Hi, I am a 9th grade student in NY. We are learning about stars and galaxies in Science class now and I have a question. Today in class we watched a segment of a movie about our Milky Way. In the film, there was a scientist and he was talking about our galaxy and all the others. In his discussion he said that we cannot leave our galaxy, then he sad that there were many other galaxies in the universe. My question is, how can we know that there are other galaxies if we cannot leave ours? Thank you for your time.
The reason that we cannot leave our galaxy is that it is so huge that the fastest space ships we could build at the moment could not get out of it in a reasonable amount of time. Maybe at some point far in the future we may develop technologies so that we can leave the galaxy, but that's a long long way off.
Although we cannot visit the other galaxies we can see that they are there through telescopes—that's how we know they exist. It was very hard to discover how far away they were and took the best minds in Astronomy many years to settle the issue. There was a famous debate in the 1920s over the nature of the "spiral nebula" (the early name for galaxies). An astronomer called Shapely took the position that they were in our galaxy, while another astronomer called Curtis argued that they were outside it. Curtis's arguments won in the end, and the vast distances to other galaxies and the even larger size of the Universe only came to light after that!
This page was last updated June 27, 2015.