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发表于 2010-8-25 22:37:39
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2010-08-16
Edwin Hubble, the man behind HST
作者：Boris Häußler
Who is Edwin Hubble, the guy who gave the Hubble Space Telescope its name? Who is the mysterious guy behind the telescope?
Edwin Hubble
Well, actually, Edwin Powell Hubble is not the ‘man behind the telescope’ at all. He was born on 20th of November 1889 in the US and studied Physics and Astronomy in Chicago. He then, interestingly, went to Oxford, UK (now, of course, one of the main departments participating in Galaxy Zoo), to study Jurisprudence, later Spanish. Given that he was also very sporty (he won several state track competitions and set the state’s high school high jump record in Illinois), I think it is fair to call Hubble a person with multiple talents. In England, he also picked up some English habits and his dress code, some to the annoyance of his american colleagues in later years. I don’t know many pictures of him, the one on the right is possibly the most famous (usually used in scientific talks at least). Smoking his pipe on his desk, he really looks like an English gentlemen of his time (Well, maybe he’s lacking a hat).
Edwin Hubble died on September 28th 1953 in California (his houseis now a National Historic Landmark at thislocation), long before the real planning for the HST had begun. Earlier ideas did exist, since 1923, after it was explained how a telescope could be propelled into Earth orbit and in 1946, Lyman Spitzer (who interestingly enough has his own space telescope named after himself now) had already discussed the advantages (which I will discuss in the next post about the planning of the HST) of an extraterrestrial observatory, but it took until 1962 for the US NAS (not NASA!) to recommend the development of a space telescope for other purposes than observing the sun (two orbiting solar telescopes were in fact already active at that time). In 1965, 12 years after Hubbles death, Spitzer was appointed head of the committee to define the scientific objectives for this new telescope, so really, he is the ‘man behind the Hubble Space Telescope’.
So why is the telescope named after Edwin Hubble then?
After some years of teaching at the university back in the US and after serving in WWI as a major, he returned to the Yerkes Observatory at the University of Chicago, where he finished his Ph.D. in 1917. The topic of his thesis was ‘Photographic Investigations of Faint Nebulae‘ (it only consists of 17 pages, a fact that possibly makes every PhD student cry nowadays). At that time, these nebulae were still considered to be part of the Milky Way, something that was waiting for a real genius and careful observer to be revealed as a mistake.
The Hooker Telescope
In 1919, Hubble took on a staff position in California at the Mount Wilson Observatory near Pasadena where he stayed until his death in 1953. Just 2 years previously, a new telescope had been finished at the site, the Hooker telescope (the slightly unfortunate name comes from John D. Hooker who funded the project), a 100-inch Reflector telescope, which today is still there and, after some recent upgrades and modifications (although preserving the historical origin wherever possible), is again used for scientific purposes. With its ‘adaptive optics’ system (see next post) its resolution today is 0.05 arcsec, the same as resolution of the HST. From 1917 to 1948, the Hooker telescope was the world’s largest telescope.
Hubble used this new, state-of-the-art telescope to continue the work on nebulae that he had started in Chicago by identifying Cepheid variable stars in them. Cepheids have the very convenient characteristic, that the period of their variability is a simple function of their brightness. So by measuring their period, astronomers can immediately tell how bright these objects are in a standard system. Measuring their apparent brightness allows to measure their actual distance. By doing this, Hubble noticed that they are far too distant to be part of our own galaxy, but instead are extragalactic systems, islands of stars (and possibly life) in the vast nothingness of space. Other distant ‘Milkyways’, just like our own.
We now call them ‘galaxies’.
Being some of the closest galaxies to our own, most of the objects that he worked on are now very famous, some also through images by the HST. The most famous of all is possibly M31, the closest big galaxy to our own, the Andromeda galaxy, or what Hubble called it, the Andromeda Nebula.
The original version of the Hubble diagram
Additionally to his distance measures of 46 galaxies Hubble further took measurements from Vesto Slipher of their escape velocity. This is basically the speed with which ‘the galaxies move away from Earth’ (what we now understand to be the cosmological redshift) and can be relatively easily measured by looking at the galaxies’ spectra, in which all spectral lines, previously known from lab experiments, are shifted by the same amount. When Hubble plotted the escape velocity of galaxies over their distance (we call this a Hubble diagram), he noticed something interesting:
The further galaxies are away from our position, the faster they move away.
This was a pretty radical idea as it proved that the Universe is not a static place at all as was widely believed before. For example, Einstein had introduced an additional term into his cosmological formula in general relativity to make his universe static/non-dynamical (something Einstein called the biggest blunder of his life after he had seen Hubble’s data. Funnily enough, this constant is now back in there to explain the accelerated expansion of the universe. It resembles the ‘dark energy’). Instead, this effect means that either the Earth is in a very special spot of the Universe where everything is flying away from it (a thought that many people, amongst them Einstein, considered wrong. The hypothesis that there is nothing special about the place where the Earth is other than that it is where we happen to live, is one of the basic fundamentals of cosmology) or there was a time in the past when everything was at the same point, much like in an explosion. Of course, we now know it was not an explosion in the traditional sense, but the beginning of time, the Big Bang.
Of course, as with most big new discoveries, these new findings were heavily discussed, not many people believed in them in the beginning. One after another, people started believing in Hubbles results, though, and the view that astronomers have on the universe changed completely. The Big Bang Theory (besides being a brilliant TV series) is now the generally accepted picture today.
As a small anecdote on the side: Due to errors in his distance measurements, Hubble measured the expansion parameter (the Hubble constant) to be 500 km/s/Mpc, which for today’s measurements is a pretty bad value, actually. After new, better data and improved data analysis were used, there were 2 big groups of people debating the real value, some said it was 50 km/s/Mpc, some others said it was 100 km/s/Mpc. For the past 10-15 years, this battle seems solved Solomonically, the value is now assumed to be just inbetween these values, somewhere between 70 and 75 km/s/Mpc. So, although Hubble was very wrong in the number that came out of his measurements, he somehow got the principle spot on.
Using the images that he had taken for his work, Hubble also came up with a system to classify these nebulae and galaxies depending on their appearance. This is what we call the Hubble sequence or the tuning fork of galaxies, and Galaxy Zoo initially used a system that was based on this diagram for their classifications.
As the Hubble Space Telescope was primarily constructed and built to observe distant galaxies (besides of course looking at objects in the solar system and interesting regions in our own galaxy), it was named after Edwin Hubble in honour of his groundbreaking work in this field.
Edwin Hubble has not only got a Space Telescope with his name, but several laws, constants and numbers are named after him, too.
Some examples:- The Hubble constant as explained above, called H0
- The Hubble time is 1/H0 and gives the approximate age of the universe. It is currently estimated to be around 13.8 billion years.
The Hubble length is c/H0and is equivalent to 13.8 billion lightyears. This is not the ’size’ of the universe, but is an important length in cosmology- The Hubble diagram as described above
- The Hubble sequence of galaxies.
- Hubble’s law
Additionally, there are:
(I think when they make you a stamp and you’ve got your own highway, you’ve really made it!)
I think that’s more or less all that I can come up with about Eddi, the post is actually quite a bit longer than I thought it would be, I’ll try to keep it shorter in the future, scout’s honour. For now, I will end with a quote from Edwin Hubble:
“Equipped with his five senses, man explores the universe around him and calls the adventure science”
With this, keep together your senses, especially seeing (the galaxies in Galaxy Zoo) and feeling (your mouse button with your index finger) and help us to do more adventurous science with the classified galaxies that you help us with (hearing, smelling and tasting are only of second order importance in astronomy, unless of course you listen to some music and have a snack while classifying  ).
Thanks and Cheers,
Boris |
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