Mount Wilson Astronomer Estimates Milky Way Ten Times Bigger Than Thought

The primary message of this article is that at the beginning of the 1900s, astronomers believed that the Milky Way galaxy comprised the entire Universe. A secondary message is that astronomers must use indirect methods to determine distances in the Universe.

In 1919, astronomers did not realize that there were galaxies in the Universe besides our own Milky Way. That discovery did not happen until 1924. At the time, they thought that stars and nebulae populated the Universe uniformly. Astronomers had observed nebulae, some of which appeared spiral, but they could not resolve these nebulae into stars. There was a debate going on at the time of this issue of the Cosmic Times, as to whether these nebulae were indeed just gas and dust or if they were comprised of stars. The telescopes of the time were not sensitive enough to settle the question.

We now know that some of the nebulae were, indeed, separate galaxies and there are great distances between the Milky Way and these distant "nebula". However, some of the nebulae are bound clouds of gas and dust residing in our Milky Way. This question, and its resolution, will be discussed further in the 1929 issue of the Cosmic Times.

This article also contains the first mention in the Cosmic Times of Henrietta Leavitt and Cepheid Stars. These stars become more important in the 1929 and 1955 issues of the Cosmic Times. The 1929 issue discusses Leavitt's observations and their importance in more detail. Cepheid stars are variable stars that are seen to brighten and dim with a regular period. Leavitt saw that the period of the variation was related to the average brightness of these stars. The stars with the shortest period were dimmer and the longest period stars were brighter. Leavitt was observing stars in the Small Magellanic Cloud, so they could all be considered to be at the same distance. This meant that they could be used as distance indicators, if only a few Cepheids could be found with a known distance. Shapely was attempting to calibrate this Cepheid period-luminosity distance scale.