Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.
Niels Bohr
Less than one hundred years ago, as far as most anyone knew, we lived in a lonely universe. This was a time when the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy.Wiki
Needless to say, no one then could have imagined the Universe as it is known today.
In 1923, however, someone changed everything...
The young veteran, a Major in the World War, arrived in Pasadena not long after the Hooker Telescope. The atheletic high school physics teacher and basketball coach had completed his PhD in Astronomy at the University of Chicago‘s Yerkes Observatory, undoubtably coming to the attention of superstar astronomer George Ellery Hale who offered him a staff position at Mount Wilson Observatory. It was an incredible opportunity for the 29 year old Rhodes scholar to continue his study of gaseous nebulae—the very subject of his doctoral thesis (Photographic Investigations of Faint Nebulae)—at the world‘s newest and largest telescope.
The study of nebulae is essentially a photographic problem for cameras of wide angle and reflectors of large focal ratio. The photographic plate presents a definite and permanent record beside which visual observations lose most of their significance. Perhaps the one field left for the older method is the measurement of sharp nuclei deeply enshrouded in nebulosity. New nebulae are now but rarely seen in the sky, although an hour's exposure made at random with a large reflector has more than an even chance of adding several small faint objects to the rapidly growing list of those already known. About 17,000 have already been catalogued, and the estimates of those within reach of existing instruments, based on the ratio of those previously known to those new in various fields, lie around 150,000.1
Edwin Hubble likely had no idea on that first day in 1919 as he stood under the giant telescope the impact his work would have on how we view ourselves, the Earth, and the universe.
Take an Incredible Spherical Panoramic Tour of the Hooker Telescope
prepared for the Observatory by Carel Struycken, Star Trek's Mr. Homn and the Adams Family member Lurch. Click here to load the tour. It will take you to 20 different spots on the mountain, including spaces not open to visitors. Use the built-in navigation bar to select your vantage point, zoom in and out, switch to full screen, and turn auto-rotation on/off. Then click and drag your cursor go left-right and up-down. There is no direction in which you cannot look! If you are comfortable navigating without the continuous showing of the bar, click here. You can retrieve the nav bar by moving your cursor to the bottom of the screen. For more about Mr. Struycken's amazing spherical panoramas, click here.
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His immediate future, however, consisted of long nights preparing and loading photographic plates and even longer days measuring and plotting and cataloging his results. Just four years later he would be on the verge of a major discovery, one that would answer an ongoing Great Debate. At that time, there was no consensus on the size of the Milky Way let alone the universe,
many astronomers thought spiral nebulae, such as Andromeda, were part of our Milky Way galaxy. Others weren't so sure. In fact, astronomers Shapley and Heber Curtis held a public debate in 1920 over the nature of these nebulae. During the debate, Shapley championed his measurement of 300,000 light-years for the size of the Milky Way. Though Shapley overestimated its size, he was correct in asserting that the Milky Way was much larger than the commonly accepted dimensions. He also argued that spiral nebulae were much smaller than the giant Milky Way and therefore must be part of our galaxy. But Curtis disagreed. He thought the Milky Way was smaller than Shapley claimed, leaving room for other island universes beyond our galaxy.hubblesite
In 1923 Hubble began a survey of the Andromeda nebula with the 100-inch Hooker Telescope a huge target for the world's largest telescope. He spent several months photographing the entire nebula using many dozens of photographic glass plates in order to cover the entire nebula. Then, he turned his attention to 3 specific regions.
One of them was deep inside a spiral arm. On the night of Oct. 5, 1923, Hubble began an observing run that lasted until the early hours of Oct. 6. Under poor viewing conditions, the astronomer made a 45-minute exposure that yielded three suspected novae, a class of exploding star. He wrote the letter "N," for nova, next to each of the three objects.hubblesite
When Hubble went back and compared the October 5th and 6th plates against those taken earlier he found that one of the star‘s intensity varied over a much shorter period of time than a typical novae. He realized, then, that the star was a type called a Cepheid variable. He continued his observations over the next few months, plotting its light curve and determining its period of 31.4 days. This was the first of some 36 variable stars (twelve of them Cepheids) Hubble found in Andromeda, so it was imaginatively named V1 :).
Cepheid variable stars are important astronomical objects. This class of stars can be used them as standard candles. That is, their intrinsic luminosity is well understood via a log linear relationship (period-luminosity) so astronomers are able to use that relationship to estimate the distance from Earth for objects beyond the sensitivity of parallax. This method was pioneered by Henrietta Swan Leavitt.
Although she was not able to tease out all of the implications of her discovery, others, such as Harlow Shapely and Ejnar Hertzsprung did use her data to measure the size of the Milky Way (Shapely) and distance to several nearby stars (Hertzsprung). Her paper seminal paper is here, if you‘re interested 1777 Variables in The Magellanic Clouds published in 1908. Here is her paper, published in 1912 describing the period-luminosity relationship. Gösta Mittag-Leffler, of the Swedish Academy of Sciences, was so impressed by her work that he wanted to nominate Ms. Leavitt for a Nobel Prize, unfortunately she had passed away.
Essentially, Leavitt's idea was that if you know the intrinsic brightness of a source is then you can deduce its distance by it‘s apparent brightness. This Khan Academy video describes Cepheids and the method of estimating the distance in greater detail.
With this techique in hand Edwin Hubble was able to estimate the distance to the Andromeda nebula.
Hubble obtained enough observations of V1 to plot its light curve, determining a period of 31.4 days, indicating the object was a Cepheid variable. The period yielded the star's intrinsic brightness, which Hubble then used to calculate its distance. The star turned out to be 1 million light-years from Earth, more than three times Shapley's calculated diameter of the Milky Way.
After gathering his data Hubble sent Harlow Shapley (mentioned above) a letter describing his results. After receiving the missive, Shapely, convinced by the data, is reported to have said, "Here is the letter that destroyed my universe." Shapely and fellow astronomer Henry Norris Russell persuaded Hubble to submit a paper for the joint meeting of the American Astronomical Society and American Association for the Advancement of Science at the end of 1924. The paper Extragalactic Nature of Spiral Nebulae, delivered in absentia, shared first prize for best paper. It was the paper that changed forever our little island universe.
So there you have the story about the big bang in human knowledge of the universe. Overnight, it seems, we went from a single galaxy to millions upon millions of them.
Links
Edwin Hubble
Mount Wilson Observatory
Mount Wilson Observatory
Mount Wilson Observatory
Carel Struycken
Spherical Panoramas and giga-pixel images, California, Los Angeles, Pasadena, Hollywood, Carel Struycken
HubbleSite - NewsCenter - Hubble Views the Star that Changed the Universe (05/23/2011) - The Full Story
The Great Debate
Parallax
Henrietta Swan Leavitt
A Science Odyssey: People and Discoveries: Henrietta Leavitt
Harlow Shapley
Ejnar Hertzsprung
Gösta Mittag-Leffler
Cepheid variable
Harlow Shapley
Henry Norris Russell
Periods of 25 Variable Stars in the Small Magellanic Cloud
1777 variables in the Magellanic Clouds
Henrietta Swan Leavitt, with Plate XVII
Hubble's Announcement of Cepheids in Spiral Nebulae
Cepheids in spiral nebulae
Extragalactic nebulae
I hope I‘ve entertained and informed you with this little diary. I look forward to your comments and critiques below. Thank you for taking the time.
palantir