A good history of astronomy from the late 19th century to the 1930s that discusses the discovery of the true significance of spiral nebulae, the size of the universe and its expansion. Other advances during this time, e.g. the nature and classification of stars, are mostly not discussed. Many later misconceptions about who did what are debunked, and there is fascinating discussion of the people involved with no attempt to gloss over their often too human characteristics. ( )

This book is a fantastic, popular-science history of a pivotal era in astronomy: the moment in time when we went from a belief that the Milky Way was the Universe entire, to the knowledge that the Milky Way is but one galaxy in a Universe comprising billions of others.

Both the famous names (Hubble, Einstein, etc) and the less well-known players (Vesto Slipher, Milton Humason, Georges Lemaître, etc) are represented in this fascinating, well-written, and well-researched book. ( )

Lots of history on astronomy i did not know. Colorful characters. Very interesting how all this was done before computers ( )

It is difficult to believe, in this day and age, with the Hubble Space Telescope and other enormous telescopes regularly providing us with stunning views of the Universe, that astronomy in the early twentieth century more closely resembled the studies of the Renaissance than modern space studies. Little was understood about the Universe beyond the Milky Way and, in fact, the most commonly held belief was that the Milky Way was the Universe, in its entirety. Marcia Bartusiak’s “The Day We Found the Universe” chronicles the work of the men, and in some cases women, who laid the groundwork for the study of modern astronomy and who discovered how small and insignificant our galaxy, star, and planet truly are in this great Universe.

The first half of Bartusiak’s work is dedicated to the battle over the nature of galaxies, what were then termed “nebula” and which appeared in telescopes as a hazy collection of “shining fluid.” Some astronomers believed them to be accumulations of dust or gas within the Milky Way, while others argued that they were, in fact, island universes, much like our own galaxy and situated at substantial distances away from us. As telescopes improved, these nebulas gained greater definition and the battle ultimately culminated in the Great Debate, conducted in April 1920 before the members of the National Academy of Sciences. On one side of the debate was Harlow Shapley of the Mount Wilson Observatory, the man who first discovered that the Milky Way galaxy was far larger than originally believed and that the Sun was not at its center. He argued that the Milky Way was the entirety of the Universe and that the “spiral nebula” as they were then called (the last quarter century of telescopic development had allowed for greater clarity of galaxies) were merely collections of gas within our own galaxy. He also argued that Adriaan Van Maanen’s discovery of rotation within the nebulae rendered it impossible for them to be situated very far from our own galaxy as the relative speeds required then would have them rotating faster than the speed of light.

On the other side of the debate was Heber Curtis of the Lick Observatory, who argued that the light spectrum emanating from the nebulae matched that of collections of stars, rather than accumulations of gas. He also argued that the Milky Way was one-tenth the size Shapley believed which allowed him to partially reconcile the “island universe” hypothesis with Van Maanen’s ultimately disproven observations.

The Great Debate actually decided little since the two scientists were mostly speaking past each other. In fact, they both ended up being partially right and partially wrong. What the Great Debate did do was focus the work of another astronomer at Mount Wilson: Edwin Hubble.

The second half of “The Day We Found the Universe” follows Hubble’s work at Mount Wilson’s Hooker Telescope, then the largest telescope in the world. Hubble was the first to discover Cepheid variable stars in the spiral nebulae. These variable stars (whose size and luminosity change with regularity) were proven to be useful in calculating stellar distance by Henrietta Swan Leavitt fifteen years earlier. Using these standard candles, Hubble proved that these spiral nebulae were actually “island universes” far beyond the reaches of the Milky Way galaxy. Hubble’s work then went to figuring out how these galaxies moved and he was able to prove that galaxies were moving away from us and how quickly they were doing so. This discovery would ultimately inform the discussion of the nature and creation of the Universe in the following decades.

Bartusiak writes with vigor and makes a potentially dry subject come to life. Some of the discussion gets a bit academic and may be difficult to follow for readers without at least a little understanding of astronomy but, for the most part “The Day We Found the Universe” is a wonderful and readable book, capable of sparking interest in astronomy in any reader. ( )

A very interesting book. I have to admit that when I first started to read it, I found the writing very dry, and only my interest in the subject kept me reading. I'm not sure whether the writing improved throughout the book, or if I became used to her writing style, but by the end I loved the book. I hope she writes a continuation covering the discovery of the Big Bang theory, and the astronomers involved in that discovery.

The author starts off talking about each astronomer and their discoveries (Keeler, Curtis, Hale, etc), leading up to Hubble finding that the spiral nebulae were actually other galaxies. Around the halfway point of the book the astronomers tales become intertwined, and this is where I found the book to be the most interesting. I would definately recommend this book, as it sheds light on some lesser known astronomers who had a big hand in leading up to Hubble's discoveries. ( )