A future collision billions of years in the making

Although the universe is expanding, collisions happen all over. Planets collide, stars collide, meteors and comets hit planets, etc. However, sometimes larger "collisions" occur where no objects actually hit each other, but it's more of a merger. This can occur between galaxies and we have observed it occurring in different parts of the universe. Our galaxy, the Milky Way, is currently on a collision course with another galaxy called Andromeda. We know this because of the method of measurement used to determine how far away galaxies are from us. Edwin Hubble and other scientists in the 1920's, using the Doppler-shift method, observed many of these galaxies moving away from us at very quick speeds. They were able to deduce from this that the universe is expanding. This also became known as Hubble's law. However, Andromeda looked different in the observation.

Using this method of measurement, it was discovered that Andromeda is headed right for our galaxy. This collision, or merger, will not occur for another four billion years. However, if the earth is still here, it will drastically change what our night sky looks like.

It is unlikely that the stars in each galaxy will collide as they are very spaced out since these are two massive galaxies. I wish I could be here to see it because a night sky like that would be even more incredible than what ours looks like now!