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How many galaxies are there and will NASA ever explore them all?

Asked by: Alex Madison
School: Maine Endwell Middle School
Grade: 6
Teacher: Kevin Wagstaff
Hobbies/Interests: Sports, running, football and basketball
Career Interest: Football player

Answer from Andrew Telesca, Jr.

Adjunct lecturer in physics, Binghamton University

Your question is one that has been asked by many people over many years. The simple answer is that some studies or counts of galaxies have shown that there are at least 100 billion galaxies in our Universe. Other counts indicate there may be as many as 500 billion galaxies in our Universe. Why is there such a difference in the results of the counts?


The differences in the numbers are due to how the counts are done, and also improvements in the instruments that the astronomers used to make the counts. For example, when you look at the night sky with just your eyes on a clear night you see quite a few stars. If you look at the same sky through a pair of binoculars you see many more stars in a smaller region of the sky. This is the way it is for astronomers.  Many years ago the telescopes that astronomers used were not nearly as large as the telescopes in use today. When astronomers looked at the sky through their telescopes many years ago and tried to count the galaxies in the sky, they counted fewer galaxies than we can count today.


 Modern day astronomers have different tools to use to count galaxies. We have very large ground based telescopes and we also have telescopes, like the Hubble space telescope, in orbit around the earth. Each of these tools provides slightly different information about the numbers of galaxies.


A few years ago the Hubble space telescope took a picture of a very small part of the sky. This part of the sky was about 1/150 the size (area) of the full moon. Through this small area of the sky Hubble could see as far as is possible for us to see in the Universe. Scientists counted the number of individual galaxies in this area of the sky and came up with a number of 3000. If the Hubble were to do this for every same size region of the sky, the total count of galaxies would be over 100 billion. But, these would be the galaxies that can be seen by the Hubble. Newer and better space telescopes could count a larger number of galaxies because, just like looking through binoculars, the newer space telescopes could see more. Another count, done in a different way, shows almost 500 billion galaxies in the Universe.


The second part of your question can have two answers. The first answer is that since most of the space telescopes are, at least in part, NASA projects, NASA is already exploring the galaxies. If you mean, will NASA be sending spacecraft to other galaxies, this is a question that can only be answered by someone in the distant future. The problem is that it takes a long time for spacecraft using current technology to travel long distances in space.


For example, one of the first planetary spacecraft, called Pioneer, recently sent its last signal back to earth. It was launched in 1972 and has been traveling for over 30 years. When it stopped transmitting it was about 7.6 billion miles from earth. This is about 80 times the distance from the Earth to the Sun.


Our galaxy, the Milky Way, is about 80,000 to 100,000 light years in size, and a light year is about six trillion miles. It would take Pioneer about 3.1 billion years just to leave our galaxy. The time to travel to a nearby galaxy, about 167,000 light years away, would be even greater than the time to reach the edge of the Milky Way.  Other galaxies are millions and billions of light years away.


So, traveling to other galaxies will depend on some breakthroughs in space travel that are presently in people’s imaginations or daydreams today. It will be up to you and people like you to keep asking the questions and then learn enough in school to try to answer the questions. You may be the one to discover the breakthroughs that will let us explore the galaxies.

Last Updated: 3/1/17