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Space Day Q&A - The Universe, Galaxies & Solar System

How big is the universe?

No one really knows. We can not see the edges (if there are any). Scientists are working on the problem and so far the observed size of the universe is about 92 billion light years across.

galaxy  Tjefferson - Fotolia.com

How many galaxies are there in the universe?

No one knows the exact figure, but scientists make informed guesses based on how many visible galaxies there are in a small part of the universe, using equipment like the Hubble Space Telescope. In 1999 the HST estimated there were about 125 billion galaxies in the universe. Since then a German supercomputer has estimated about 500 billion.

What is a galaxy?

A galaxy is a massive collection of stars, dust and gas. A typical galaxy has hundreds of billions of stars. Astronomers estimate that our galaxy, the Milky Way, has between 200 and 400 billion stars.

What is the Milky Way?

It is the galaxy where our solar system is located.

What is the solar system?

The Solar System consists of the Sun and objects bound to it by gravity this includes the Earth.

What is a Galactic year?

Our galaxy is rotating. A Galactic year is the length of time it takes for the Solar System to go once all the way round the galaxy - about 225 million years. It is also known as a Cosmic year.

How many stars are there in our galaxy the Milky Way?

There are estimated to be between 200 and 400 billion stars in the Milky Way.

Can you see the Milky Way with the naked eye?

Yes, on a clear, moonless night, there will be an area of the sky with a band of stars which looks hazy.

Can you see any other galaxies with the naked eye?

Yes, on a clear, moonless night, you can see the Andromeda Galaxy which is about 2.5 million light years away.


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