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Hubble Discovers the Universe!

Nearly a century ago, on the night of October 6, 1923, Carnegie astronomer Edwin P. Hubble took a plate of the Andromeda Galaxy (Messier 31 or M31) with the Hooker 100-inch telescope of the Mount Wilson Observatory.  This plate, with identification number H335H ("Hooker plate 335 by Hubble"), is famous for having led to his discovery of the first Cepheid variable star in M31, which established beyond any doubt that M31 was a separate galaxy from our own. In other words, that night Hubble simply discovered our Universe!

This is the famous Plate No: H335H of a Variable star taken by Hubble and Humason from Mount Wilson observatory that proved the existence of other galaxies outside of Milkyway. Till then Universe was thought to be just our galaxy. An iconic picture in the same league as Earthrise and Pale Blue Dot pictures.

Picture credit: Copyright © 2020 Carnegie Science

Until that historic night, scientific community was divided over the true limits of our Universe. Popular belief was that our Universe was confined to our home galaxy the Milky Way. Many others, though, believed that our galaxy was just one of many.

Few years before that, On April 26, 1920, exactly 100 years ago at the time of writing this article, the energetic and ambitious scientist Harlow Shapley and the concise and clear-headed astronomy professor Heber Curtis came head-to-head in what is now known as the Great Debate. In the 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 Andromeda Nebula, as shown on the original glass discovery plate digitally reproduced here. When Edwin Hubble compared images, he noticed that this spot varied, and so wrote "VAR!" on the plate. The best explanation, Hubble knew, was that this spot was the image of a variable star that was very far away. So M31 was really the Andromeda Galaxy -- a galaxy possibly similar to our own. The featured image may not be pretty, but the variable spot on it opened a door through which humanity gazed knowingly, for the first time, into a surprisingly vast cosmos.

This image is as iconic as the image of the Earth rise taken from the Moon or the image of Earth as a pale blue dot taken by Voyager 1 while flying past Saturn. More importantly, it also helped to diminish our egos further as we realised that our place in the Universe is nothing significant to write home about. Our planet is just a tiny drop in the vast cosmic ocean and we the mortals on it pales into near non-existence.

The unsung hero in this discovery is the American astronomer Henrietta Swan Leavitt, who had earlier devised a new approach at that time to measure distance to far away celestial entities using variable stars, or Cepheid Variables, to be precise. More on that in a later blog.

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