Thursday, June 23, 2011

The Mt. Wilson Observatory: The 100-Inch Telescope

(GPS: N34° 13.545 W118 03.430)

Last time I was crossing the bridge to get to the most famous telescope at the observatory. There are many plaques with signs about each scope around the observatory. There is usually a timeline, pictures of discoveries by the scope, write-ups of the important discoveries, and a "blue print" of the telescope. This is part of the one for the 100-Inch Telescope.From the bridge you just go to your left and around the corner in this following picture. Then there are two open doorways. You can go up either one because it gets you to the visiter room to view the telescope. In the video, I kept walking up the stairs just because I liked the effect of it, but no need to post pictures of them here.This telescope is known as the Hooker telescope because Joseph Hooker was the one who invested the money into making it. What happened in astronomy during the late 19th and 20th centuries is scientists were dependent on very wealthy philanthropists to donate and invest in observatories and their telescopes. Observatory director George Hale had to spend much time lobbying for funds rather than spending all his time doing more scientific research. Hale was always pushing for bigger telescopes. After the 60-inch scope he wanted a 100-inch telescope built. In around 1906, the 100-inch mirror was okayed for production in France. It was finished in 1908 and sent across the Atlantic. When it finally arrived Hale and others examined it with great anticipation. Unfortunately, there were bubbles in the disk and the glass was fused. This was a major let down since they realized they would not be able to use it. After thoughts of getting a new mirror, Hale decided it might work after all. So, he had the mirror grounded and polished in 1910 and finished in 1916. It was finally taken up the dirt road to Mt. Wilson on July 1, 1917. The telescope was ready and first used in November of 1917. However, due to World War I, the scope was not really used until after the war was over.What you see above is the bottom part of the telescope. The 100-inch mirror resides there. It is a reflecting telescope in that it captures the light and reflects it off the mirror for viewing. The picture below is just looking straight up the frame of the scope.
In the following picture, Edwin Hubble is on the left and James Jeans is on the right. There is a chair, known as the Hubble Chair, that can move into place to view the telescope. The scope, the dome, and the chair can move into place to view whatever part of space needs to be viewed.There is the Hubble Chair. You can see how it would movie into position. Essentially, it is the same scope that went up on 1917. I am sure there have been part replacements, etc., but the mirror and what you see is the same.There is where the dome can open up.
As I mentioned last time, the prevailing view was that the only galaxy that existed was our Milky Way Galaxy. What people believed they were seeing through telescopes were only nebulas that existed in our own galaxy. Harlow Shapley was a leading advocate of this point of view.

Edwin Hubble began using the 100-inch telescope in the 1920's. He favored the alternative hypothesis of the time that we are part of an island universe where there are many galaxies beyond our own out there in space. The problem was that during this time there was no way to gage the distances on how far these nebula were away from earth. On October 4, 1923 he was doing his nightly routine of taking pictures of various nebula when he took a picture of the "Andromeda Nebula". Hubble examined the picture later and noticed a new speck of light in the nebula. He indicated it was a nova. Then, while going through old pictures back to 1909 of the same spot he determined he had found a variable star. Not just any variable star, but a Cepheid variable star. This type of star changes its luminosity in a cycle over a period of about a month in such a way that it can be used as a "standard candle" in astronomy. Basically, a common analogy is, if you know you have a 100-watt lightbulb you can measure its brightness to determine how far away it is from you. The further it is away from you the dimmer it will be, but you can measure that based on your knowledge of how bright it would be a few feet from you.

Hubble ended up finding more Cepheid variable stars and had definite evidence that the spiral nebula they were seeing were not nebula after all, but were much further beyond our galaxy. The Andromeda Nebula was really a galaxy itself: the Andromeda Galaxy. So, from this discovery at this telescope we found out that we are just one galaxy among many in the universe.

The second discovery was done years later. By 1929, Hubble, with Milton Humason, had determined the distances to 24 galaxies. They noticed the galaxies were red shifting. By measuring the velocities of the galaxies they found out that the velocity increased the more distant the galaxy was. A galaxy 10 million light years away travels twice as fast as the galaxy 5 million light years away. Basically, the galaxies were moving away from each other at great speeds. This was the evidence that our universe is expanding, and was the foundation for the Big Bang Theory about the beginning of the universe.

I'll cover one more item at Mt. Wilson Observatory next time as I wrap this one up.

Lots of books can be found about the Mt. Wilson Observatory, Edwin Hubble, and this telescope. A good non-technical level book is Marica Bartusiak's The Day We Found the Universe. She gives all the background history needed and emphasizes that it was not just one scientist that made these discoveries, but each scientist laid down the necessary research as the foundation for the major discoveries.