¿ Astronomy Picture of the Day [1]Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2020 April 26 [2]See Explanation. Clicking on the picture will download the highest resolution version available. Edwin Hubble Discovers the Universe Image Credit & [3]Copyright: Courtesy [4]Carnegie Institution for Science Explanation: How big is our universe? This very question, [5]among others, was debated by two leading astronomers 100 years ago today in what has become known as [6]astronomy's Great Debate. Many astronomers then believed that our [7]Milky Way Galaxy was the entire universe. Many others, though, believed that our galaxy was just [8]one of many. In the [9]Great Debate, each argument was detailed, but no consensus was reached. The answer came over three years later with the detected variation of single spot in the [10]Andromeda Nebula, as shown on the [11]original glass discovery plate digitally reproduced here. When [12]Edwin Hubble compared images, he noticed that this [13]spot varied, and so wrote "VAR!" on the plate. The best explanation, Hubble knew, was that this spot was the [14]image of a variable star that was very far away. So M31 was really the [15]Andromeda Galaxy -- a galaxy possibly similar to our own. The [16]featured image may not be pretty, but the variable spot on it [17]opened a door through which humanity gazed knowingly, for the first time, into a [18]surprisingly vast cosmos. Centennial Celebration: [19]Astronomy's Great Debate was [20]100 Years Ago Today Tomorrow's picture: Another Great Debate? __________________________________________________________________ [21]< | [22]Archive | [23]Submissions | [24]Index | [25]Search | [26]Calendar | [27]RSS | [28]Education | [29]About APOD | [30]Discuss | [31]> __________________________________________________________________ Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell ([35]UMCP) NASA Official: Phillip Newman [36]Specific rights apply. [37]NASA Web Privacy Policy and Important Notices A service of: [38]ASD at [39]NASA / [40]GSFC & [41]Michigan Tech. U. References 1. https://apod.nasa.gov/apod/archivepix.html 2. https://apod.nasa.gov/apod/image/2004/HubbleVarOrig_Carnegie_2880.jpg 3. https://obs.carnegiescience.edu/PAST/m31var 4. https://obs.carnegiescience.edu/ 5. http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1995PASP%2E%2E107%2E1133T 6. https://apod.nasa.gov/diamond_jubilee/debate_1920.html 7. https://solarsystem.nasa.gov/resources/285/the-milky-way-galaxy/ 8. https://apod.nasa.gov/apod/ap020901.html 9. https://en.wikipedia.org/wiki/Great_Debate_(astronomy) 10. https://apod.nasa.gov/apod/ap170303.html 11. https://obs.carnegiescience.edu/PAST/m31var 12. https://en.wikipedia.org/wiki/Edwin_Hubble 13. https://apod.nasa.gov/apod/ap960406.html 14. https://hubblesite.org/contents/media/images/2011/15/2851-Image.html 15. https://apod.nasa.gov/apod/ap190909.html 16. https://obs.carnegiescience.edu/PAST/m31var 17. https://youtu.be/Fv4gWPurN9k?t=1582 18. https://apod.nasa.gov/apod/ap200405.html 19. https://apod.nasa.gov/debate/debate100th.html 20. https://phy.mtu.edu/debate/debate100th.html 21. https://apod.nasa.gov/apod/ap200425.html 22. https://apod.nasa.gov/apod/archivepix.html 23. https://apod.nasa.gov/apod/lib/apsubmit2015.html 24. https://apod.nasa.gov/apod/lib/aptree.html 25. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search 26. https://apod.nasa.gov/apod/calendar/allyears.html 27. https://apod.nasa.gov/apod.rss 28. https://apod.nasa.gov/apod/lib/edlinks.html 29. https://apod.nasa.gov/apod/lib/about_apod.html 30. http://asterisk.apod.com/discuss_apod.php?date=200426 31. https://apod.nasa.gov/apod/ap200427.html 32. http://www.phy.mtu.edu/faculty/Nemiroff.html 33. http://www.phy.mtu.edu/ 34. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html 35. http://www.astro.umd.edu/ 36. https://apod.nasa.gov/apod/lib/about_apod.html#srapply 37. https://www.nasa.gov/about/highlights/HP_Privacy.html 38. https://astrophysics.gsfc.nasa.gov/ 39. https://www.nasa.gov/ 40. https://www.nasa.gov/centers/goddard/ 41. http://www.mtu.edu/