The Milky Way and Andromeda galaxies are the two heavyweights in our cosmic neighbourhood. Our home galaxy reaches 100,000 light years across, around half the width of Andromeda, but both are now known to pack more mass than 200bn suns.

The white band of the Milky Way is visible on a clear night, but the Andromeda galaxy is more than 2m light years away and rarely seen by the naked eye. They are hurtling towards each other at a million miles an hour and could meet within fewer than 4 billion years - but it is highly unlikely that planets or stars from Andromeda will hit those in the Milky Way. The space between them is equivalent to a football field between grains of sand.

While the stars and planets will pass each other, clouds of dust and gas will smash into one another, creating enormous shockwaves that force particles together so violently they form new stars. The collision will create a new galaxy, which some astronomers have nicknamed Milkomeda.

It is hard to date galaxies, but the oldest star in the Milky Way is believed to be 13bn years old. The universe is thought to be 13.8bn years old.