Which spiral arm of the Milky Way contains our sun? | Space | EarthSky Which spiral arm of the Milky Way contains our sun? By Deborah Byrd in Space | May 20, 2014 Many know our Milky Way is a spiral galaxy. But where within this vast spiral structure do our sun and Earth reside? We live in an island of stars called the Milky Way, and many know that our Milky Way is a spiral galaxy. In fact, it’s a barred spiral galaxy , which means that our galaxy probably has just two major spiral arms, plus a central bar that astronomers are only now beginning to understand. But where within this vast spiral structure do our sun and its planets reside? Our galaxy is about 100,000 light-years wide. We’re about 25,000 light-years from the center of the galaxy. It turns out we’re not located in one of the Milky Way’s two primary spiral arms. Instead, we’re located in a minor arm of the galaxy. Our local spiral arm is sometimes Orion Arm, or sometimes the Orion Spur. It’s between the Sagittarius and Perseus Arms of the Milky Way. The image below shows it.

Our sun is located the Orion Arm, or Orion Spur, of the Milky Way galaxy. It’s a minor spiral arm, located between two other arms. Image updated in 2010 by R. Hurt on Wikimedia Commons. Our local Orion Arm of the Milky Way is some 3,500 light years across. It’s approximately 10,000 light years in length. Our sun, the Earth, and all the other planets in our solar system reside within this Orion Arm. We’re located close to the inner rim of this spiral arm, about halfway along its length. The Orion Arm, or Orion Spur, has other names as well. It’s sometimes simply called the Local Arm, or the Orion-Cygnus Arm, or the Local Spur. The Orion Arm is named for the constellation Orion the Hunter, which is one of the most prominent constellations of Northern Hemisphere winter (Southern Hemisphere summer). Some of the brightest stars and most famous celestial objects of this constellation (Betelgeuse, Rigel, the stars of Orion’s Belt, the Orion Nebula) are neighbors of sorts to our sun, located within the Orion Arm.

That’s why we see so many bright objects within the constellation Orion – because when we look at it, we’re looking into our own local spiral arm . HubbleSite - Reference Desk - FAQs Reference Desk Frequently Asked Questions What is a galaxy? A galaxy is an enormous collection of gas, dust and billions of stars held together by gravity. One galaxy can have hundreds of billions of stars and be as large as 200,000 light years across. What is the name of our galaxy? The name of our galaxy is the Milky Way. Our Sun and all of the stars that you see at night belong to the Milky Way. When you go outside on a dark night and look up, you will see a milky, misty-looking band stretching across the sky. When you look at this band, you are looking into the densest parts of the Milky Way, the "disk" and the "bulge." Where is the Earth in the Milky Way galaxy? Our solar system is at the edge of a spiral arm called the Orion Arm, and is about two-thirds of the way from the center of our galaxy to the edge of the starlight. The Earth is the third planet from the sun in our solar system of nine planets.

What is the closest galaxy like our own, and how far away is it? The closest spiral galaxy is Andromeda, a galaxy much like our own Milky Way. It is 2.2 million light years away from us. Andromeda is approaching our galaxy at a rate of 670,000 miles per hour (1,078,260 kph). Five billion years from now it will probably collide with our Milky Way galaxy. What are the parts of a galaxy? A galaxy contains stars, gas and dust. In a spiral galaxy like the Milky Way, the stars, gas, and dust are organized into a "bulge," a "disk" containing "spiral arms," and a "halo." Elliptical galaxies have a bulge-like central region and a halo, but do not have a disk. Bulge The bulge is a round structure made primarily of old stars, gas, and dust. The outer parts of the bulge are difficult to distinguish from the halo. The bulge of the Milky Way is roughly 10,000 light years across. Disk The disk is a flattened region that surrounds the bulge in a spiral galaxy.

The disk is shaped like a pancake. The Milky Way's disk is 100,000 light years across and 1,000 light years thick. It contains mostly young stars, gas and dust, which are concentrated in spiral arms. Some old stars are also present. Spiral Arms The spiral arms are curved extensions that begin at the bulge of a spiral galaxy, giving it a "pinwheel" appearance. Spiral arms contain a lot of gas and dust as well as young blue stars. Spiral arms are found only in spiral galaxies. Halo The halo primarily contains individual old stars and clusters of old stars ("globular clusters"). The halo also contains "dark matter," which is material that we cannot see but whose gravitational force can be measured. The Milky Way's halo may be over 130,000 light years across. Stars, gas, and dust Stars come in a variety of types. Blue stars, which are very hot, tend to have shorter lifetimes than red stars, which are cooler. Regions of galaxies where stars are currently forming are therefore bluer than regions where there has been no recent star formation.

Spiral galaxies seem to have a lot of gas and dust, while elliptical galaxies have very little gas or dust. How are galaxies classified? Astronomer Edwin Hubble classified galaxies into four major types: spiral, barred spiral, elliptical and irregular. Most of the nearby, bright galaxies are spirals, barred spirals or ellipticals. Spiral galaxies have a bulge at the center and a flattened disk containing spiral arms. Spiral galaxies have a variety of shapes and are classified according to the size of the bulge and the tightness and appearance of the arms. The spiral arms, which wrap around the bulge, contain numerous young blue stars and lots of gas and dust. Stars in the bulge tend to be older and redder. Yellow stars like our Sun are found throughout the disk of a spiral galaxy. The disks of spiral galaxies rotate somewhat like a hurricane or a whirlpool. Barred spiral galaxies are spiral galaxies that have a bar-shaped collection of stars running across the center of the galaxy. Elliptical galaxies do not have a disk or arms. Instead, they are characterized by a smooth, oval-shaped appearance. Ellipticals contain old stars, and possess little gas or dust.

They are classified by the shape of the ball, which can range from round to oval (baseball-shaped to football-shaped). In contrast to the disks of spirals, the stars in ellipticals do not all revolve around the center in an organized way. The stars move on randomly oriented orbits within the galaxy, like a swarm of bees. Irregular galaxies are galaxies that are neither spiral nor elliptical. They tend to be smaller objects that are without definite shape, and tend to have very hot newer stars mixed in with lots of gas and dust. Galaxy names are identified by a group of letters and numbers. What do they stand for? The letters indicate the catalog listing of the galaxies. Galaxies are listed in several different catalogs. The most common catalog is NGC, which stands for New General Catalog. Other catalogs include M (Messier), ESO (European Southern Observatory), IRAS (Infrared Astronomical Satellite), Mrk (Markarian), and UGC (Uppsala General Catalog). The numbers following the letters, such as Mrk 917 or NGC1433, indicate a galaxy’s entry in the catalog and are often related to the galaxy’s relative position in the sky.

Sometimes a galaxy appears in more than one catalog and can have more than one name. Why do astronomers study galaxies in ultraviolet light? Galaxies emit all kinds of electromagnetic radiation, from x-rays to radio waves. From this "light," astronomers get a clear picture of what these galaxies look like. But very distant galaxies pose a special problem. Light from these galaxies travels great distances (billions of light-years) to reach Earth. During its journey, the light is "stretched" due to the expansion of space. As a result, much of the light from the most distant galaxies is no longer visible, but has been shifted to the infrared where present instruments are less sensitive. The only light now in the visible region of the spectrum comes from regions where hot, young stars reside. These stars emit mostly ultraviolet light. But because this light has been stretched, it appears as visible light by the time it reaches Earth. Studying these distant galaxies is like trying to put together a puzzle with some of the pieces missing. So, astronomers are studying nearby galaxies in ultraviolet light to compare their shapes with those of their distant relatives. What are colliding galaxies? When two galaxies are close enough, their gravitational attraction draws them to each other.

That attraction increases as the galaxies move closer. The Milky Way and Andromeda are examples of two galaxies that will probably eventually collide (no sooner than 5 billion years in the future). In a direct encounter between two massive spiral galaxies such as these, huge cold clouds of molecules (gas) will be compressed, and millions of new stars will burst into life like a string of lights. As the galaxies first swing by each other, their once orderly disks will become jumbled with dust, gas, and brilliant blue star clusters. Then the galaxies may do a slow, graceful U-turn and plunge into each other. This second encounter will trigger another burst of star formation, which will drive the remaining gas and dust from the combined system. As the stars settle into randomly oriented orbits, the resulting system may take on an elliptical appearance. How do astronomers measure the distances to galaxies? Astronomers measure the distance to a galaxy in the same way we estimate the distance to an oncoming car by the brightness of its headlights. We know from experience how much light a car's headlights emits, so we can determine how far away the car is. To measure the distance to a galaxy, we try to find stars in that galaxy whose absolute light output we can measure.

We can then determine how far away the galaxy is by observing the brightness of the stars. Such stars can help us measure the distance to galaxies 300 million light years away. If a galaxy is too far away for us to distinguish individual stars, astronomers can use supernovae in the same manner, because the light output of supernovae at their peak brightness is a known fact. Supernovae can be used to measure the distance to galaxies as far as 10 billion light years away. Who is Edwin P. Hubble and what has he to do with galaxies? Edwin P. Hubble revolutionized cosmology by proving that the clouds of light astronomers saw in the night sky were actually other galaxies beyond our Milky Way. His greatest discovery was in 1929, when he identified the relationship between a galaxy's distance and the speed with which it is moving. The farther a galaxy is from Earth, the faster it is moving away from us. This is known as Hubble's Law. He also constructed a method of classifying the different shapes of galaxies. Edwin Powell Hubble was born in Marshfield, Missouri.

In 1910, he received his undergraduate degree from the University of Chicago and studied law under a Rhodes Scholarship at Oxford University. His true love, however, was astronomy, and he returned to the University of Chicago to earn a Ph.D. in that subject and work at the Yerkes Observatory. He served in the infantry during World War I. He once said that he "chucked the law for astronomy," knowing that even if he was second-rate or third-rate, it was astronomy that mattered. HubbleSite and STScI are not responsible for content found outside of hubblesite.org and stsci.edu Return to question list for Galaxies What Galaxy is the Earth In? - Universe Today Universe Today What Galaxy is the Earth In? Article Updated: 24 Dec , 2015 by Fraser Cain [/caption] Were you wondering what galaxy is the Earth in? You’ll probably recognize the answer: it’s the Milky Way Galaxy. If you go to a dark spot, away from the bright city lights, and look up, you should be able to see the Milky Way as a cloudy band stretching across the sky. It really does look like spilt milk spread across the sky.

But if you take a telescope and examine it more closely, you’ll see that the clouds are actually the collective light from thousands of stars. Since we’re embedded inside the Milky Way, we’re seeing our home galaxy edge-on, from the inside. To get a better idea, grab a dinner plate and take a look at it edge on, so you can’t see the circular shape of the galaxy. You can only see the edge of the plate. The Milky Way is an example of a barred spiral galaxy. It measures approximately 100,000 light years across and it’s only 1,000 light years thick; although, it’s more thick at the core where the galaxy bulges out. If you could fly out of the Milky Way in a rocket and then look back, you’d see a huge spiral shaped galaxy with a bar at the center. At the ends of this bar, there are two spiral arms which twist out forming the structure of the Milky Way. The Earth is located in the Solar System, and the Solar System is located about 25,000 light-years away from the core of the galaxy.

This also means that we’re about 25,000 light-years away from the outer edge of the Milky Way. We’re located in the Orion Spur, which is a minor arm located in between the two major galactic arms. If you’d like more information on the Milky Way, check out NASA’s Starchild info on the Milky Way , and here’s more info from the WMAP mission . We’ve written many articles about the Milky Way for Universe Today. Here’s an article with facts about the Milky Way , and here is a map of the Milky Way . We’ve also recorded several episodes of Astronomy Cast about the Milky Way. Listen here, Episode 99: The Milky Way . Galaxies, Galaxy Information, Galaxy Facts, News, Photos -- National Geographic Space A composite image of the Messier 81 (M81) galaxy shows what astronomers call a "grand design" spiral galaxy, where each of its arms curls all the way down into its center. Located about 12 million light-years away in the Ursa Major constellation, M81 is among the brightest of the galaxies visible by telescope from Earth.

Photograph courtesy NASA/JPL-Caltech/ESA/Harvard-Smithsonian CfA Galaxies are sprawling space systems composed of dust, gas, and countless stars. The number of galaxies cannot be counted—the observable universe alone may contain 100 billion. Some of these distant systems are similar to our own Milky Way galaxy, while others are quite different. Galaxies with less than a billion stars are considered "small galaxies." In our own galaxy, the sun is just one of about 100 billion stars. Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies, such as the Milky Way, consist of a flat disk with a bulging center and surrounding spiral arms. The galaxy's disk includes stars, planets, dust, and gas—all of which rotate around the galactic center in a regular manner. This spinning motion, at speeds of hundreds of kilometers per second, may cause matter in the disk to take on a distinctive spiral shape like a cosmic pinwheel. Some spiral galaxies obtain even more interesting shapes that earn them descriptive names, such as sombrero galaxies. Older stars reside in the bulge at the center of the galactic disk.

Many new stars also form in spiral systems, and their disks are surrounded by a halo, which scientists believe is rich with mysterious dark matter. Elliptical galaxies are shaped as their name suggests. They are generally round but stretch longer along one axis than along the other. They may be nearly circular or so elongated that they take on a cigarlike appearance. Elliptical galaxies contain many older stars, up to one trillion, but little dust and other interstellar matter. Their stars orbit the galactic center, like those in the disks of spiral galaxies, but they do so in more random directions. Few new stars are known to form in elliptical galaxies. The universe's largest known galaxies are giant elliptical galaxies, which may be as much as two million light-years long. Elliptical galaxies may also be small, in which case they are dubbed dwarf elliptical galaxies. Galaxies that are not spiral or elliptical are called irregular galaxies. Irregular galaxies appear misshapen and lack a distinct form, often because they are within the gravitational influence of other galaxies close by. Galactic Mergers Some galaxies occur alone or in pairs, but they are more often parts of larger associations known as groups, clusters, and superclusters.

Galaxies in such groups often interact and even merge together in a dynamic cosmic dance of interacting gravity. Mergers cause gases to flow towards the galactic center, which can trigger phenomena like rapid star formation. Our own Milky Way may someday merge with the Andromeda galaxy—just two million light-years away and visible to the naked eye from Earth's Northern Hemisphere. These intergalactic processes may be part of natural evolution by which irregular galaxies transform into one of the other shapes, and by which spiral galaxies eventually become elliptical galaxies—as scientists believe they must. Galaxy Origins Most astronomers suggest that galaxies formed shortly after a cosmic "big bang" that began the universe some 10 billion to 20 billion years ago. In the milliseconds following this explosion, clouds of gases began to coalesce, collapse, and compress under gravity to form the building blocks of galaxies. Scientists are divided on just how galaxies first formed. Some believe that smaller clusters of about one million stars, known as globular clusters, formed first and later gathered into galaxies. Others believe that galaxies formed first and that only later did the stars within them begin to gather into smaller clusters.

BBC Universe - The Andromeda galaxy is our galactic neighbour Listen now 45 min Melvyn Bragg and guests discuss the creation and destruction of galaxies. Melvyn Bragg and guests discuss the galaxies; spread out across the void of space like spun sugar, but harbouring in their centres super-massive black holes. About Andromeda galaxy The Andromeda Galaxy (/ænˈdrɒmᵻdə/), also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth. It is the nearest major galaxy to the Milky Way and was often referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. Andromeda is approximately 220,000 light years across, and it is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and other smaller galaxies.

Despite earlier findings that suggested that the Milky Way contains more dark matter and could be the largest in the grouping, the 2006 observations by the Spitzer Space Telescope revealed that Andromeda contains one trillion (1012) stars: at least twice the number of stars in the Milky Way, which is estimated to be 200–400 billion. The mass of the Andromeda Galaxy is estimated to be 1.5×1012solar masses, while the Milky Way is estimated to be 8.5×1011 solar masses. The Milky Way and Andromeda galaxies are expected to collide in 4.5 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy. The apparent magnitude of the Andromeda Galaxy, at 3.4, is among the brightest of the Messier objects, making it visible to the naked eye on moonless nights, even when viewed from areas with moderate light pollution. New Galactic Supercluster Map Shows Milky Way's 'Heavenly' Home New Galactic Supercluster Map Shows Milky Way's 'Heavenly' Home By Charles Q.

Choi , Space.com Contributor | September 3, 2014 01:01pm ET MORE Scientists have created the first map of a colossal supercluster of galaxies known as Laniakea, the home of Earth's Milky Way galaxy and many other. This computer simulation, a still from a Nature journal video, depicts the giant supercluster, with the Milky Way's location shown as a red dot. Credit: Nature Video A new cosmic map is giving scientists an unprecedented look at the boundaries for the giant supercluster that is home to Earth's own Milky Way galaxy and many others. Scientists even have a name for the colossal galactic group: Laniakea, Hawaiian for "immeasurable heaven." The scientists responsible for the new 3D map suggest that the newfound Laniakea supercluster of galaxies may even be part of a still-larger structure they have not fully defined yet. "We live in something called ' the cosmic web ,' where galaxies are connected in tendrils separated by giant voids," said lead study author Brent Tully, an astronomer at the University of Hawaii at Honolulu.

This computer-generated depiction of the Laniakea Supercluster of galaxies, which includes the Milky Way galaxy containing Earth's solar system, shows a view of the supercluster as seen from the supergalactic equatorial plane. Credit: SDvision interactive visualization software by DP at CEA/Saclay, France Galactic structures in space Galaxies are not spread randomly throughout the universe. Instead, they clump in groups, such as the one Earth is in, the Local Group, which contains dozens of galaxies. In turn, these groups are part of massive clusters made up of hundreds of galaxies, all interconnected in a web of filaments in which galaxies are strung like pearls. The colossal structures known as superclusters form at the intersections of filaments. The giant structures making up the universe often have unclear boundaries. To better define these structures, astronomers examined Cosmicflows-2, the largest-ever catalog of the motions of galaxies, reasoning that each galaxy belongs to the structure whose gravity is making it flow toward. "We have a new way of defining large-scale structures from the velocities of galaxies rather than just looking at their distribution in the sky," Tully said.

Laniakea, our home in the universe Two views of the Laniakea Supercluster, a massive collection of galaxies that contains Earth's Milky Way galaxy and many others, are shown in these computer-generated images. Credit: SDvision interactive visualization software by DP at CEA/Saclay, France The new 3D map developed by Tully and colleagues shows that the Milky Way galaxy resides in the outskirts of the Laniakea Supercluster, which is about 520 million light-years wide. The supercluster is made up of about 100,000 galaxies with a total mass about 100 million billion times that of the sun. [ How Computers Simulate the Universe (Infographic) ] The name Laniakea was suggested by Nawa'a Napoleon, who teaches Hawaiian language at Kapiolani Community College in Hawaii. The name is meant to honor Polynesian navigators who used their knowledge of the heavens to make long voyages across the immensity of the Pacific Ocean. "We live in the Local Group, which is part of the Local Sheet next to the Local Void — we wanted to come up with something a little more exciting than 'Local,'" Tully told Space.com.

This supercluster also includes the Virgo cluster and Norma-Hydra-Centaurus, otherwise known as the Great Attractor. These new findings help clear up the role of the Great Attractor, which is a problem that has kept astronomers busy for 30 years. Within the Laniakea Supercluster, the motions of galaxies are directed inward, as water flows in descending paths down a valley, and the Great Attractor acts like a large flat-bottomed gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster. Tully noted Laniakea could be part of an even larger structure. "We probably need to measure to another factor of three in distance to explain our local motion," Tully said. "We might find that we have to come up with another name for something larger than we're a part of — we're entertaining that as a real possibility." Follow us @Spacedotcom , Facebook and Google+ . Original article on Space.com .

Editor's Recommendations All about the Andromeda galaxy | Clusters Nebulae Galaxies | EarthSky All about the Andromeda galaxy By Bruce McClure in Clusters Nebulae Galaxies | September 15, 2016 At 2.3 million light-years, the Andromeda galaxy is the closest spiral galaxy to our Milky Way and the most distant thing you can see with your eye alone. Josh Blash captured this image of the Andromeda galaxy. Although a couple of dozen minor galaxies lie closer to our Milky Way, the Andromeda galaxy is the closest major galaxy to ours. Excluding the Large and Small Magellanic Clouds, which can’t be seen from northerly latitudes, the Andromeda galaxy – also known as M31 – is the brightest galaxy in all the heavens. It’s the most distant thing you can see with your unaided eye, at 2.3 million light-years . To the eye, it appears as a smudge of light larger than a full moon. Follow the links below to learn more about the Andromeda galaxy.

Andromeda and Milky Way in context Earthsky friend Thomas Wildoner, caught the Andromeda galaxy in August 2014. When to look for the Andromeda Galaxy. From mid-northern latitudes, you can see M31 – also called the Andromeda galaxy – for at least part of every night, all year long. But most people see the galaxy first in northern autumn, when it’s high enough in the sky to be seen from nightfall till daybreak. In late September and early October, the Andromeda galaxy shines in your eastern sky at nightfall, swings high overhead around midnight (1 a.m. daylight saving time) and stands rather high in the west at the onset of morning dawn. Winter evenings are also good for viewing the Andromeda galaxy. If you are far from city lights, and it’s a moonless night – and you’re looking on an autumn or winter evening – it’s possible you’ll simply notice the galaxy in your night sky. It’s looks like a hazy patch in the sky, as wide across as a full moon.

But if you look, and don’t see the galaxy – yet you know you’re looking at a time when it’s above the horizon – you can star-hop to find the galaxy in one of two ways. First, you can use the Great Square of Pegasus. Second, you can use the constellation Cassiopeia. Use the Great Square of Pegasus to find the Andromeda Galaxy. A line between Mirach and Mu Andromedae points to the galaxy. Find the Andromeda galaxy using the Great Square of Pegasus. You’ll be hopping to the Andromeda galaxy from the Great Square of Pegasus. In autumn, the Great Square of Pegasus looks like a great big baseball diamond in the eastern sky. Envision the bottom star of the Square’s four stars as home plate, then draw an imaginary line from the “first base” star though the “third base” star to locate two streamers of stars flying away from the Great Square. These stars belong to the constellation Andromeda the Princess. On each streamer, go two stars north (left) of the third base star, locating the stars Mirach and Mu Andromedae.

Draw a line from Mirach through Mu Andromedae, going twice the Mirach/Mu Andromedae distance. You’ve just landed on the Andromeda galaxy, which looks like a smudge of light to the unaided eye. If you can’t see the Andromeda galaxy with the eye alone, by all means use binoculars. Many people use the M- or W-shaped constellation Cassiopeia to find the Andromeda galaxy. See how the star Schedar points to the galaxy? Find the Andromeda galaxy using the constellation Cassiopeia. The constellation Cassiopeia the Queen is one of the easiest constellations to recognize. It is shaped like the letter M or W. Look generally northward on the sky’s dome to find this constellation. If you can recognize the north star, Polaris – and if you know how to find the Big Dipper – be aware that the Big Dipper and Cassiopeia move around Polaris like the hands of a clock, always opposite each other. To find the Andromeda galaxy via Cassiopeia, look for the star Schedar. In the illustration above, see how the star Schedar points to the galaxy?

Many people use the Cassiopeia to find the Andromeda galaxy, because Cassiopeia itself is so easy to spot. The Great Andromeda Nebula, photographed in the year 1900. At this point, astronomers could not discern individual stars in the galaxy. Many thought it was a cloud of gas within our Milky Way – a place where new stars were forming. Image via Wikimedia Commons. History of our knowledge of the Andromeda galaxy. At one time, the Andromeda galaxy was called the Great Andromeda Nebula. Astronomers thought this patch of light was composed of glowing gases, or was perhaps a solar system in the process of formation. It wasn’t until the 20th century that astronomers were able to resolve the Andromeda spiral nebula into individual stars. This discovery lead to a controversy about whether the Andromeda spiral nebula and other spiral nebulae lie within or outside the Milky Way. In the 1920s Edwin Hubble finally put the matter to rest, when he used Cepheid variable stars within the Andromeda galaxy to determine that it is indeed an island universe residing beyond the bounds of our Milky Way galaxy.

Artist’s illustration of our Local Group via Chandra X-Ray Observatory. Andromeda and Milky Way in context. The Andromeda galaxy and our Milky Way galaxy reign as the two most massive and dominant galaxies within the Local Group of Galaxies. The Andromeda Galaxy is the largest galaxy of the Local Group, which, in addition to the Milky Way, also contains the Triangulum Galaxy, and about 30 other smaller galaxies. Both the Milky Way and the Andromeda galaxies lay claim to about a dozen satellite galaxies. Both are some 100,000 light-years across, containing enough mass to make billions of stars. Astronomers have discovered that our Local Group is on the outskirts of a giant cluster of several thousand galaxies – which astronomers call the Virgo Cluster. We also know of an irregular supercluster of galaxies, which contains the Virgo Cluster, which in turn contains our Local Group, which in turn contains our Milky Way galaxy and the nearby and Andromeda galaxy. At least 100 galaxy groups and clusters are located within this Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

The Virgo Supercluster is thought to be one of millions of superclusters in the observable universe. The Andromeda Galaxy with two of its satellite galaxies, via Wikimedia Commons . Click here to expand. Bottom line: At 2.3 million light-years, the Great Andromeda galaxy (Messier 31) rates as one of the most distant objects you can see with the unaided eye. It is also the closest and brightest spiral galaxy to our Milky Way galaxy. This post tells how to find it, some of its history and gives some context for thinking about both our Milky Way galaxy and the Andromeda galaxy in the universe. The Andromeda galaxy (M31) is at RA: 0h 42.7m; Dec: 41o 16′ north Galaxies | Science Mission Directorate Science Mission Directorate Exoplanets Galaxies Our galaxy, the Milky Way , is typical: it has hundreds of billions of stars, enough gas and dust to make billions more stars, and at least ten times as much dark matter as all the stars and gas put together. And it’s all held together by gravity . Like more than two-thirds of the known galaxies, the Milky Way has a spiral shape .

At the center of the spiral, a lot of energy and, occasionally, vivid flares are being generated. Based on the immense gravity that would be required to explain the movement of stars and the energy expelled, the astronomers conclude that the center of the Milky Way is a supermassive black hole . Other galaxies have elliptical shapes, and a few have unusual shapes like toothpicks or rings. The Hubble Ultra Deep Field (HUDF) shows this diversity. Hubble observed a tiny patch of sky (one-tenth the diameter of the moon) for one million seconds (11.6 days) and found approximately 10,000 galaxies, of all sizes, shapes, and colors. From the ground, we see very little in this spot, which is in the constellation Fornax. High School Earth Science/Galaxies - Wikibooks, open books for an open world High School Earth Science/Galaxies 8 Points to Consider Compared to your neighborhood, your country, or even planet Earth, the solar system is an extremely big place. But there are even bigger systems in the universe; groups of two, two hundred, or two billion stars!

Small groups of stars are called star systems, and somewhat larger groups are called star clusters. There are even larger groups of stars, called galaxies. Our solar system is in the Milky Way Galaxy, which is just one galaxy in the universe. There are several different types of galaxies and there are possibly billions of galaxies in the universe. Distinguish between star systems and star clusters. Identify different types of galaxies. Describe our own galaxy, the Milky Way Galaxy. Star Systems and Star Clusters[ edit ] Constellations are patterns of stars that we see in the same part of the night sky, but these stars may not be close together at all out in space. However, some stars are actually grouped closely together in space. These small groups of stars are called star systems and larger groups of hundreds or thousands of stars are called star clusters. Star Systems[ edit ] Our solar system has only one star, the Sun. But many stars—in fact, more than half of the bright stars in our galaxy—are in systems of two or more stars. A system of two stars orbiting each other is called a binary star system. A system with more than two stars is called a multiple star system. In a multiple star system, each of the stars orbits around the others.

Often, the stars in a multiple star system are so close together that you can only tell there are multiple stars using binoculars or a telescope. Figure 26.7 shows Sirius A, the brightest star in the sky. Sirius A is a very large star. If you look to the lower left of Sirius A in the figure, you can see a much smaller star. This is Sirius B, a white dwarf companion to Sirius A. Figure 26.7: The bright star Sirius is actually a binary star system with one large star (Sirius A) and one small star (Sirius B). This image from the Hubble Space Telescope shows Sirius B to the lower left of Sirius A. As you might guess, Sirius A is much, much brighter than Sirius B. Sirius B once was brighter than its companion, but it became a red giant and collapsed into its current dim state about 100-125 million years ago. butt Star Clusters[ edit ] Star clusters are divided into two main types: open clusters and globular clusters. Open clusters are groups of up to a few thousand stars that are loosely held together by gravity.

The Pleiades, shown in Figure 26.8, is a well-known open cluster. The Pleiades are also called the Seven Sisters, because you can see seven stars in the cluster without a telescope, but with good vision. Using a telescope reveals that the Pleiades has close to a thousand stars. Figure 26.8: The Pleiades is an open cluster containing several hundred stars surrounded by gas. Note that the stars are mostly blue. Open clusters tend to be blue in color and often contain glowing gas and dust. That is because the stars in an open cluster are young stars that formed from the same nebula. Eventually, the stars may be pulled apart by gravitational attraction to other objects. Figure 26.9 shows an example of a globular cluster. Globular clusters are groups of tens to hundreds of thousands of stars held tightly together by gravity. Unlike open clusters, globular clusters have a definite, spherical shape. Globular clusters contain mostly old, reddish stars. As you get closer to the center of a globular cluster, the stars are closer together. Globular clusters don't have much dust in them—the dust has already formed into stars.

Figure 26.9: M80 is a large globular cluster containing hundreds of thousands of stars. Note that the cluster is spherical and contains mostly red stars. Types of Galaxies[ edit ] The biggest groups of stars are called galaxies. Galaxies can contain anywhere from a few million stars to many billions of stars. Every star you can see in the sky is part of the Milky Way Galaxy, the galaxy we live in. Other galaxies are extremely far away, much farther away than even the most distant stars you can see. The closest major galaxy—the Andromeda Galaxy, shown in Figure 26.10—looks like only a dim, fuzzy spot to the naked eye. But that fuzzy spot contains one trillion stars; that is a thousand billion, or 1,000,000,000,000 stars! Figure 26.10: The Andromeda Galaxy is the closest major galaxy to our own. Andromeda is a large spiral galaxy that contains about a trillion stars. Spiral Galaxies[ edit ] Galaxies are divided into three types according to shape: spiral galaxies, elliptical galaxies, and irregular galaxies.

Spiral galaxies rotate or spin, so they have a rotating disk of stars and dust, a bulge in the middle, and several arms spiraling out from the center. Spiral galaxies have lots of gas and dust and lots of young stars. Figure 26.11 shows a spiral galaxy from the side, so you can see the disk and central bulge. Figure 26.11: The Sombrero Galaxy is a spiral galaxy that we see from the side. Figure 26.12 shows a spiral galaxy face-on, so you can see the spiral arms. The spiral arms of a galaxy contain lots of dust. New stars form from this dust. Because they contain lots of young stars, spiral arms tend to be blue. Figure 26.12: The Pinwheel Galaxy is a spiral galaxy we see face-on. Note the blue spiral arms. Elliptical Galaxies[ edit ] Figure 26.13 shows a typical elliptical galaxy. As you might have guessed, elliptical galaxies are elliptical, or egg-shaped. The smallest elliptical galaxies are as small as some globular clusters. Giant elliptical galaxies, on the other hand, can contain over a trillion stars.

Elliptical galaxies are reddish to yellowish in color because they contain mostly old stars. Figure 26.13: The large, reddish-yellow object in the middle of this figure is a typical elliptical galaxy. Can you find other galaxies in the figure? What kind? Typically, elliptical galaxies contain very little gas and dust because the gas and dust has already formed into stars. However, some elliptical galaxies, like the one shown in Figure 26.14, contain lots of dust. Astronomers believe that these dusty elliptical galaxies form when two galaxies of similar size collide. Figure 26.14: This elliptical galaxy probably formed when two galaxies of similar size collided with each other. Irregular Galaxies and Dwarf Galaxies[ edit ] Look at the galaxy in Figure 26.15. Do you think this is a spiral galaxy or an elliptical galaxy? It is neither one! Galaxies that are not clearly elliptical galaxies or spiral galaxies are called irregular galaxies. Most irregular galaxies were once spiral or elliptical galaxies that were then deformed either by gravitational attraction to a larger galaxy or by a collision with another galaxy.

Figure 26.15: This galaxy, called NGC 1427A, is an irregular galaxy. It has neither a spiral nor an elliptical shape. Dwarf galaxies are small galaxies containing "only" a few million to a few billion stars. Most dwarf galaxies are irregular in shape. However, there are also dwarf elliptical galaxies and dwarf spiral galaxies. Dwarf galaxies are the most common type in the universe. However, because they are relatively small and dim, we don't see as many dwarf galaxies as we do their full-sized cousins. Look back at Figure 26.10. In the figure, you can see two dwarf elliptical galaxies that are companions to the Andromeda Galaxy. One is a bright sphere to the left of center, and the other is a long ellipse below and to the right of center. Dwarf galaxies are often found near larger galaxies. They sometimes collide with and merge into their larger neighbors. The Milky Way Galaxy[ edit ] If you look up in the sky on a very clear night, you may see a milky band of light stretching across the sky, as in Figure 26.16.

This band is called the Milky Way, and it consists of millions of stars along with a lot of gas and dust. This band is the disk of a galaxy, the Milky Way Galaxy, which is our galaxy. The Milky Way Galaxy looks different to us than other galaxies because we are actually living inside of it! Figure 26.16: The band of light called the Milky Way can be seen on a clear, dark night. Looking at this band, you are looking along the main disk of our galaxy. Shape and Size[ edit ] Because we live inside the Milky Way Galaxy, it is hard to know exactly what it looks like. But astronomers believe the Milky Way Galaxy is a typical spiral galaxy that contains about 100 billion to 400 billion stars. Figure 26.17 shows what our Galaxy would probably look like if seen from the outside. Figure 26.17: This artist's rendering shows what we currently think the Milky Way Galaxy would look like seen from above. The Sun and solar system (and you!) are a little more than halfway out from the center. Like other spiral galaxies, our galaxy has a disk, a central bulge, and spiral arms.

The disk is about 100,000 light-years across and 3,000 light-years thick. Most of the Galaxy's gas, dust, young stars, and open clusters are in the disk. The central bulge is about 12,000 to 16,000 light-years wide and 6,000 to 10,000 light-years thick. The central bulge contains mostly older stars and globular clusters. Some recent evidence suggests the bulge might not be spherical, but is instead shaped like a bar. The bar might be as long as 27,000 light-years long. The disk and bulge are surrounded by a faint, spherical halo, which also contains old stars and globular clusters. Some astronomers believe there is a gigantic black hole at the center of the Galaxy. The Milky Way Galaxy is a big place. If our solar system were the size of your fist, the Galaxy's disk would still be wider than the entire United States! Where We Are[ edit ] Our solar system, including the Sun, Earth, and all the other planets, is within one of the spiral arms in the disk of the Milky Way Galaxy.

Most of the stars we see in the sky are relatively nearby stars, that are also in this spiral arm. We are about 26,000 light years from the center of the Galaxy. In other words, we live a little more than halfway out from the center of the Galaxy to the edge. Just as Earth orbits the Sun, the Sun and solar system orbit the center of the Galaxy. One orbit of the solar system takes about 225 to 250 million years. The solar system has orbited 20 to 25 times since it formed 4.6 billion years ago. Most stars are in systems of two or more stars. Open clusters are groups of young stars loosely held together by gravity. Globular clusters are spherical groups of old stars held tightly together by gravity. Galaxies are collections of millions to many billions of stars. Spiral galaxies have a rotating disk of stars and dust, a bulge in the middle, and several arms spiraling out from the center. The disk and arms contain many young, blue stars. Typical elliptical galaxies are egg-shaped, reddish, and contain mostly old stars. Galaxies that are not elliptical or spiral galaxies are called irregular galaxies.

Often these galaxies were deformed by other galaxies. The band of light called the Milky Way is the disk of our galaxy, the Milky Way Galaxy, which is a typical spiral galaxy. Our solar system is in a spiral arm of the Milky Way Galaxy, a little more than halfway from the center to the edge of the disk. Most of the stars we see are in our spiral arm. What is a binary star system? Compare globular clusters with open clusters. Name the three main types of galaxies. List three main features of a spiral galaxy. Suppose you see a round galaxy that is reddish in color and contains very little dust. What kind of galaxy is it? What galaxy do we live in, and what kind of galaxy is it? Describe the location of our solar system in our galaxy. Earth's New Address Is...A Tiny Part Of The Laniakea Galactic Supercluster | Science 2.0 Earth's New Address Is...A Tiny Part Of The Laniakea Galactic Supercluster News Staff You have a new galactic address; astronomers have determined that our own Milky Way galaxy is part of a newly identified enormous supercluster of galaxies - dubbed "Laniakea," which means "immense heaven" in Hawaiian.

This discovery broadens the boundaries of our galactic neighborhood and establishes previously unrecognized linkages among various galaxy clusters in the local Universe. How big are are talking? The Milky Way galaxy alone has 100 billion stars. We think. And then there are 1012 galaxies. So your address is now a lot bigger. Instead of being Earth, Sol, Orion arm, Milky Way, Local Group and Virgo cluster, you can now add Laniakea before Universe. Superclusters are among the largest structures in the known Universe. They are made up of groups, like our own Local Group, that contain dozens of galaxies, and massive clusters that contain hundreds of galaxies, all interconnected in a web of filaments. Though these structures are interconnected, they have poorly defined boundaries. A slice of the Laniakea Supercluster in the supergalactic equatorial plane -- an imaginary plane containing many of the most massive clusters in this structure. The colors represent density within this slice, with red for high densities and blue for voids -- areas with relatively little matter. Individual galaxies are shown as white dots.

Velocity flow streams within the region gravitationally dominated by Laniakea are shown in white, while dark blue flow lines are away from the Laniakea local basin of attraction. The orange contour encloses the outer limits of these streams, a diameter of about 160 Mpc. This region contains the mass of about 100 million billion suns. Credit: SDvision interactive visualization software by DP at CEA/Saclay, France. To better refine cosmic mapmaking, the researchers are proposing a new way to evaluate these large-scale galaxy structures by examining their impact on the motions of galaxies. A galaxy between structures will be caught in a gravitational tug-of-war in which the balance of the gravitational forces from the surrounding large-scale structures determines the galaxy's motion. "We have finally established the contours that define the supercluster of galaxies we can call home," said lead researcher R. Brent Tully, an astronomer at the University of Hawaii at Manoa.

"This is not unlike finding out for the first time that your hometown is actually part of much larger country that borders other nations." By using the GBT and other radio telescopes to map the velocities of galaxies throughout our local Universe, the team was able to define the region of space where each supercluster dominates. "Green Bank Telescope observations have played a significant role in the research leading to this new understanding of the limits and relationships among a number of superclusters," said Tully. The Milky Way resides in the outskirts of one such supercluster, whose extent has for the first time been carefully mapped using these new techniques. This so-called Laniakea Supercluster is 500 million light-years in diameter and contains the mass of one hundred million billion Suns spread across 100,000 galaxies. This study also clarifies the role of the Great Attractor, a gravitational focal point in intergalactic space that influences the motion of our Local Group of galaxies and other galaxy clusters. Within the boundaries of the Laniakea Supercluster, galaxy motions are directed inward, in the same way that water streams follow descending paths toward a valley.

The Great Attractor region is a large flat bottom gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster. The name Laniakea was suggested by Nawa'a Napoleon, an associate professor of Hawaiian Language and chair of the Department of Languages, Linguistics, and Literature at Kapiolani Community College, a part of the University of Hawaii system. The name honors Polynesian navigators who used knowledge of the heavens to voyage across the immensity of the Pacific Ocean. Published in Nature.

Question: What is the name of the galaxy that contains the Earth?
Answer: Milky Way