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Explanation of the Universe in Astronomy - Succeed in Physical Science. Also refer to physics, space, light-year, Big Bang, theory, galaxies, stars, planets, Milky Way, Ron Kurtus, School for Champions. Copyright © Restrictions

Characteristics of the Universe

by Ron Kurtus (revised 26 February 2007)

The Universe consists of all the stars and galaxies of which we are aware. It is everything that is out there in the sky and is immense beyond imagination. In fact, it is difficult to grasp the great distances and large numbers involved in the universe. Our place and existence is tiny compared the everything else. The theory is that the Universe began with the Big Bang. There are also theories that other universes exist, parallel to ours.

Questions you may have include:

• How big is the Universe?
• How did the Universe begin?
• What are some other universes?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Useful tools: Metric-English Conversion | Scientific Calculator.

Note: If you want to hear the text being read, click the Play button. It takes a few seconds for the sound to start. The voices are somewhat mechanical for computer use.

Time = 3 min. 54 sec.

Size of Universe

The Universe is large in size and consists of billions of galaxies, which in turn consist of billions of stars.

Physical size

The size of the Universe is immense. It is estimated that the Universe is 156 billion (156,000,000,000) light years across. Since light travels at approximately 299,800 kilometers per second or 186,000 miles per second, you can see that the distance is very large.

(See Light-Year Calculations to make the calculations.)

Number of galaxies and stars

The Universe consists of approximately 100 billion galaxies. Each galaxy consists of anywhere from 10 million to 1 trillion (1,000,000,000,000) stars rotating around a center area.

Galaxy consisting of billions of stars

Each star in a galaxy is a sun, similar to our Sun. Some stars are much lager than our Sun, while others are smaller.

Our galaxy

Our Sun, the Earth and planets in our Solar System are part of the Milky Way galaxy. It is called that because, on a clear night, the many stars in our galaxy almost look like milk spread across the sky.

Our view of the rest of the Milky Way galaxy

Since we are in the Milky Way galaxy, our view of it is an edgewise view.

Beginning of the Universe

The major theory of how the Universe started is the "Big Bang" theory. This states that about 13.7 billion years ago (13,700,000,000 years) all matter was compressed to what some estimate was the size of a golf ball. It then exploded in a "big bang" and spread out until it has reached the enormous size of the present-day Universe.

While the matter was spreading out, it started to clump together into larger and larger masses. The turbulence of the explosion resulted in the spinning of the galaxies.

Measurements show that the Universe is still expanding. By interpolating the directions and velocities backward, astronomers have estimated the beginning time of the explosion. Of course, such measurements are highly inaccurate. There is debate on this theory and whether the Universe will continue to expand or will start to contract.

Other universes

There are theories that there may be other universes that we are not aware of. One theory says that there are parallel universes similar to our universe. Since we don't know how big our Universe is, there may be other universes outside our Universe's boundaries.

Another theory is that a black hole may actually be the starting point of the Big Bang of another universe. These are all abstract thoughts that cannot be proven.

(See Are Atoms Tiny Solar Systems? for another idea.)

Just the whole concepts of what's out "there" and where the universe exists are quite mysterious.

Summary

The universe is extremely large and consists of millions of galaxies and billions of stars. We are in the Milky Way galaxy. A major theory of the beginning of the universe is called the Big Bang Theory.

Answers to Readers' Questions

Help all those in your universe

Resources

The following resources provide information on this subject:

Websites

Astronomy Science @ NASA

Space Weather - News about Earth-Sun environment

Size of Universe - From Space.com

Astronomy Resources

Books

Top-rated books on the Universe

Miscellaneous

Mini-quiz to check your understanding

1. Why are light-years used to measure the size of galaxies?

2. Is there any proof that the Big Bang really happened?

3. How can there be other universes?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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Characteristics of the Universe