For a long while astronomers believed that all the stars in the universe were contained inside the Milky Way Galaxy. But when Edwin Hubble turned his eyes heavenward in the 1920s – with help from a very powerful telescope – he proved that what were previously thought of as mere nebulae were actually other galaxies. And there are lots of them out there. Around 170 billion of them spin through the observable universe, so perhaps it’s not surprising that our own home galaxy is due to collide with its nearest neighbor, the Andromeda Galaxy. But, there’s no need to put on your crash helmet just yet. At the rate we’re speeding toward each other – around 70 to 80 miles per second – it’s going to take a while for the smash-up: about 3 to 4 billion years.