Galaxies Facts

Galaxies ['gă -lək-sēz]

Millions or billions of stars held together by gravitational attraction.


Multiple galaxies at night

The universe is full of amazing and beautiful bodies. Some bodies are planets like the one we live on — Earth. Some objects are stars, burning balls of gas like our sun. There are moons, asteroids, comets, gas clouds, and black holes. Gravity pulls the stars and the other space bodies into groups. These collections of stars, planets, moons, asteroids, and other space bodies make up what is called a galaxy.

Galaxies are huge. They can contain millions and some even have trillions of stars. Most of the matter found in the universe is contained within one of the many galaxies. Scientists have no idea how many actual galaxies exist. There are so many that it is nearly impossible to count them all. Some are so far away or hidden behind dust clouds that scientists continue to work at identifying the many galaxies that exist.

Closest Galaxy

Milkyway Galaxy

Our sun is a rather small-sized star and just one of perhaps 400 billion stars in the Milky Way galaxy. The name 'Milky Way' comes from the Greek word Galaxios, which means milky circle. We live in the very edge of the Milky Way and so we can see our galaxy in the sky on a clear night. It indeed looks like a milky cluster of stars in a path above our heads.

The Mayans thought that path was the route to the underworld. Many other astronomers throughout time have observed the Milky Way and tried to explain its origin, its size, and its properties. Galileo studied the Milky Way with his early telescope. William Herschel attempted to map the Milky Way in 1785. It was Edwin Powell Hubble who in 1925 used a huge telescope to study the Milky Way and propose the existence of other galaxies. As scientists continue to study the Milky Way, they are discovering that it is far bigger than it was first thought.

Galaxy Types

Edwin Powell Hubble created a means of classifying galaxies based on their shape. There are four basic classifications with subgroups within those basic shapes.

Spiral Galaxies — Spiral galaxies are identified by their center nucleus and generally flat shape. Many have arms that spiral out from the nucleus. Our Milky Way is a spiral galaxy.

Andromeda galaxy

Barred Spiral Galaxies — Barred spiral galaxies are similar to spiral galaxies except that the arms lead out from a series of stars and not from the center.

Barred spiral galaxy
Image courtesy of ESA/Hubble & NASA

Elliptical Galaxies — Elliptical galaxies can range from round to oval, but have no center bulge like spiral galaxies do.

Elliptical galaxy

Irregular galaxies — Irregular galaxies tend to be very irregular in shape and can look like a cloud or a gassy mass.

How do galaxies get their names?

Sombrero Galaxy
Sombrero Galaxy

Many galaxies have been given names based on their discoverer or their shape. The Magellan Clouds were named by Magellan's crew who saw them during their first trip around the world in 1519. The Sombrero galaxy was called such because it resembles a sombrero. Other galaxies have been designated by a catalogue of numbers. Catalogues have been created by scientists and observatories as new galaxies are discovered.

Top 10 Questions

September 2012

Thanks to Dr. Amber Straughn, Research Astrophysicist at the Goddard Space Flight Center, NASA and Deputy Project Scientist for James Webb Space Telescope Education and Public Outreach for the answers.

  1. Can other galaxies support human life?

    Nobody knows for sure. There are about 100 billion stars in our Milky Way, and about 100 billion other galaxies. Many of those stars have planets, but it takes a lot of very special conditions for life to be able to develop on a planet like Earth. This is a huge question, and because there are so many stars and planets, I think there probably is life out there. (From Alex at Paramount Elementary School in Meridian)

  2. If you could go into space forever, what would you find out there?

    We don't know how big the universe is. So, if you were to start traveling, nobody knows how far you could go. Humans have only been as far as the moon, and that was a long time ago. NASA is trying to figure out how to get humans beyond the moon, like an asteroid or even Mars. Kids in middle school are at a perfect age to start thinking about becoming an astronaut. One of you could be the first person to step foot on Mars! (From Jack at McDonnell Elementary School in Moscow)

  3. How many stars can you see at night?

    It depends on where you live. If you live in a city, the lights from the city can drown out a lot of the stars you would have been able to see. If you live in the country, there aren't as many city lights, and you can see many, many stars. (From Courtney at Saint Mary's Elementary School in Moscow)

  4. How many galaxies are out there?

    Astronomers don't know exactly how many galaxies there are. That's why we need kids like you to study astronomy, work for NASA and help figure out these questions. Astronomers do think there are about 100 billion other galaxies besides our Milky Way. (From Caleb who is homeschooled in Illinois)

  5. How do scientists take pictures of our galaxy?

    We actually can't do that. It would take way too long to get outside of the Milky Way to be able to take a picture of it. We've had to learn about it through other means, like studying the stars and how they are moving. That helps us learn about our own Milky Way. (From Iris at Cynthia Mann Elementary School in Boise)

  6. What would happen if two galaxies collided?

    Two galaxies colliding is a very common occurrence in the universe. You get a big galactic fireworks show when this occurs. One thing that occurs is that the galaxies lose their shape. If galaxies started out as disks or spiral galaxies, once they merge, they would typically become a ball shaped galaxy. Lots of crazy things happen when galaxies collide. (From Ethan at Cynthia Mann Elementary School in Boise)

  7. What is past our galaxies?

    Galaxies, in the past, were called Island Universes. They are mostly sitting out there in space. Bigger galaxies, like our Milky Way, have smaller galaxies orbiting around them. Just beyond our galaxy is mostly open space. Then much further away, there are bigger galaxies like ours. (From Sophie at Riverstone International School in Boise)

  8. How are galaxies made?

    A galaxy is a collection of stars. All the stars are made individually, and they are born out of clouds of gas and dust. The whole galaxy itself is born at different times within the universe. (From Ross at Cynthia Mann Elementary School in Boise)

  9. How many miles away is the farthest known galaxy?

    We measure very distant galaxies in terms of light years, or how far light can travel in a year. The most distant galaxies that we've discovered are over 13 billion light years away. NASA is building new telescopes, like the James Webb Space Telescope, to help us see early galaxies that we haven't been able to view yet. (From Michael at McDonald Elementary School in Moscow)

  10. How many planets are in our galaxy?

    We don't know. Great NASA missions have discovered many, many planets in our own galaxy. We now think that there are more planets than stars in the universe. How many? We don't know, but we know there are a lot! (From Annika at Whitman Elementary School in Lewiston)