2020 April 30 - Andromeda Island Universe
Channel: APOD Podcast
Date: 2020-04-30

In today's image, we see the Andromeda Galaxy. This galaxy and other "spiral nebulae" were the subject of a great debate a hundred years ago. The questions was if these objects were part of our Milky Way or if they were island universes (galaxies) of their own. The debate was not resolved for several years until Edwin Hubble detected Cepheid variable stars in the Andromeda Galaxy and was able to determine its distance - demonstrating that it could not be a part of your Milky Way.

This YouTube channel is an authorized New Media Mirror Site for APOD. You can access the image and website directly at: https://apod.nasa.gov/apod/ap200430.html.