There are two possibilities. Either the spiral character of M51 was indeed noticed as soon as the galaxy was first examined with the 6—foot reflector Rosse , or it was not. This suggests that both Robinson and South may have seen spirality in M51, together with Rosse, possibly as early as 5 March However, with their attention focused on the resolvability of the nebula, it is conceivable that none of the three would have found the spiral arrangement worthy of note.
It is also possible that they did not recognize the spiral structure simply because they were not looking for it. As Chapman pers. The approach of astronomers to the problem of the nebulae changed dramatically, however, in June It was then that the Third Earl's drawing of M51, made in April that year, was circulated at the Cambridge meeting of the British Association for the Advancement of Science, evidently to much acclaim Herschel Very soon after, the spiral form of arrangement was detected; and our attention was then directed to the form of nebulae, the question of resolvability being a secondary object.
It seems likely that Rosse, Robinson and South could have seen the spiral arrangement of M51 when it was first observed, probably on 5 March , though there is no evidence that they noticed it. Be this as it may, spirality had certainly been detected by the end of April Hoskin , Rosse , the month in which Rosse drew the spiral arrangement of M For comparison, figure 2 shows the copy of Rosse's original sketch which was commissioned and published as a double—plate by Nichol Taken from Nichol plate VI.
Taken from Parsons figures 1 and 2 facing p No—one doubted the reality of the reported spiral structure of these nebulae, but it seems not to have been until around 11 March i.
It would be interesting to examine the surviving correspondence of Rosse, Robinson, Nichol and others from around March , and perhaps other sources, to determine whether further light can be shed on the first observation of spiral structure. Google Scholar. We were about to be knocked off our egotistical little pedestal once again. Edwin Hubble was born in Missouri in and moved to Chicago in In high school, he broke the state record in the high jump, and went on to play basketball for the University of Chicago.
He won a Rhodes scholarship and studied law at Oxford. He earned a Ph. After serving in World War I and rising to the rank of major, he got bored with law and returned to astronomy.
However, because star formation requires relatively dense clouds of gas, which are only found in galaxies, the vast majority of stars are found in galaxies. Until about years ago, the Milky Way galaxy was thought to be only a few thousand light years across, and most thought it was the entire universe. Other galaxies had been discovered, but they were thought to be smaller objects within our galaxy. The first galaxies were identified in the 17th Century by the French astronomer Charles Messier , although at the time he did not know what they were.
Messier, who was a keen observer of comets, spotted a number of other fuzzy objects in the sky which he knew were not comets. If you remember our discussion of Cepheid stars, they have a very specific relationship between their variability period and their luminosity.
Thus, if you measure the period of a Cepheid variable, you can estimate its luminosity. Then, if you measure the apparent brightness of the Cepheid which you can do using the same observations you took to get its period , you can measure its distance. The discovery of the first variable star in M31 was one of many discoveries by Edwin Hubble that fundamentally revised our understanding of the Universe. You can learn a bit more about this discovery at the following websites:. We will learn more of Hubble's accomplishments later in this lesson and in the next lesson, but if you would like to read more about the man who is widely considered the greatest astronomer of the modern age, you can consult the following:.
The discovery that the spiral nebulae are other galaxies similar to the Milky Way again caused a large shift in our understanding of the Universe and our place in it.
For example, prior to Hubble's discovery, Shapley believed that the Universe was filled almost entirely by the Milky Way. Hubble showed that, in reality, the Milky Way is just one object in a universe filled with many billions of other similar objects, which forces us to realize that the universe is much larger than the Milky Way.
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