100th Anniversary of Astronomy’s Great Debate

Today’s NASA Astronomy Picture of the Day (APOD) is a celebration of the 100th anniversary of astronomy’s Great Debate held at New York’s Museum of Natural History between Harlow Shapley and Heber Curtis. Shapley argued that the Milky Way was the size of the known universe and that the Andromeda Nebula (M31) was part of it just like the Orion Nebula (M42). The debate ended with no decision either way. In fact Shapley’s model was accepted for years until Edwin Hubble and Henrietta Leavitt revolutionized the scale of the universe and proved that the Andromeda Nebula was in fact its own independent galaxy. 100 years ago today!

https://apod.nasa.gov/apod/ap200426.html
https://en.wikipedia.org/wiki/Great_Debate_(astronomy)
https://en.wikipedia.org/wiki/Edwin_Hubble
https://en.wikipedia.org/wiki/Henrietta_Swan_Leavitt
https://en.wikipedia.org/wiki/Harlow_Shapley
https://en.wikipedia.org/wiki/Heber_Doust_Curtis

What makes this anniversary relevant to the topic of Variable Stars is that it was Hubble’s discovery of a Cepheid type variable star in the Andromeda Galaxy. Coincident with this discovery, his associate Henrietta Leavitt had painstakingly measured Cepheid variables in the Milky Way and discovered Leavitt’s Law which relates the distance of a star with its period and apparent magnitude. With this knowledge Hubble and Leavitt proved Shapley’s model was incorrect.

Many of us associate the famed Hubble Space Telescope with spectacular visual images of the deep sky but in reality it is equipped with state-of-the-art photometers that continue the pioneering work of Edwin Hubble and Henrietta Leavitt. As a result Leavitt’s Law was modified to include adjustments for the effects of interstellar dust.