You will probably have heard of the Hubble Space Telescope. It has orbited our planet 333 miles up since 1990 and has spectacularly opened up our view of the Universe with many beautiful images and discoveries. It was named after the American astronomer Edwin Hubble. He fought in the Great War and when he returned in 1919, Hubble joined the Mount Wilson Observatory with its 100-inch mirror Hooker Telescope that was the most powerful on Earth at the time. Hubble soon met his scientific rival, Harlow Shapley, who was known for measuring the size of our own galaxy, the Milky Way. Like most astronomers of the time, Shapley thought that the Milky Way was the whole Universe. Strange objects called nebulae (meaning “clouds”) were observed and were thought to be relatively nearby patches of dust and gas within the Milky Way. 

Then in October 1923, Hubble spotted what he first thought was a “nova” (a star that rapidly brightens) in the “nebula” in the constellation of Andromeda. After scrutinizing previous photographic plates of the same area, he realised that it was a Cepheid variable star, a particular sort of star that could be used to accurately measure distance. Hubble realised this meant that the Andromeda nebula was at least a million light-years away and so was outside the Milky Way and was in fact a galaxy in its own right, containing billions of stars. This is the Andromeda Galaxy. 

So, if you look up to view the stars on a clear night you should see a big “W”made up of five stars in the constellation Cassiopeia. If you look down from the second “V” in the “W” you may notice a bright smudge.

This is the whirlpool-like Andromeda Galaxy that looks like our own home galaxy, the Milky Way, but contains an estimated 1 trillion stars; that’s 1,000,000,000,000,000,000 stars!!!. This is vastly more stars than are estimated to exist in our Galaxy which only (only!) contains about 250 billion (250,000,000,000) stars. The Andromeda Galaxy is so huge that it takes light about 200,000 years to travel across its diameter which is twice that of our Milky Way. It may be bigger but at 10 billion years old is younger than our 13.2 billion year old galaxy. This monster is over 2.5 million light years away but gravity is pulling us together at 37 miles per second on a collision course…BRACE FOR IMPACT!!! 

The image above shows what it will probably look like over billions of years of a VERY slow-motion merger. It won’t happen for another 4.5 billion years and because the space between stars in each galaxy is so massive its unlikely that any will actually collide.

As it says on the cover of Douglas Adams’ The Hitchhikers Guide to the Galaxy; “DONT PANIC!”

Glynn Bennallick