vania-janet/multiturn-rag-retrieval-data huggingface dataset:
Catalog of Earth Satellite Orbits
Just as the geosynchronous satellites have a sweet spot over the equator that lets them stay over one spot on Earth, the polar-orbiting satellites have a sweet spot that allows them to stay in one time. This orbit is a Sun-synchronous orbit, which means that whenever and wherever the satellite crosses the equator, the local solar time on the ground is always the same. For the Terra satellite for example, it’s always about 10:30 in the morning when the satellite crosses the equator in Brazil. When the satellite comes around the Earth in its next overpass about 99 minutes later, it crosses over the equator in Ecuador or Colombia at about 10:30 local time.

A Sun-synchronous orbit crosses over the equator at approximately the same local time each day (and night). This orbit allows consistent scientific observations with the angle between the Sun and the Earth’s surface remaining relatively constant. These illustrations show 3 consecutive orbits of a sun-synchronous satellite with an equatorial crossing time of 1:30 pm. The satellite’s most recent orbit is indicated by the dark red line, while older orbits are lighter red. View animation. (NASA illustration by Robert Simmon.)

The Sun-synchronous orbit is necessary for science because it keeps the angle of sunlight on the surface of the Earth as consistent as possible, though the angle will change from season to season. This consistency means that scientists can compare images from the same season over several years without worrying too much about extreme changes in shadows and lighting, which can create illusions of change. Without a Sun-synchronous orbit, it would be very difficult to track change over time. It would be impossible to collect the kind of consistent information required to study climate change.
The path that a satellite has to travel to stay in a Sun-synchronous orbit is very narrow. If a satellite is at a height of 100 kilometers, it must have an orbital inclination of 96 degrees to maintain a Sun-synchronous orbit. Any deviation in height or inclination will take the satellite out of a Sun-synchronous orbit.
Catalog of Earth Satellite Orbits
It is a good location for space telescopes, including the future James Webb Space Telescope (Hubble’s successor, scheduled to launch in 2014) and the current Wilkinson Microwave Anisotropy Probe (WMAP), used for studying the nature of the universe by mapping background microwave radiation.
The third Lagrange point is opposite the Earth on the other side of the Sun so that the Sun is always between it and Earth. A satellite in this position would not be able to communicate with Earth. The extremely stable fourth and fifth Lagrange points are in Earth’s orbital path around the Sun, 60 degrees ahead of and behind Earth. The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft will orbit at the fourth and fifth Lagrange points to provide a three-dimensional view of the Sun.

The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft took these images of sunspot 1024 on July 5, 2009, while on their way to L4 and L5. The perspectives of the Sun from 60 degrees behind (left) and ahead (right) of Earth’s orbit reveal portions of the Sun’s surface that would otherwise be hidden from view. (NASA images courtesy STEREO Science Center.)

Medium Earth Orbit
Closer to the Earth, satellites in a medium Earth orbit move more quickly. Two medium Earth orbits are notable: the semi-synchronous orbit and the Molniya orbit.
The semi-synchronous orbit is a near-circular orbit (low eccentricity) 26,560 kilometers from the center of the Earth (about 20,200 kilometers above the surface). A satellite at this height takes 12 hours to complete an orbit. As the satellite moves, the Earth rotates underneath it. In 24-hours, the satellite crosses over the same two spots on the equator every day. This orbit is consistent and highly predictable. It is the orbit used by the Global Positioning System (GPS) satellites.

The second common medium Earth orbit is the Molniya orbit. Invented by the Russians, the Molniya orbit works well for observing high latitudes.
Catalog of Earth Satellite Orbits
A satellite in a Molniya orbit takes 12 hours to complete its orbit, but it spends about two-thirds of that time over one hemisphere. Like a semi-synchronous orbit, a satellite in the Molniya orbit passes over the same path every 24 hours. This type of orbit is useful for communications in the far north or south.
Low Earth Orbit
Most scientific satellites and many weather satellites are in a nearly circular, low Earth orbit. The satellite’s inclination depends on what the satellite was launched to monitor. The Tropical Rainfall Measuring Mission (TRMM) satellite was launched to monitor rainfall in the tropics. Therefore, it has a relatively low inclination (35 degrees), staying near the equator.

TRMM’s low orbital inclination—just 35° from the equator—allows its instruments to concentrate on the tropics. This image shows one half of the observations TRMM makes in a single day. (NASA image courtesy TRMM Project.)

Many of the satellites in NASA’s Earth Observing System have a nearly polar orbit. In this highly inclined orbit, the satellite moves around the Earth from pole to pole, taking about 99 minutes to complete an orbit. During one half of the orbit, the satellite views the daytime side of the Earth. At the pole, satellite crosses over to the nighttime side of Earth.
As the satellites orbit, the Earth turns underneath. By the time the satellite crosses back into daylight, it is over the region adjacent to the area seen in its last orbit. In a 24-hour period, polar orbiting satellites will view most of the Earth twice: once in daylight and once in darkness.
Just as the geosynchronous satellites have a sweet spot over the equator that lets them stay over one spot on Earth, the polar-orbiting satellites have a sweet spot that allows them to stay in one time. This orbit is a Sun-synchronous orbit, which means that whenever and wherever the satellite crosses the equator, the local solar time on the ground is always the same. For the Terra satellite for example, it’s always about 10:30 in the morning when the satellite crosses the equator in Brazil.
Catalog of Earth Satellite Orbits
Other orbital “sweet spots,” just beyond high Earth orbit, are the Lagrange points. At the Lagrange points, the pull of gravity from the Earth cancels out the pull of gravity from the Sun. Anything placed at these points will feel equally pulled toward the Earth and the Sun and will revolve with the Earth around the Sun.
Of the five Lagrange points in the Sun-Earth system, only the last two, called L4 and L5, are stable. A satellite at the other three points is like a ball balanced at the peak of a steep hill: any slight perturbation will push the satellite out of the Lagrange point like the ball rolling down the hill. Satellites at these three points need constant adjustments to stay balanced and in place. Satellites at the last two Lagrange points are more like a ball in a bowl: even if perturbed, they return to the Lagrange point.

Lagrange points are special locations where a satellite will stay stationary relative to the Earth as the satellite and the Earth revolve around the Sun. L1 and L2 are positioned above the day and night sides of the Earth, respectively. L3 is on the other side of the Sun, opposite the Earth. L4 and L5 are 60° ahead and behind the Earth in the same orbit. (NASA illustration by Robert Simmon.)

The Lagrange points nearest the Earth are about 5 times the distance from the Earth to the Moon. L1 is between the Sun and Earth, and always views the Earth’s daylight side. L2 is opposite the sun, always on the night side. (NASA illustration by Robert Simmon.)

The first Lagrange point is located between the Earth and the Sun, giving satellites at this point a constant view of the Sun. The Solar and Heliospheric Observatory (SOHO), a NASA and European Space Agency satellite tasked to monitor the Sun, orbits the first Lagrange point, about 1.5 million kilometers away from Earth.
The second Lagrange point is about the same distance from the Earth, but is located behind the Earth.
Catalog of Earth Satellite Orbits
It would be impossible to collect the kind of consistent information required to study climate change.
The path that a satellite has to travel to stay in a Sun-synchronous orbit is very narrow. If a satellite is at a height of 100 kilometers, it must have an orbital inclination of 96 degrees to maintain a Sun-synchronous orbit. Any deviation in height or inclination will take the satellite out of a Sun-synchronous orbit. Since the drag of the atmosphere and the tug of gravity from the Sun and Moon alter a satellite’s orbit, it takes regular adjustments to maintain a satellite in a Sun-synchronous orbit.

Achieving and Maintaining Orbit
Launch
The amount of energy required to launch a satellite into orbit depends on the location of the launch site and how high and how inclined the orbit is. Satellites in high Earth orbit require the most energy to reach their destination. Satellites in a highly inclined orbit, such as a polar orbit, take more energy than a satellite that circles the Earth over the equator. A satellite with a low inclination can use the Earth’s rotation to help boost it into orbit. The International Space Station orbits at an inclination of 51.6397 degrees to make it easier for the Space Shuttle and Russian rockets to reach it. A polar-orbiting satellite, on the other hand, gets no help from Earth’s momentum, and so requires more energy to reach the same altitude.

Satellites in low-inclination orbits can get an energy boost from the Earth’s rotation by being launched near the equator. The European Space Agency launches satellites into geostationary orbits from their facilities in French Guiana (left). On the other hand, high-inclination satellites don’t receive much benefit from equatorial launch sites. The Baikonur Cosmodrome (right), located at 49° north, is frequently used to launch satellites into polar and Molniya orbits, as well as to send astronauts and supplies to the International Space Station. [Photographs ©2008 ESA/CNES/ARIANESPACE/Activité Photo Optique Video CSG (left) and courtesy NASA (right).]

Maintaining Orbit
Once a satellite is in orbit, it usually takes some work to keep it there.
Catalog of Earth Satellite Orbits
(NASA illustration by Robert Simmon.)

The first Lagrange point is located between the Earth and the Sun, giving satellites at this point a constant view of the Sun. The Solar and Heliospheric Observatory (SOHO), a NASA and European Space Agency satellite tasked to monitor the Sun, orbits the first Lagrange point, about 1.5 million kilometers away from Earth.
The second Lagrange point is about the same distance from the Earth, but is located behind the Earth. Earth is always between the second Lagrange point and the Sun. Since the Sun and Earth are in a single line, satellites at this location only need one heat shield to block heat and light from the Sun and Earth. It is a good location for space telescopes, including the future James Webb Space Telescope (Hubble’s successor, scheduled to launch in 2014) and the current Wilkinson Microwave Anisotropy Probe (WMAP), used for studying the nature of the universe by mapping background microwave radiation.
The third Lagrange point is opposite the Earth on the other side of the Sun so that the Sun is always between it and Earth. A satellite in this position would not be able to communicate with Earth. The extremely stable fourth and fifth Lagrange points are in Earth’s orbital path around the Sun, 60 degrees ahead of and behind Earth. The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft will orbit at the fourth and fifth Lagrange points to provide a three-dimensional view of the Sun.

The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft took these images of sunspot 1024 on July 5, 2009, while on their way to L4 and L5. The perspectives of the Sun from 60 degrees behind (left) and ahead (right) of Earth’s orbit reveal portions of the Sun’s surface that would otherwise be hidden from view. (NASA images courtesy STEREO Science Center.)

Medium Earth Orbit
Closer to the Earth, satellites in a medium Earth orbit move more quickly. Two medium Earth orbits are notable: the semi-synchronous orbit and the Molniya orbit.
The semi-synchronous orbit is a near-circular orbit (low eccentricity) 26,560 kilometers from the center of the Earth (about 20,200 kilometers above the surface).
Notes on the Fact Sheets
Orbit eccentricity A measure of the circularity of the orbit, equal to  (aphelion - perihelion distance)/(2 x semi-major axis). For the Galilean satellites, the forced eccentricity is given.  For a circular orbit eccentricity = 0. Dimensionless.Sidereal rotation period (hrs) The time for one rotation of the body on its axis  relative to the fixed stars, in hours. A minus sign  indicates retrograde rotation.Length of day (hrs) The average time in hours for the Sun to move from the  noon position in the sky at a point on the equator back  to the same position, on Earth this defines a 24 hour day. Obliquity to orbit (deg) The angle between the body's equator and the body's orbital  plane, with north defined by the right-hand rule. (J2000)Inclination of equator (deg) The angle between the equator and orbital plane with north  defined as pole axis above (north of) the plane of the  solar system, also denoted as axial tilt. (J2000)  Observational Parameters Approximate values for the minimum and maximum distances of the planets from Earth. Orbits fluctuate over time, these values are calculated from the mean orbital elements for J2000 250 year fits and the current orbits referenced to Julian Date 2459000.5 (11 June 2020). The planetary diameter used is two times the volumetric mean radius. For Venus, Jupiter, Saturn, Uranus, and Neptune, diameter is approximately to the visible cloud tops.  Mean orbital elements 250-year least squares fit elements referenced to J2000 (Global Earth Physics, p. 14)Longitude The point in a body's orbit around the Sun, defined from  0 to 360 degrees. The 0 point of longitude is defined as  the first point of Aries. This is the position of the Sun  as seen from Earth at Earth's vernal equinox, so at the  vernal equinox the Earth is at a longitude of 180 degrees.
Catalog of Earth Satellite Orbits
(NASA illustration courtesy Orbital Debris Program Office.)

The debris field generated by the Iridium collision is of particular concern to the Earth Observing System because the center of the debris field will eventually drift through the EOS satellites’ orbits. The Iridium and Russian satellites were 790 kilometers above the Earth, while EOS satellites orbit at 705 kilometers. Many pieces of debris from this collision were propelled to lower altitudes and are already causing issues at 705 kilometers.
Mission control engineers track orbital debris and other orbiting satellites that could come into the Earth Observing System’s orbit, and they carefully plan avoidance maneuvers as needed. The same team also plans and executes maneuvers to adjust the satellite’s inclination and height. The team evaluates these planned maneuvers to ensure that they do not bring the EOS satellites into close proximity to catalogued orbital debris or other satellites. To peek in on a day in the mission control center during one such maneuver, see the related article Flying Steady: Mission Control Tunes Up Aqua’s Orbit.

Links
J-Track 3-D
Eyes on the Earth 3D

References
Air University. (2003, August). Orbital Mechanics. Space Primer. Accessed May 22, 2009.
Blitzer, L. (1971, August). Satellite orbit paradox: A general view. American Journal of Physics. 39, 882-886.
Cornish, N. J. (2008). The Lagrange Points. Wilkinson Microwave Anisotropy Probe (WMAP), National Aeronautics and Space Administration. Accessed June 4, 2009.
European Space Agency. (2009, February 12). What are Lagrange Points? Accessed June 4, 2009.
Gleick, J. (2003). Isaac Newton. New York: Vintage Books.
Hawking, S. (2004). The Illustrated on the Shoulders of Giants. Philadelphia: Running Press.
Iannotta, B. and Malik, T. (2009, February 11). U.S. satellite destroyed in space collision. Accessed May 22, 2009.
The James Webb Space Telescope. About JWST’s Orbit.
What Is an Exoplanet? | NASA Space Place – NASA Science for Kids
What Is an Exoplanet? | NASA Space Place – NASA Science for Kids

all-about-exoplanets

Vea en Español

Earth
Sun
Solar System
Universe
Science and Tech
Educators

What Is an Exoplanet?

The Short Answer:

	All of the planets in our solar system orbit around the Sun. Planets that orbit around other stars are called exoplanets.
	

All of the planets in our solar system orbit around the Sun. Planets that orbit around other stars are called exoplanets. Exoplanets are very hard to see directly with telescopes. They are hidden by the bright glare of the stars they orbit.
So, astronomers use other ways to detect and study these distant planets. They search for exoplanets by looking at the effects these planets have on the stars they orbit.

An artist's representation of Kepler-11, a small, cool star around which six planets orbit.
Credit: NASA/Tim Pyle

How do we look for exoplanets?
One way to search for exoplanets is to look for "wobbly" stars. A star that has planets doesn’t orbit perfectly around its center. From far away, this off-center orbit makes the star look like it’s wobbling.

An orbiting planet (small blue ball) causes a star (large yellow ball) to orbit slightly off-center. From a distance, this makes it look like the star is wobbling.

Hundreds of planets have been discovered using this method. However, only big planets—like Jupiter, or even larger—can be seen this way. Smaller Earth-like planets are much harder to find because they create only small wobbles that are hard to detect.

How can we find Earth-like planets in other solar systems?
In 2009, NASA launched a spacecraft called Kepler to look for exoplanets. Kepler looked for planets in a wide range of sizes and orbits. And these planets orbited around stars that varied in size and temperature.
Some of the planets discovered by Kepler are rocky planets that are at a very special distance from their star.
How Does GPS Work? | NASA Space Place – NASA Science for Kids
How Does GPS Work? | NASA Space Place – NASA Science for Kids

gps-pizza

Earth
Sun
Solar System
Universe
Science and Tech
Educators

How Does GPS Work?

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It’s Friday night and you want some pizza. Fast. But somebody is going to have to pick that pizza up, and that means they need to know how to get to the closest pizzeria.
In this modern world that is no problem! Just plug ‘pizza’ into a smartphone and it tells you exactly how to get there.
But how exactly does the phone know where you are?
Something called a Global Positioning System, or GPS, tells you, that’s how.
When your phone tells you where you are, it may actually be listening to signals from satellites high up in space. There are over 30 satellites used for GPS, orbiting over 16,000 miles (26,000km) above the Earth!
Your phone just needs to figure out how far away you are from some of them.
If your phone knows how far away it is from four satellites, then there is only one place on Earth you can be!
Your phone, or any device with a GPS, is programmed to know where all the satellites are at any given time.
The phone uses that information—along with the amount of time the signal took to reach it—to figure out how far away the satellites are. By doing that, it computes its location.
So when you search for the nearest pizza place in your smartphone, this is what your phone is thinking:
“What satellites are talking to me right now?
Hey there, satellites! I know you guys! And I know where you are in the sky right now, too!
Let me listen to your signal to figure out how far away I am from each of you…
Oh! I must be right here!
Glossary - NASA Science
Below are some of the more common words and phrases you might run across.Exoplanet:A planet orbiting a star other than our Sun; also called “extrasolar planet.”Habitable zone:The range of orbital distance from a star at which temperatures would allow liquid water to exist on the surface of a planet with sufficient atmosphere. This range of distance changes depending on the size and temperature of the star. Earth is in the habitable zone of the Sun, one of the reasons our planet has liquid water like oceans and lakes.Goldilocks zone:An alternative name for “habitable zone” (see above), from the children’s story, “Goldilocks and the Three Bears.”Terrestrial:Planets composed mostly of rock (silicates) and metals, like Earth, Venus, Mars, and Mercury. Sometimes also called “rocky” or “telluric.”Tidally locked:When a celestial body, such as a planet or moon, always has one side facing the body it orbits, such as a star or planet. A tidally-locked planet has a day side facing the heat of its star, and a colder night side facing away. Tidal forces and the star’s gravity “lock” the planet, so that its orbital period is equal to its rotation period.Red dwarf star or M dwarf star:A class of small, relatively cool stars, emitting dim, red light. They are the most common type of star, comprising about 75 percent of all stars in the galaxy.Light-year:The distance light travels in one year, about 5.88 trillion miles (about 9.5 trillion kilometers).AU:An astronomical unit – the distance between Earth and the Sun, or about 93 million miles (150 million kilometers).Super-Earth:One of the most common types of exoplanets discovered so far, with a mass between that of Earth and Neptune. The properties of such planets are largely unknown.Orbit:The curving, repeating path of an object, such as a satellite, moon or planet, around a space body such as a moon, planet or star.Infrared:Electromagnetic radiation with wavelengths longer than the red end of the visible light spectrum, but shorter than microwaves.Transit:When an exoplanet crosses the face of its star from the perspective of Earthbound observers.
Imagine the Universe!
A class of galaxies which spew massive amounts of energy from their centers, far more than ordinary galaxies. Many astronomers believe supermassive black holes may lie at the center of these galaxies and power their explosive energy output.

 Tell me about AGN!
 Tell me more about AGN!

angstrom
A unit of length equal to 0.00000001 centimeters. This may also be written as 1 x 10-8 cm (see scientific notation).
angular momentum
A quantity obtained by multiplying the mass of an orbiting body by its velocity and the radius of its orbit. According to the conservation laws of physics, the angular momentum of any orbiting body must remain constant at all points in the orbit, i.e., it cannot be created or destroyed. If the orbit is elliptical the radius will vary. Since the mass is constant, the velocity changes. Thus planets in elliptical orbits travel faster at perihelion and more slowly at aphelion. A spinning body also possesses spin angular momentum. 
apastron
The point of greatest separation between two stars which are in orbit around each other. See binary stars. Opposite of periastron.
aphelion
The point in its orbit where a planet is farthest from the Sun. Opposite of perihelion.
apoapsis
The point in an orbit when the two objects are farthest apart. Special names are given to this orbital point for commonly used systems: see apastron, aphelion, and apogee.
apogee
The point in its orbit where an Earth satellite is farthest from the Earth. Opposite of perigee.
arc minute
An angular measurement equal to 1/60th of a degree.
arc second
An angular measurement equal to 1/60th of an arc minute or 1/3600th of a degree.
Ariel V
A UK X-ray mission, also known as UK-5

 Tell me more about Ariel V.

ASCA
The Japanese Asuka spacecraft (formerly Astro-D), an X-ray mission 

 Tell me more about ASCA.

ASD
Astrophysics Science Division, located at NASA's Goddard Space Flight Center.