
this picture; the white is the
clouds.

\
{{  }}

## How big is Venus?

!Earth and Venus
Comparison
Venus is only slightly smaller than the Earth. This is one reason why
Venus is sometimes thought of as Earth\'s \"twin\". Venus has a
*diameter* of about 12,100 km. It has also been visited by many probes.\

## What is the surface like on this planet?

!Maat Mons on the Surface of Venus, by radar
imaging
The surface of Venus is very different from the surface of the Earth. It
is very dry and hot enough to melt lead. The pressure on the surface is
very high. It is the same pressure as being 1 km (3,280 feet) below the
surface of the sea on Earth.

!Channels on the surface of Venus, looking like river channels on
Earth
Channels that look like rivers have formed on Venus. Scientists think
these channels are formed from erupting lava. The lava flows along as it
cools down, creating the channels. One feature only Venus seems to have
is unusual volcanoes called *arachnoids*. These are volcanoes that have
formed differently from other volcanoes we have found in the Solar
System. We don\'t know exactly how they were formed. Venus also has
volcanoes like those on Earth.

Parts of the surface of Venus look something like continents. The
largest of these areas is called *Ishtar Terra* (land of Ishtar, from
the Babylonian goddess who was similar to Venus). Deep basins like those
under the Earth\'s oceans have also been discovered. On Venus, though,
they have no water. Features like mountain ranges and meteor craters
have also been found on Venus. One of the highest mountains on Venus,
*Maxwell Montes*, is about 11 km taller than Mount Everest, the highest
mountain on Earth.

On the night side of the planet, there is a strange effect called *Ashen
Light*. For some reason, the dark side of Venus has a subtle glow. There
are various theories about this. One of the earliest theories --- now
disproved, of course --- was that there were aliens on Venus and they
were celebrating a new Venusian emperor. Currently, one of the more
believed ones is this: There is a high concentration of carbon dioxide.
When it is hit by the ultraviolet rays of the sun, they change into
carbon monoxide and oxygen, and emit green light. The entire chemical
procedure is .

!The Venera 13 Lander as depicted on a stamp, which made scientific
measurements and sent back pictures from the surface of
Venus

## How long is a day on Venus?

Venus *rotates* (spins around) even more slowly than Mercury. One full
rotation of Venus takes about 243 Earth days. Venus also rotates in the
opposite direction to most of the other planets in the Solar System. One
day on Venus, from noon to noon, depends on the length of the year as
well as the rotation time, and is about 117 earth days.

## How long is a year on Venus?

One year on Venus is almost 225 Earth days long. This is less time than
it takes Venus to rotate on its axis and less than two Venus days.

## What is Venus made of?

The surface of Venus, its crust, is covered in nothing but rock. But,
the core of Venus is made of nickel-iron. The atmosphere around Venus is
very thick and is made of carbon dioxide, nitrogen, and poisonous gasses
that create high pressure and trap in heat.

## How much would Venus\'s gravity pull on me?

If you were on Venus, it would pull you down almost as strongly as
Earth. The atmosphere exerts a pressure at the surface more than 90
times Earth\'s normal sea-level pressure.

## Who discovered Venus?

Because Venus is closer to the sun than we are on Earth, we always see
it close to the sun in the sky. So it only appears for us just before
sunrise in the eastern sky, or just after sunset in the western sky.
Many cultures thought Venus in the morning and Venus in the evening were
two separate things. The ancient Romans called the evening object Venus
(after the goddess of love) and the morning object *Lucifer* (which
means *light bearer* --- a servant who walked ahead of the sun\'s
chariot with a torch, to light the way). Nobody knows who first thought
the two were a single object. The first known *written* description of
them as one object was the Venus Tablet of Ammisaduqa, from about three
and a half thousand years ago --- 1581 BCE. !A map of where the Veneras
9-14 and Vegas
landed.

About three thousand years later, in 1610, Italian astronomer Galileo
Galilei used a telescope to observe that Venus has phases, just as the
moon does. Phases happen because only the side of Venus (or of the Moon)
facing the Sun is lighted. The phases of Venus supported the theory of
Copernicus that the planets go around the Sun. Then, a few years later
in 1639, an English astronomer named Jeremiah Horrocks observed a
*transit of Venus*. That\'s what it\'s called when Venus passes right
between the Earth and the Sun, so that Venus is visible from Earth
during the day as a tiny dot passing across the Sun. In 1761 a Russian
astronomer, Mikhail Lomonsov, watching another transit of Venus, saw
that Venus has an atmosphere.

Not much more was discovered about Venus until the 1920s. Then, a United
States astronomer, Frank Ross, observed Venus using ultraviolet light
--- the light that causes sunburn --- and for the first time saw the
structure of the clouds on Venus.

However, there is only so much that can be learned about Venus by
looking at it from Earth. The first successful pictures of Venus by a
space probe were taken by Mariner 2 in 1962. Mariner 2 was the first
space probe successfully sent to observe another planet. It showed two
important things: Venus has practically no magnetic field, and Venus has
temperatures of 490 to 590 K --- that\'s as hot as the inside of a
working oven on Earth!

!The first written record of Venus. It describes Venus\' movement over
21
years.

## Who is this planet named after?

Venus is named after the Roman goddess of love. Sometimes it can be seen
shining brightly just before dawn or just after sunset, when it is
called the Morning Star or Evening Star. Some people, like the Aztecs
and the Greeks, gave Venus two names -- one for the morning and one for
the evening.

Because Venus and the Earth are the same size, scientists call Venus
\"Earth\'s sister planet\". For a long time most scientists thought that
Venus had plants, animals, and possibly even people. However because
Venus is so hot we now know that it is impossible for anything to live
there.

## How long would it take people to get there?

It could take around a year and a half to get there. But it is very
unlikely someone would go to Venus.\

## References

-   Volcano World, \"Lava
    Flows\"1\
-   Astronomy Picture of the Day
    2\
-   Alder
    Planetarium3\
-   Mount Everest 4\
-   Windows to the
    Universe5\
-   NASA\'s Solar System
    Exploration6\
    Arnett, Bill. The Nine
    Planets7\
-   Worldbook Online
    8\
-   Worldbook@NASA,
    \"Mercury\"9\
-   NASA Planetary Fact Sheet
    10\
-   Hamilton, Calvin J. . Solarviews.com, \"Mercury\"
    11\
-   Encyclopedia Mythica, \"Mercury\"
    12\
-   Col, Jeananda. Enchanted Learning/Zoom Astronomy
    13
    1998-2005\
-   `<i>`{=html}Usborne Internet-Linked Science
    Encyclopedia`</i>`{=html}, Usborne Publishing Ltd.
    14\
-   Dickinson, Terrence. `<i>`{=html}The Universe and
    Beyond`</i>`{=html} . Firefly Books
    \

Next Topic: Earth

ar:ويكي الأطفال:نظام
شمسي/الزهرة bs:Wiki
junior Sunčev
sistem/Venera
de:Wikijunior
Sonnensystem/\_Venus
es:Wikichicos/Sistema_Solar/Venus
it:Wikijunior_Il_sistema_solare/Venere
nl:Wikijunior:Zonnestelsel/Venus
pl:Wikijunior:Układ_Słoneczny/Wenus
zh:Wikijunior:太阳系/金星


# Wikijunior:Solar System/Earth

Earth is the planet we live on. It is the only planet in the Solar
System with liquid water on its surface. It is also the only planet we
know to have *life* on it. Earth is also known as Terra.

```{=html}
<div style="float:right; border:2px solid #000000; width:250px; margin-left:0.2em; padding:0.4em; background-color:#f0f0ff">
```
!🜨.svg "🜨"){width="80"} **Earth Facts**

-   The Earth is the only planet we know to have life on it (such as
    ourselves.)
-   There is oxygen on Earth, and oxygen is necessary for life.
-   The Earth is the third planet from the Sun.
-   The Earth is the only planet we know that has liquid water on the
    surface, but scientists are trying to find others.
-   The Earth\'s axis is tilted which is why we have four different
    seasons.
-   The Earth is 4.6 billion years old.
-   The Hoba meteorite in Namibia is the biggest known meteorite to
    crash on Earth in one piece.

```{=html}
</div>
```
!A picture taken by Apollo 17, a space
mission.

\
== How big is the Earth? == The Earth is nearly 13,000 km wide. It\'s
the largest *terrestrial planet* in the Solar System.

The Earth\'s mass is about 5,973,700,000,000,000,000,000,000 kg. That\'s
a lot. But it is little compared with Jupiter (319 Earths) and tiny
compared with the Sun (335,789 Earths) or other stars!

## What is the Earth\'s surface like ?

The Earth\'s surface is made of rock. Most of it is underwater, but not
all. Islands of rock rise up out of the water. The biggest islands are
called *continents*, of which there are seven: North
America, South
America, Europe,
Asia, Africa,
Australia, and
Antarctica. The largest bodies of water are
called *oceans*, of which there are five:
Pacific,
Atlantic,
Indian, Arctic
and Antarctic or
Southern.

thumb\|right\|upright=2\|Anawhata beach, west of Auckland, New
Zealand The Earth\'s surface is made up
of huge *plates*. They are like huge jigsaw pieces made of rock. These
plates move very, very slowly, carrying the continents with them. They
can rub beside each other, push against each other, or even move away
from each other. If there are gaps between them, hot molten rock can
rise up and make *volcanoes*. Where the plates rub or push against each
other, *earthquakes* may happen. When two plates push each other\'s rock
upwards, *mountains* are formed.

!Zabriske Point, Death Valley National Park,
CaliforniaEarth
has many kinds of *environments*. It is cold and icy in places like
Antarctica. It is hot and dry in deserts like the Sahara in Africa and
Death Valley in the United States. It is cold and dry in deserts like
Siberia in Russia. Where it is warm and wet, rainforests grow.

## Why is there life on Earth?

Wherever we have looked on Earth, we have found living things. They may
be very small, like *bacteria*, but they are there. We have found
bacteria where it is very cold, very hot, very deep, very high or very
dark.

!Galileo being deployed after being launched by the Space Shuttle
*Atlantis*.jpg "Galileo being deployed after being launched by the Space Shuttle Atlantis")
What all living things on Earth seem to need is *liquid water*. Wherever
you can find some water, there are almost always living things there
too, even if you can\'t see them. If we find liquid water somewhere else
in the Solar System, scientists think we might find some living things
there too. If we don\'t, there is always the rest of the universe to
explore!

There is another possibility. All the living things we know need liquid
water. But maybe somewhere else there are living things that don\'t need
water. Perhaps we will need to learn how to recognize them.

\
== What about the Earth\'s moon? == Earth has one moon we call\... the
Moon!  Sometimes it is called
by its name in Latin, *Luna*, so we don\'t get confused with other
planets and their *moons*. The Moon has also been called Selene
(pronounced \"suh-LEE-nee\") which is Greek for moon and was the name of
the Greek moon goddess.

Recently we have also found some other objects that are said to go
around the Earth. The largest one, called
Cruithne (pronounced \"cru-EE-nyuh\"), is
three miles wide. In fact, it *orbits* (goes around) the Sun in a way
that makes it keep coming close to Earth.

There are various ideas about where the Moon came from (no-one was
around to see it happen, after all), but the most widely held theory is
that when Earth was young, a large body hit Earth and split off a
section of the Earth that is now the Moon.

## How long is a day on this planet?

A day on Earth is 24 hours long. That\'s daytime *and* night time. A 24
hour day is how long it takes the Earth to spin around once. On the half
of the Earth that is facing the sun it is daytime and on the half of the
Earth that is facing away from the sun it is nighttime.

The spin of the earth is also the reason why the sun appears to rise in
the east and to set in the west. Although it looks like the sun is
moving from the surface of the earth, it is really the surface of the
earth that is moving. The reason we do not feel like we are spinning is
because the earth is so big compared to the size of people.

Also, the Earth is tilted at about 23°, so there are times that the
North or South pole is always facing or turned away from the sun. If you
live at one of the poles of Earth it can be light or dark throughout the
whole day!\
{{  }}

## How long is a year on this planet?

A year on Earth is about 365 and 1/4 days long. That\'s how long it
takes the Earth to orbit the Sun once. Approximately every four years we
have a leap year. A leap year contains an extra day in our calendar on
February 29th in order to account for the 1/4 of a day left over each
year.

## What is the Earth made of?

![](Inside_the_Earth.PNG "Inside_the_Earth.PNG")\
When a planet is made of rock, we call its surface the *crust*. Below
the Earth\'s crust is hot rock, some of which is molten. It is in a
layer called the *mantle*. The hot molten rock is what comes out of
volcanoes. It\'s then called *lava*.

Under the mantle is the *core* of the Earth. We think it is made from
solid iron and nickel, surrounded by hot molten iron. The temperature
there is very very hot!

The Earth\'s crust is very thin compared to the mantle and the core. But
it is very thick to us. Nobody has drilled all the way through it yet.
Even the deepest underground mines are far away from reaching its
deepest base.

## How much does the Earth\'s gravity pull on me?

It\'s easy to find your weight on Earth by using a scale. You have
weight because the Earth\'s **gravity** pulls you towards its center.
Normally, the ground or the floor get in the way, making you feel
\'stuck\' to them.

There are several kinds of scales:

!A pan balance{width="160"} 1) Comparing
of 2 masses (weights). You put the thing(s) you want to weigh on one pan
(like some marbles), and then you put several \"weights\" on the other
pan until the pointer shows that both pans have equal weights on them.
Then you look at the pan with the known weights on it, and add them all
up. The total is the mass of the thing(s) you want to weigh. !A spring
balance{width="60"} 2) A spring
balance usually has a hook on it, with a pan. You put the thing(s) you
want to weigh on the pan, the spring is pulled, and the greater the
weight, the further the spring is pulled. That distance, calibrated in
pounds or kilogram (or whatever), is usually shown either on a dial or
on a linear scale. !electronic
balance{width="100"} 3)
There are also electronic scales that give a properly calibrated
reading---grocery stores, for example, use these.

NOTE: **Gravity** varies slightly depending on the location where you
want to get the weight; spring balances and some electronic scales can,
in theory, read slightly different weights at different places because
of that, but usually in practice that difference is too small to be
noticed. But, because the balance type of scales work differently from
the spring or electronic types, they will always read the true, correct
mass. They would even give the same mass on the Moon, where gravity is
much less than on Earth.

![](Isaac_Newton_cartoon.png "Isaac_Newton_cartoon.png")

**Did you know?** that *Sir Isaac Newton* was the first person to
realize that the force pulling you down to the ground was the same force
that keeps the planets going around the Sun? The story goes that he
thought of this when he saw an apple fall from a tree.

Gravity is a very important force. As well as keeping you firmly stuck
to the Earth, it keeps the Moon going round the Earth, The Earth going
around the Sun and the Sun going around the center of the Milky Way
**galaxy**. Gravity also makes stars and planets a nice round ball
shape. In fact without gravity there wouldn\'t even *be* a Sun, Moon or
Earth because the material that they are made of would just float away
into space.

\
== Who is it named after? == !The Earth seen from the
Moon

The word earth is used for both planet Earth and soil. Other names had
been used for Earth such as Gaia, Tellus and Terra. Gaia is the Greek
goddess (meaning Mother Earth) and Terra is the Roman name of the same
goddess. Tellus is the Latin for \"Earth\", many scientific words
dealing with Earth will be derived form Latin.

Next Topic: Moon

## References

\"It is also the only planet we know\...\"
1
2\
\"The Earth is nearly\...\"
3
4\
\"The Earth\'s mass\...\"
5\
\"Earth\'s surface is made of\...\"
6
7

ar:ويكي الأطفال:نظام
شمسي/أرض bs:Wiki junior
Sunčev sistem/Zemlja
de:Wikijunior Sonnensystem/
Erde es:Wikichicos
Sistema Solar/La
Tierra
fr:Wikijunior:Système_solaire/La_Terre
nl:Wikijunior:Zonnestelsel/Aarde
pl:Wikijunior:Układ_Słoneczny/Ziemia
zh:Wikijunior:太阳系/地球


# Wikijunior:Solar System/Moon

{{/Coolfacts\|=
1\|!☽.svg "☽"){width="80"}\|=
2\|Moon Facts\|= 3\|

-   When we look at the Moon from Earth, we always see roughly the same
    side. Until Luna 3 sent back photos in 1959,
    no-one knew what the other side looked like.
-   The Moon is nearly twice as big as
    ../Pluto/.
-   The \"Man in the Moon\" isn\'t always seen as a man. People from
    India see an old woman with a spinning wheel. People from Mexico see
    a rabbit!
-   The Moon isn\'t that small compared to the Earth - it\'s actually
    the largest moon in the solar system, relative to the size of its
    planet. Sometimes the Earth and Moon together are called a *binary*
    or *double planet system*.
-   The Moon is the fifth largest moon in the solar system.
-   In 2002, another object appearing to be an asteroid was observed
    orbiting around the Earth. Later it was found to be a rocket
    booster.

}} ! The Moon is our nearest neighbour in
space.

## How big is the moon?

!Comparison of the size of the Moon and the
Earth
Most of the planets in the Solar System are much bigger than their
moons, but the Earth and the Moon are much closer in size. The Moon is
just under 3,500 kilometers (km) wide. That\'s over a quarter of the
size of the Earth (about 12,600 km wide) as you can see in the picture
below. Because of this, the Earth and Moon together are sometimes called
a *binary* or *double planet system*.  {{
 }}

## What is the moon\'s surface like?

!Astronaut Harrison Schmitt collecting rocks from the Moon during the
Apollo XVII
mission.
!A map of the
moon. The Moon has
no atmosphere. It also has no liquid water on its surface. During the
day it becomes very hot, but at night it is icy cold. A person visiting
the Moon needs an air supply and a special suit.

The Moon has many *craters* on its surface. The largest one is called
the *South Pole-Aitken Basin* and is roughly 2500 km across.

We think nearly all the craters on moons or planets were made by huge
rocks hitting them a long time ago. These collisions are called
*impacts.*

Some of the craters on the Moon look as if they have rays coming out of
them. These rays are rocks thrown across the Moon by the impacts that
made the craters. Some of the craters around the poles of the Moon may
have ice in them.

There are also darker areas called *maria* (said \"MARR-ee-ah\"). These
are large pools of lava that cooled a long time ago. Most maria are on
the side of the Moon we see from Earth. The lighter areas on the Moon
are highlands.

## How long is the Moon\'s revolution?

The Moon takes just over 27 Earth days to *rotate* (rotate means spin
around) once.

## How long is a year on the moon?

The Moon also takes just over 27 days to *orbit* (move around) the
Earth. This is why we always see the same side of the Moon when we look
from the Earth. We call this side the *near* side. The other side we
call the *far* side. In 1959, a probe called *Luna 3* sent back pictures
of the far side. That was the first time anyone saw what it looked like.

## What is the Moon made of?

The surface of the Moon is made of rocks and dust. The outer layer of
the Moon is called the *crust*. The crust is about 70 km thick on the
near side and 100 km thick on the far side. It is thinner under the
maria and thicker under the highlands. There may be more maria on the
near side because the crust is thinner. It was easier for lava to rise
up to the surface.

We think the Moon has a small *core* (center) about 300 km across. The
core is composed of solid iron. Because the core is solid, the Moon does
not have its own magnetic field.

## How much would the Moon\'s gravity pull on me?

If you were on the Moon, it would pull you down about a sixth as much as
the Earth does, so you\'d weigh a sixth as much. So would anything else.
That\'s why it was much easier for the astronauts visiting the Moon to
pick up rocks there.

## Who is the moon named after?

!The goddess Diane, the goddess of the Moon in Roman
mythology
The names *Moon* and *month* both come from the ancient Greek name for
the Moon, *Mene*. There have been other names for the Moon, like
*Selene* and *Luna*. Selene was the Greek goddess of the Moon. Luna was
the Roman goddess of the Moon. The Roman people also associated their
goddess Diana with the Moon.

## Who discovered the Moon?

Ancient Greece and Ancient China noted over 2000 years ago that the
light from the Moon is reflected from the Sun. Also, Ancient Greece
noted that the Moon causes tides on Earth. More recently, Luna 1 was the
first spacecraft to perform a flyby of the moon. Luna 2 was the first
spacecraft to land on the moon, and Luna 3 was the first to photograph
the far side of the Moon which you can not see from Earth. Luna 1
through 3 all were launched in 1959. Surveyor 3, in 1967, was the first
to examine the soil of the Moon. It dug to 17.5 cm. In 1969, Apollo 11
was the very first spacecraft to land people on the moon.

Next Topic: Mars

## References

\"The Moon is just under\...\" 1
2\
\"So the Earth and the Moon together\...\"
3
4\
\"The Moon does not have any atmosphere.\"
5
6\
\"During the day it becomes\...\"
7
8\
\"The largest one is called\...\"
9
10\
\"These rays are rocks\...\"
11\
\"Some of the craters around the bottom\...\"
12
13\
\"There are also darker areas\...\"
14
15\
\"The lighter areas\...\"
16\
\"The Moon takes just over 27\...\"
17
18\
\"We call this side\...\"
19
20
21\
\"The other side we call\...\"
22
23\
\"The surface of the Moon\...\"
24
25
26
27\
\"\...it would pull you down\...\"
28
29\
\"The names \"Moon\" and\...\"
30
31
32\

ar:ويكي الأطفال:نظام
شمسي/القمر bs:Wiki junior
Sunčev sistem/Mjesec
de:Wikijunior Sonnensystem/
Mond
zh:Wikijunior:太阳系/月球


# Wikijunior:Solar System/Mars

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
!♂.svg "♂"){width="80"} **Mars Facts**:

-   Mars is red because of rust in the surface rocks
-   A volcano on Mars called *Olympus Mons* is the highest mountain in
    our Solar System.
-   Mars has polar ice caps that look like the ones on
    ../Earth/.
-   Mars has ancient river beds where scientists think liquid water
    flowed millions or billions of years ago.
-   The *Tooting* crater on Mars was named after a suburb in London
    because the discoverer \"thought \[his\] mum and brother would get a
    kick out of having their home town paired with a land form on
    Mars\".

```{=html}
</div>
```
Mars is the fourth planet from the Sun. It is called a *terrestrial*
planet because its outer layers are made of rocky material like the
Earth.

## How big is the planet?

!Comparison of the size of Mars and the
Earth
Mars is the second smallest of the eight major planets in the Solar
System. Only Mercury is smaller. It is nearly 7,000 kilometres (km)
wide; just over half the width of the Earth. Its volume is about 15% of
the Earth. Since a lot of the Earth is covered by water, the total
surface area of the Mars is nearly as large as all of the land on the
Earth. It is possible that its size may eventually permit human
colonies.

## What is its surface like?

center\|thumb\|upright=3\|A panorama view from the Mars rover
*Spirit*.

The surface of Mars is a lot like a desert on Earth; it is very dry and
dusty, but it is also very cold. There are a lot of loose rocks and
dunes of fine sand. Crater impacts mark the surface, but these are not
as common as on the Moon. One of the craters is the huge *Hellas
Planitia*. It is about half the size of the continental United States.
The southern half of the planet has more craters than in the north. The
south is also higher in elevation.

!An overhead view of *Olympus Mons*, the highest mountain in the Solar
System.
There is an area on Mars called the *Tharsis Bulge*, which has four huge
volcanoes. These volcanoes have not erupted for millions of years. The
largest volcano is called Olympus Mons. It is 27 km tall, making it the
highest mountain in the Solar System; *more than three times* higher
than Mount Everest on Earth. It is 625 km across and takes up an area as
big as the US state of Arizona. Mars also has a huge canyon called the
*Valles Marineris*. It is much bigger than the Grand Canyon on Earth. It
is 4000 km long, up to 7 km deep and up to 200 km wide. Scientists think
that when the *Tharsis Bulge* was created, the surface of Mars cracked
to form the *Valles Marineris*.

Like the Earth, Mars has ice caps at its poles. However, they are made
from frozen carbon dioxide as well as ice. During the Martian winter at
each pole, the cap grows as carbon dioxide from the atmosphere freezes.
The cap shrinks again during the Martian summer. As on Earth, when it is
winter at one pole it is summer at the other.

In some places, there are dry *channels* that look like they were made
by running water. So, a long time ago Mars may have had lakes and
streams made of water. Now all of the water is frozen into ice under the
surface.

There is an atmosphere on Mars, but it is very thin. There is also much
more carbon dioxide in it than oxygen. (Oxygen is the gas we need when
we breathe in; carbon dioxide the gas we get rid of when we breathe
out.) So, we would need spacesuits to visit Mars. The atmosphere helps
protect the surface from smaller meteorites.

When Mars comes closest to the Sun, the atmosphere can stir up storms of
dust. Some of these storms are gigantic; they can cover the entire
planet in clouds of dust. Dust storms on Mars can last for hundreds of
days, with wind speeds of up to 200 kilometres per hour. Huge storms
like these have been seen from the Earth through telescopes.

{{  }}
{{/Mars}}

## How long is a day and year on this planet?

One day on Mars is only 39 minutes and 35 seconds longer than a day on
Earth (1.026 Earth days). A year on Mars is almost two Earth years long
(687 Earth days).

Much like the Earth, the axis of rotation of Mars is tilted at an angle.
This tilt causes seasons on Mars as it travels around the Sun. Summer
occurs on the half of the planet that is tilted toward the Sun, and
winter on the other half. After half a Martian year has passed, the
seasons are reversed. But these seasons are about twice as long as on
Earth.

## What is it made of?

!visualization of the Martian
interior.

The outer, rocky surface of Mars is called the crust. Most of the crust
is made from basalt, a type of rock made when lava grows cold.

Like the Earth, Mars has a thick layer of rock below the crust called
the mantle. The mantle is much hotter than the crust, and the mantle
rock is partly molten. But the crust on Mars has grown thick, so the
lava from the mantle no longer reaches the surface. There are volcanoes
on Mars, but they are no longer active.

At the center of Mars is a core made of the metals iron and nickel. If
Mars were the same size as the Earth, the core of Mars would be smaller
than the Earth\'s core. So a larger amount of Mars is made out of rock.
Because rock is lighter than the metals in the core, Mars has a lower
density than the Earth.

## How heavy would I be on Mars?

!Detailed picture of Mars

If you were on Mars, you would be lighter, as Mars\' gravity only has a
force about two fifths as strong as the that of Earth\'s. You could lift
objects that weigh almost three times as much compared to similar
objects here on the Earth. You could jump up almost three times higher,
and it would take much longer to fall to the ground from the same
height.

Even though it looks as though you would be like a comic-book hero on
Mars, there are some things you couldn\'t do. Although a big rock would
*weigh* less and you could pick it up, it would still have the same
*mass*. If you tried to catch it, it would knock you over, and if it
landed on you it would crush you. A car on the surface of Mars would
need the same amount of power to speed up, although going uphill would
be less of a problem. It may, however, need more room to stop. Because
of the reduced gravity a vehicle would not \"grip\" the ground on Mars
as strongly, but the constant mass would keep the vehicle moving just as
strongly, making it easy to go into a skid.

## Who was it named after?

In Roman mythology, Mars was the god of war and agriculture. The planet
Mars was named this because the planet looks red like blood, from rust
in its surface rocks.

## Who discovered Mars?

Nobody knows, but the earliest records we know of were by Ancient
Egyptians, more than 4000 years ago, noting Mars\' movement. On one
pharaoh\'s tomb, named *Seti I*, Mars is drawn on the ceiling. The
Babylonians (in the Middle East), Chinese, and Greeks also studied Mars
more than 3000 years ago. The Greeks learned about Mars from the
Babylonians, and since the Babylonians called it their god of war, named
*Nergal*, the Greeks called it their own god of war, *Ares*. Exploration
of Mars was first attempted in 1960, with Mars 1. It failed, along with
several other missions by the Soviet Union in the 1960s. The first
successful mission to Mars was in 1964, by Mariner 4, by the U.S. Most
of the other Mariner missions to Mars were successful. The last Mariner
mission to Mars, Mariner 9, got there in the midst of a dust storm, and
orbited the planet for several months before it could get a good look at
the surface. So far, all these missions were flybys or orbiters. The
first spacecraft to land on Mars was Viking 1 in 1976. Viking 2 landed
19 days later. Together, they took many good pictures of Mars\' surface.

{{multiple image

align = left

width1 = 100

width2 = 110

width3 = 122

width4 = 123

width5 = 100

width6 = 196

image1 = Mars Viking 11h016.png

caption1 = Viking 1 lander site (February 11, 1978).

image2 = PIA00563-Viking1-FirstColorImage-19760721.jpg

caption2 = Viking 1 lander site (1st color, July 21,
1976).

image3 = First Color Image of the Viking Lander 2
Site.jpg

caption3 = Viking 2 lander site (1st color, September 5,
1976).

image4 = Vl2 22g144-MarsViking2-19770925.gif

caption4 = Viking 2 lander site (September 25, 1977).

image5 = Mars Viking 21i093.png

caption5 = Frost at Viking 2 site (May 18, 1979).

image6 = Mars Viking 12a240.png

caption6 = Martian sunset over Chryse Planitia at Viking 1 site
(August 20, 1976).

}}

Next Topic: Asteroid belt

## References

-   Steven W. Squyres, *Mars*, World Book Online Reference Center, World
    Book, Inc., 2004.
    1
    2
-   \"a *terrestrial* planet\"
    3
-   \"How big is the planet?\"
    4
    5
-   \"How long is a day on this planet?\"
    6
    7
-   \"What is it made of?\" Steven W. Squyres, *ibid.*

ar:ويكي الأطفال:نظام
شمسي/المريخ bs:Wiki
junior Sunčev sistem/Mars
de:Wikijunior Sonnensystem/
Mars
es:Wikichicos/Sistema_Solar/Marte
nl:Wikijunior:Zonnestelsel/Mars
pl:Wikijunior:Układ_Słoneczny/Mars
fi:Wikijunior_Aurinkokunta/Mars
zh:Wikijunior:太阳系/火星


# Wikijunior:Solar System/Asteroid belt

!Asteroid belt between Mars &
Jupiter.PNG

The asteroid belt lies between the planets Mars and Jupiter. It contains
lumps of rock and metal much smaller than planets. These lumps are
called asteroids or minor planets. They are not visible from Earth with
the naked eye, but many may be seen through binoculars or small
telescopes.

+------------+----------+
| Object\    | Maximum\ |
| Name       | Size     |
+============+==========+
| 1 Ceres    | 933 km   |
+------------+----------+
| 4 Vesta    | 530 km   |
+------------+----------+
| 2 Pallas   | 525 km   |
+------------+----------+
| 10 Hygiea  | 407 km   |
+------------+----------+
| 511 Davida | 326 km   |
+------------+----------+

: Largest bodies in the asteroid belt

The largest asteroid in the solar system is called \"2001 KX76.\" In the
asteroid belt, the four largest bodies are Ceres (a dwarf planet named
after the Roman goddess of agriculture), Vesta (the Roman goddess of the
home), Pallas (the granddaughter of Poseidon), and Hygiea (the Greek
goddess of health). These four bodies make up about half of the asteroid
belt.

Some asteroids are less than a kilometer across. Unofficially the limit
has been set at 50 meters, and anything smaller than that is going to be
simply called a meteoroid. With advances in telescopes and particularly
for objects that travel close to the Earth, some objects smaller than 50
metres have indeed been seen passing nearby the Earth.

There are probably several million asteroids in the solar system. Over
96,000 asteroids have been given numbers. Almost 12,000 of them have
names. But even though there are a lot of asteroids, the asteroid belt
is mostly empty space. Traveling through the asteroid belt in a space
ship would not be very much like what you see in a science fiction film.
This would not be the same in the first 100 million years of the solar
system\'s history (had humans evolved and discovered film). The asteroid
belt lost 99.99% of its mass in the first 100 million years of the solar
system.

{{  }}

## What are they named after?

The first asteroids were named after mythical heroes and gods much like
the major planets. The first to be discovered was named Ceres after the
Roman goddess of growing plants (particularly grain) and of motherly
love. The second asteroid discovered was called Pallas and was named
after one of the Greek gods of wisdom. Asteroids are also given a number
in the order of their discovery, so Ceres is 1, Pallas is 2, and so
forth.

As the number of known asteroids increased, they ran out of mythical
names so other names were used instead. Some asteroids were named after
countries. For example asteroid number 136 is named Austria. Others were
named after plants, for example 978 Petunia. 1620 Geographos was named
after the National Geographic Society, in recognition to their efforts
at sharing knowledge about the Solar System. Many are named after
people, both alive and dead. In a couple of cases, like 2309 Mr. Spock,
asteroids were named after the discoverer\'s pet cat. This last type of
naming is discouraged, but it still happens from time to time. Even
fictional characters have been used.

Today, names for asteroids can be suggested by the people who discover
them. The names become official after a group of people reviews them to
make sure they are not offensive or too much like another name. Because
so many asteroids are now being found, most new asteroid discoveries are
not even getting a name at all, but rather a numbered code. It is not
likely that they will ever be given a formal name, at least in this
century.

The actual word *Asteroid* can refer to any member of the family of
Asteroidea; in other words, a starfish. The etymology of the word comes
from Ancient Greek *ἀστεροειδής*, literally meaning star form. The
Ancient Greeks probably must have mistook the asteroids for stars.

Most of the asteroids have symbols representing them; for example, Ceres
has ⚳, representing Ceres\'s scythe, and Pallas has ⚴, reperesenting
Athena\'s spear.

## Who discovered them?

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
**Asteroid Belt Facts**:

-   The total mass of all the asteroids in the asteroid belt is about
    1/35th of that of our moon.
-   The largest object in the asteroid belt, Ceres, makes about 1/3 of
    the total weight of all the asteroids.
-   Ceres is the only dwarf planet in the asteroid belt.
-   Vesta is the only asteroid that can ever be seen with the naked eye.
    Its magnitude can reach +5.1, about the same as Uranus.
    -   Although people probably saw Vesta and Uranus thousands of years
        ago, they were not recognised to orbit the Sun until 200 years
        ago.

```{=html}
</div>
```
The first asteroid to be discovered was Ceres, on 1 January 1801, by
Giuseppe Piazzi accidentally. At first he thought this was a comet, then
later a planet! When it was realised it was too small Sir William
Herschel (the astronomer who discovered Uranus) made up the word
\"asteroid\" to describe it, using the Ancient Greek word *aster*,
meaning star, and the *-oid*, meaning form or shape. In other words a
star-like planet, because he couldn\'t see any details due to the small
size of the object.

By 1807 another 3 asteroids were discovered, but no more were found
until 1845 when a persistent asteroid hunter named Karl Ludwig Hencke
found a fifth, and sixth asteroid in 1847. Ever since then at least one
new asteroid has been found each year.

In 1891, the first pictures of the night sky were taken to find more
asteroids. This led to the discovery of many more asteroids. A picture
of the same part of the sky is taken on two different nights. When the
two pictures are lined up, the stars will be in the same places but an
asteroid will have moved.

In our modern times, over 280,000 asteroids have been discovered. Many
more are being found all the time. Some of these asteroids pass near the
earth and astronomers want to find any that come close to our planet.
Large numbers of asteroids are now being discovered by machines.

## What are they made of?

Three out of four asteroids are made of rock that is rich in carbon. The
rest are made of the metals iron and nickel. About half of these are
pure iron and nickel; the rest are mixed with compounds of silica, the
element that makes up rocks. Each of the larger metal asteroids contains
huge amounts of iron: much more than is mined every year on Earth.
Vesta, the brightest asteroid, has a very unusual composition - being
made of high-density volcanic rocks.

Scientists are very interested in what asteroids are made of because it
can help them learn how the solar system was formed. Several spacecraft
have visited asteroids to learn more about them.

## Are there asteroids outside of the asteroid belt?

framed\|right\|All the major asteroid clusters in the solar system. It
does look like the asteroid belt is clustered in the picture, but one
millimetre of emptiness in the picture means millions of kilometres
emptiness.Most asteroids are
found in the asteroid belt, but not all. Some asteroids orbit closer to
the Sun, and many asteroids orbit beyond Neptune. Asteroids that closely
approach Earth are called Near-Earth Asteroids. Sometimes pieces of
asteroids strike the Earth, burning in the atmosphere as a meteor. If
they are large enough, they might actually hit the surface and become
meteorites.

!Asteroid Ida and its
moon

A centaur is a mythical beast having a horse\'s body with a man\'s head
and torso in place of the head and neck of the horse. There are some
asteroids in the outer solar system that are called Centaurs. It is hard
to tell whether any one Centaur is an asteroid, comet, or Kuiper Belt
object. For example, the first Centaur to be discovered was Chiron(In
Greek Mythology, an important centaur). But some scientists think it is
a comet, not an asteroid. Officially it is called both the asteroid 2060
Chiron and the comet 95P/Chiron!

In most cases when an asteroid\'s orbit crosses the path of a planet
such as Jupiter, at some point the asteroid will either hit the planet
or else be hurled into another orbit. Many of the small moons of some
planets may have once been asteroids that were captured by the planet\'s
gravity when they came too close. However there are two points along the
orbit of a planet were an asteroid can safely linger. These are found at
a point one-sixth (or 60°) of an orbit ahead of the planet, and the same
distance behind the planet. These sites are called Lagrange points, and
they are found where the force of gravity from the Sun and the planet
balance out with the motion of the asteroid\'s orbit. The asteroids
found in these spots are called Trojans, and they move around the Sun at
the same velocity as the planet.

## Ceres

!The dwarf planet
Ceres._(cropped).jpg "The dwarf planet Ceres."){width="150"}

Ceres is a large Dwarf Planet like Pluto located in the asteroid field.
The difference between Ceres and most other dwarf planets is that it is
also an asteroid. Ceres is one of the few asteroids that are shaped like
a sphere, and it may have some ice just underneath its dusty surface. It
was discovered in 1801 by Giuseppe Piazzi, who was an Italian
astronomer.

## Some famous asteroids

Ceres the first discovered and biggest asteroid in the solar system.

The asteroid Ida has its own moon named Dactyl. A number of asteroid
moons have now been found.

Next Topic: Jupiter

## References

-   U.S. Naval Observatory Ephemerides of the Largest
    Asteroids,
    USNO.
-   Near Earth Asteroid Tracking, NASA.
-   Asteroids: Structure and composition of
    asteroids, ESA.
-   Main Asteroid Belt,
    SolStation.

pojas
de:Wikijunior Sonnensystem/
Asteroidengürtel
es:Wikichicos/Sistema_Solar/Cinturón_de_asteroides
nl:Wikijunior:Zonnestelsel/Planetoïdengordel
pl:Wikijunior:Układ_Słoneczny/Pas_planetoid
fi:Wikijunior_Aurinkokunta/Asteroidivyöhyke
zh:Wikijunior:太阳系/小行星带


# Wikijunior:Solar System/Jupiter

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
!♃.svg "♃"){width="80"} **Jupiter Facts**:

-   Due to its magnetic field trapping particles from the Sun, Jupiter
    is surrounded by very powerful radiation belts which would kill
    anyone who entered them.
-   Jupiter\'s moon Europa is thought to have a giant ocean below its
    surface.
-   Jupiter\'s moon Ganymede is the largest moon in the solar system.
-   Jupiter is the third brightest object in the night sky, second being
    Venus and first being the Earth\'s moon.
-   Jupiter has more than twice the mass of all the other planets in the
    solar system combined.
-   Jupiter is considered an almost-star. The smallest red dwarf star
    was only 30% bigger than Jupiter.
-   Jupiter\'s red spot and the Earth are close to the same size. That
    means that there is a storm going on in Jupiter that is as big as
    the Earth!
-   *Jovian* in English means anything relating to Jupiter --- the god
    or the planet. Sometimes the four outer planets are called the
    Jovian planets.

```{=html}
</div>
```
**Jupiter** is by far the largest planet in our Solar System: two and a
half times larger than all of the other planets put together. It is the
fifth planet from the Sun and one of the brightest planets as seen from
Earth. Jupiter, along with Saturn, Uranus and Neptune, is sometimes
called a \"gas giant\" because most of these planets are made up of
liquid and gas.

## How big is the planet?

!Comparing the sizes of the Sun, Jupiter, Earth, and the Moon. Notice
the red spot is about the size of the Earth!

Jupiter is 142,984 km or about 11 Earths in diameter at the **equator**.
That makes it about one tenth as big in diameter as the Sun! You could
fit about 1,400 Earths into the volume of Jupiter. It is 133,709 km or
10 Earths in diameter from pole to pole. Jupiter\'s rapid **rotation**
(it spins around in under ten hours compared with 24 hours for Earth)
makes it bulge out at the equator.

Jupiter\'s magnetic field is the largest single planetary thing in the
Solar System. It is 26 million kilometers across, making it about 20
times bigger than the Sun. It has a tail that extends past Saturn\'s
orbit. If it could be seen from Earth, it would appear to be five times
the size of the full moon.

## What is the surface like on Jupiter ?

!Jupiter\'s
atmosphere The
surface we see is not solid. This enormous planet has a relatively small
solid and rocky core. Liquids and gases surround this core and blend
with the atmosphere.

Jupiter is a cloudy, windy and stormy planet. It is always covered by a
layer of clouds, and wind speeds of 600 km/h are not uncommon. The
storms are visible as swirls, bands and spots. A particularly violent
storm, about three times Earth\'s diameter, is known as the Great Red
Spot. This storm has been in existence since at least 1831, and maybe
since 1665. If the storm has existed since 1665, that would make it more
than 300 years old!

The layer of clouds is divided into several bands. The lighter colored
bands are called **zones** and the darker bands are called **belts**.
The colors are caused by small changes in the temperature and chemistry.
Each band rotates in the opposite direction from its neighbors. Along
the edges where the bands meet, these winds collide and create swirling
patterns.

The stormy atmosphere of Jupiter has flashes of lightning just like on
Earth. However, while Earth\'s lightning strikes may be hotter than
50,000 °C, Jupiter\'s lightning strikes may go over 5,000,000 °C, which
is a hundred times more than Earth lightning, and is more than the
temperature of the sun\'s corona. The lightning is made by water near
the tops of the clouds.

## What are its rings like?

!The rings of Jupiter as seen by the Voyager 2
spacecraft
Jupiter\'s rings are dark and hard to see. They are made of tiny
particles that meteors knocked off Jupiter\'s small inner moons and
debris left over from comets and other objects that came close to the
surface of Jupiter. In fact, until the Voyager spacecraft arrived near
Jupiter and took closeup pictures of the rings of Jupiter, scientists
didn\'t even know that it even had rings at all. Two rings are clearly
from material that can be associated with two sets of the inner moons of
the planet.

These are the names of the rings and their sizes:

  Ring Name          Inner Radius   Outer Radius
  ------------------ -------------- --------------
  Halo               100,000 km     122,000 km
  Main               122,000 km     129,000 km
  Gossamer (inner)   129,000 km     182,000 km
  Gossamer (outer)   182,000 km     225,000 km

  : **Rings of Jupiter**

Gossamer means in English anything that is delicate, light, and flimsy.

{{  }}

## What is the planet\'s atmosphere made of?

!Jupiter as seen by the space probe *Cassini*. This is the most
detailed color portrait of Jupiter ever
assembled.
In the outermost layer of Jupiter lie frozen Ammonia crystals. (Ammonia
is a compound of hydrogen and nitrogen; its scientific designation is
NH~3~.) crystals.

Jupiter\'s atmosphere is mainly made of **hydrogen**(H~2~). Near the
surface, there is almost 90% hydrogen. Apart from this, the atmosphere
has helium(He). Because of the high pressure, helium becomes a liquid
further down in the planet. In addition, Jupiter has
methane(CH~4~)(0.3%), hydrogen deuteride(HD)(0.003%),
ethane(C~2~H~6~)(0.0006%), and least of all, water(H~2~O)(0.0004%).

Jupiter\'s temperature is very high. Because of this, scientists cannot
tell all the materials the planet is made of. The outer core of Jupiter
has hydrogen. The pressure present can make the gas solid. However,
because of the very high temperature, the gas melts, and becomes liquid.

## What are its moons like?

!A simulation of the orbit paths of the moons of
Jupiter.
Jupiter has 95 known moons. There are four major moons that were
discovered by Galileo in 1610, the first moons ever discovered around
another planet. Those moons are Io, Europa, Ganymede and Callisto; they
are named from characters in mythology closely associated with Jupiter.
They are called the Galilean moons. There are often **eclipses** on
Jupiter\'s cloud tops by the Galilean moons.

### Amalthea Group

There are four small moons **orbiting** inside Io\'s orbit. That group
is called the Amalthea group because Amalthea is the largest one. They
are all small and potato shaped. Amalthea is very red. The material of
Jupiter\'s rings came from meteors knocking it off of those moons.
Amalthea(Greek:Ἀμάλθεια) in Greek mythology is a foster mother of Zeus.

### Io

!The four largest moons of Jupiter. From left to right with increasing
distance: Io, Europa, Ganymede,
Callisto..tif "The four largest moons of Jupiter. From left to right with increasing distance: Io, Europa, Ganymede, Callisto.")
Io (pronounced EYE-oh) is Jupiter\'s closest major moon. It is 3643.2 km
across, slightly larger than Earth\'s Moon. It has the most spectacular
**volcanoes** in the solar system and molten **sulfur** lakes. Any
craters formed by asteroids hitting the surface are quickly covered up
by the volcanic activity. Io\'s core is made of molten **iron** and is
surrounded by a rock shell. Unlike Jupiter\'s other moons, there is very
little water on Io. Scientists think that when Jupiter was forming, it
was hot enough to dry out Io, but not the other major moons. In Roman
mythology, Io(Ancient Greek:Ἰώ) was a beautiful young nymph(Nymphs are
divine spirits that animate nature and generally portrayed as beautiful
young women.) that Zeus loved.

### Europa

Europa (pronounced *Eurṓpē*) is 3,121.6 km across, about 10% smaller
than Earth\'s Moon. It is made of silicates and has a layer of smooth
water ice 10 to 30 km thick. The ice has long cracks in it and very few
craters. It looks like the sea ice on Earth. The ice has slid around at
the cracks. We believe there is liquid water under the ice as much as
100 km below the surface. There are also some large spots on the
surface. In Roman mythology Europa was courted by Jupiter in the form of
a bull. Europa (Ancient Greek:Ευρώπη) in Greek mythology was a
Phoenician noblewoman who was abducted by Zeus to Crete (An island of
Greece).

### Ganymede

!Jupiter and its four largest moons, as seen through a
telescope.
Ganymede is 5262.4 km across, making it 380 km wider than Mercury. It is
Jupiter\'s largest moon and the largest moon in the Solar System. It has
**plate tectonics** like Earth. There are older, darker regions and
newer areas with grooves where the plates have moved. Newer craters have
bright rays around them from material thrown up by impacts. Older
craters look flat and faded because the icy surface does not hold the
shape of the crater as well as rock does over long periods of time.
Ganymede may have an iron and sulfur core with a silicate **mantle** and
an icy shell. It may be similar to Io except with a layer of ice on it.
In Roman mythology Ganymede was a beautiful young man who Jupiter
kidnapped and made cupbearer to the gods on Mt. Olympus.

### Callisto

!The orbit paths of the 4 largest
moons.
Callisto is 4820.6 km across, about the same size as Mercury. It has
many craters. Like craters on Ganymede, the older craters have faded.
The largest crater is *Valhalla*. It has a bright center 600 km across
with rings around it up to 3000 km across. Callisto is made of silicates
and ice. There is a 200 km thick icy **crust** with a liquid water sea
under it. In Roman mythology Callisto was turned into a bear by
Jupiter\'s jealous wife Juno. Later Jupiter placed her in the stars as
The Great Bear.

### Other moons

The other moons are smaller in several groups outside the orbits of the
major moons. There is also a small moon, Themisto and four groups of
small moons that orbit very far from Jupiter.

## How long is a day on this planet?

One Jupiter day is about 10 Earth hours long. You have to say \"about\"
because different parts of Jupiter rotate about its axis at different
speeds. This is caused by the fact that Jupiter is mostly gases that are
in constant motion and sometimes going in different directions. Some
efforts have been made to try and measure the rotation speed of the
inner rocky core of Jupiter, but that has proved to be quite difficult
to accomplish due to the magnetic fields that surround Jupiter and the
very active radio energy that is generated by the atmosphere of Jupiter,
which interferes with measuring techniques like radar that has been used
to measure the surface of Venus and Mars.

## How long is a year on Jupiter?

!The Great Red
Spot !Jupiter
Eclipses One year
on Jupiter is 4,335 Earth days or 11.87 Earth years long.

A Jupiter year is about equal to four-tenths (or two-fifths) of a Saturn
year. Thus after every two Saturn years, Jupiter has completed five full
orbits about the Sun. So after 59 years, Saturn and Jupiter will be back
in nearly the same position. When the orbits of two planets are simple
ratios of each other like this, it is called a **resonance**.\

## How much would Jupiter\'s gravity pull on me?

If someone were floating close to the cloud tops of Jupiter, it would
pull them down with a force about two and a half times as strong as the
force of Earth\'s gravity.

Jupiter\'s rapid rotation causes the equator to bulge out. This would
also cancel out about 10 percent of gravity\'s force on them if they
were at the equator. The amount of this counteraction becomes lower the
closer they get to the poles.

## Who is it named after?

!Statue of Zeus (Jupiter) in Olympia,
Greece in Olympia, Greece")

Jupiter (Latin *Iuppiter*) is named after the king of the Roman gods,
also called Zeus in ancient Greece. The god Jupiter was known for
causing lightning strikes on Earth. He is associated with the eagle and
the oak tree.

Next Topic: Saturn

شمسي/المشتري
bs:Wiki_junior_Sunčev_sistem/Jupiter
de:Wikijunior Sonnensystem/
Jupiter
es:Wikichicos/Sistema_Solar/Júpiter
nl:Wikijunior:Zonnestelsel/Jupiter
pl:Wikijunior:Układ_Słoneczny/Jowisz
fi:Wikijunior_Aurinkokunta/Jupiter
zh:Wikijunior:太阳系/木星