Islands of Stars

Milky Way Galaxy

Until 1924,  the Milky Way galaxy - our galaxy - represented the entirety of the universe. That year, astronomer Edwin Hubble announced the discovery of other galaxies.

Hubble was studying the Andromeda Nebula at Mount Wilson observatory in California, — the most powerful telescope in the world at that time. He was able to to distinguish individual stars within the nebula.

One of the stars he observed is called a Cepheid variable. This is a type of star that pulsates and is very bright and that by observing and measuring its brightness and the length of time it takes to go from bright to dim and back again, one could calculate the star’s distance from the Earth. 

Hubble calculated that the star he was observing was 800 thousand light-years away, more than eight times the distance of the farthest star in the Milky Way, and so he realized that the “cloud of gas” he’d been observing was really another vast galaxy that was very far away. He renamed the Andromeda Nebula the Andromeda Galaxy.

Hubble would discover 23 more separate galaxies. Our Milky Way galaxy is just one of many little islands of stars.

Andromeda Galaxy