If you look outside on a clear and moonless night, the brightest stars you would see would be the planets Venus, Mars, Jupiter and Saturn.

Although it may seem like it, these stars are not fixed and only seem that way because they are near to us.

Our modern picture of the universe dates back to only 1924, when American astronomer Edwin Hubble demonstrated that our galaxy was not the only galaxy. There were many others, with tracts of the empty space between them.

He also figured out the apparent brightness of a star which depends on how much light it radiates and how far away it is from us. Hubble noted that certain types of stars always have the same luminosity when they are near enough for us to measure. He then discovered the distances to nine different galaxies.

Because of his contributions towards astronomy, we can now conclude that there are hundreds and thousands and millions of galaxies containing a hundred times the stars.

When you focus a telescope on one particular star in the galaxy, you will see that different stars have different colors. We can tell a star’s temperature from the color of light it gives off. We can determine which elements that are present in a star’s atmosphere by the colors missing from it.

In the 1920s, astronomers found that there were the same characteristic sets of missing colors for stars, but all shifted towards the “red” end of the spectrum. With this, Hubble discovered that the galaxies which had a red shift were not random, but nearly all were moving away from our galaxy, and the farther the a galaxy was, the faster it is moving away!

However, if the universe expanded at a certain rate, the force of gravity would cause it to stop expanding, and begin to contract. Alexander Friedmann, another scientist, made two theories that supported Hubble’s ideas.