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The Realm of the Nebulae (Silliman Milestones in Science)

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Edwin Hubble (1889 - 1953) summarized his research in his 1935 lectures on nebulae and also furthered discussion of the velocity-distance relationship for which he is known for, called Hubble's Law. He summarizes his landmark work of 1929 with the velocity-distance relationship via red-shifts that show that possibilities of actually being able to detect the "speed" of "nebulae", what we today call galaxies. He mentions how he showed that there are other galaxies like ours all over the universe and that the "nebulae" are actually galaxies. The red-shift velocity-distance data and relation is what Hubble is famous for and this information is what started making talks of the origins and expansion of the universe possible. Hubble himself, however, did not seem to make the link that the universe was expanding from his data, only that galaxies show a linear correlation in distances and velocities. Others had predicted that the universe was expanding such as Alexander Friedmann, Georges Lemaître (a Catholic Priest). In fact, Lemaître is said to have derived Hubble's Law but did not get a linear correlation. Hubble provided the linear relationship with his famous Hubble diagrams found in this book. For further research on the Big Bang, look at major players on the Big Bang Theory such as Ralph Alpher, Hans Bethe, George Gamow and their "Alpha-Beta-Gamma" paper on Big Bang nucleosynthesis, Fred Hoyle and his Steady-State Model of the universe, and a few others. A good book on the history of the Big Bang Theory is Big Bang: The Origin of the Universe (P.S.).

"The Realm of Nebulae" is Hubble's look at the history of astronomy from a bit of discussion on Ptolemy (the main geocentric view of the universe). Ptolemy's impact on modern cosmology is still seen today. His method of cataloging the stars that are found in Ptolemy's work Ptolemy's Almagest are still used today. Galileo critiqued Ptolemy in Dialogue Concerning the Two Chief World Systems (Modern Library Science), but Ptolemy still kicks butt today.

In these lectures, Edwin Hubble focuses mainly on "nebulae" which is the Greek word for "clouds" and discusses how these nebulae are actually galaxies with distant stars like our own, not astronomical clouds as it was believed at and before the time of Hubble by quite a few. Having this be the case, he attempts to acquire information such as velocity-distance relationships along with trying to determine the distribution of nebulae and their corresponding sizes such as the diameters of complete galaxies. The best part about this work is the utility and discussion of light spectra and luminosities of these stars to get the distances of stars. Light and luminosities of stars can give Doppler shift relationships that will tell if a given galaxy is approaching (Violet-shift, for example, since violet is at a higher frequency in the light spectra) or expanding (red-shift, for example, since red has lower frequency in the light spectra). Hubble focused on the red-shifts, via spectrograms, since that is what he was able to detect and gave him what he was looking for. He makes plots or maps of clusters of nebulae to get a better visual of nebular distribution in the heavens.

The main thing to get from his lectures in the book is his assumptions and derivations that he uses in making the Doppler red-shift velocity-relationship which essentially constitutes Hubble's Law. Also, as mentioned earlier, his famous Hubble diagrams can be found here too along with his summary of his landmark 1929 paper. There are pictures of clusters in here too. It should be an interesting read for anyone interested in the methods of finding the distances and velocities of expanstion that galaxies display.

How do we know how far a galaxy is? Hubble will tell you in these lectures. Also these lectures help give background lay a foundation for the origins of the universe and the expansion of the universe research.

Here are the Chapter titles for those who are curious:

1. The Exploration of Space
2. Family Traits of Nebulae
3. The Distribution of Nebulae
4. Distances of Nebulae
5. The Velocity-Distance Relation
6. The Local Group
7. The General Field
8. The Realm of Nebulae

Though Hubble did not make the link between his data and the expansion of the universe, Hubble's discovery of the red-shifts helped in basically putting the eternal universe (a universe that always existed and had no origin), of the previous natural philosophers, to rest.

And cosmology would never be the same again.

This book was amazing! It helped us so much with a project! WOOT!