On this day in 1920
On the 26 April 1920 a debate took place between two American astronomers, Heber Curtis and Harlow Shapley. Curtis argued that fuzzy patches in the night sky called ’spiral nabulae’ are separate galaxies or ‘island universes’, lying far away from us. Curtis claimed that our own galaxy was less than 30,000 lightyears wide, with the Sun located near the centre. Shapley agued that the spiral nebulae were merely nearby gas clouds inside the Milky Way. He also claimed the Universe was composed of only one big galaxy more than 300,000 lightyears wide, with the Sun lying far away from the galactic centre.
The debate was resolved in the mid 1920’s by Edwin Hubbles work which involved pinpointing Cephid Variables in M31 (a spiral nebula). His work showed that the distance to M31 is much greater than Shapley had imagined as M31 is indeed an ‘island universe’ now better known as the Andromeda Galaxy.
It’s now known that Curtis was right about other galaxies existing, whilst Shapley’s idea about the location of the Sun was better. Both astronomers were wrong about the size of the Milky Way. Astronomers current predictions have our galaxy at approx 100,000 lightyears wide.
