The first telescope was a spyglass built by a Dutch optician in 1609. A few months later, Galileo Galilei created a better version and is often erroneously credited with inventing the telescope. Regardless of who gets the credit, the telescope's greatest legacy is that it has introduced us to the Universe. Soon after astronomers turned their telesopes to the heavens, many discoveries were made that completely changed how we view the universe and our place in it. Four "planets" were found orbiting Jupiter, sunspots were observed, and features were seen on the moon. Imagine seeing the craters on the moon for the first time ... out goes the ever popular cheese theory!
But the most monumetally important change was the observation of the phases of Venus. The Ptolemy earth-centered model had reigned supreme for centuries and had been ordained by the Catholic Church to be sacrosanct. In Ptomely's model, the sun and planets revolved about the earth while making circles (called epicycles) within the orbits. Mathematically, this works quite well to explain the apparent motion of these bodies. However, the observed phases of Venus put that model to rest and supported the Copernican sun-centered model. Galileo supported the denounced Copernican theory and for that he suffered. He publicly recanted, but not in his heart.
All telescopes consist of two parts; the objective and the eyepiece. The objective forms a real image of the object being observed and the eyepiece acts as magnifying glass for that image. There are two types of telescopes, the refractor and the reflector. For the refractor, the objective is a a refracting convergent lens. (In this week's lab, you will construct a refracting telescope.) For the reflector, the objective is a convergent mirror. The eyepiece for both types is usually a series of lenses that act as a magnifying glass to view the image formed by the objective. You'll find more info at the links provided and you'll be well-versed in constuction by the end of the next lab. Let's look at a few famous telescopes.
The Yerkes Big 40-inch
Yerkes Observatory, located in Williams Bay, Wisconsin and operated by University of Chicago, has a 40" refractor, the largest refracting telescope ever built. The objective lens is 40 inches in diameter. It was built in 1892 and represented quite a technological challenge for the time. Although pouring and cutting a lens of this magnitude was challenging enough, it was even more of a challenge to support the weight of the lens and a equally heavy spectrograph at the other end. A 50 ton cast iron pedestal column was built to support the steel "tube" that holds the lens. The picture to the right was taken during construction. You can see the column pedestal and part of the tube. Construction was completed in 1897 and the observatory has been observing the heavens ever since.
Mount Palomar
The Hale telescope located at the Mount Palomar Observatory in California has a 200" diameter mirror. Construction of the mirror and the observatory began in 1936, but was not completed until 1947. The mirror was poured by Corning Glass Works and weighed 20 tons. After years of grinding and polishing into the perfect parabolic shape, it weighed only 14.5 tons. The telescope "tube" is the spider web structure seen in the picture at the top of the page. An observing cage is located at the top end, at the prime focus point. Two or three astronomers can sit in the cage. Originally, someone had to be there to monitor the image and correct for drift. That is now done electronically.
Although the Hale telescope still holds the record for the largest single mirror, the Keck Observatory at Mauna Kea, Hawaii boasts a greater overall mirror area. However, it achieves this greater area with a clever multiple mirror design.
Hubble Space Telescope
If you watch the news at all, you've probably heard about the Hubble Space Telescope (HST). Most probably, you heard about the faulty optics design. That flaw was corrected soon after with the first Space Shuttle visit. Located in a low orbit about 600 km above the earth, the HST was many decades in design and construction. Although the original idea was to bring the HST back to earth every few years for maintenance and upgrading, it soon became clear that the cost and structural damage from re-entry stress made this unfeasible. So why all the expense to put into space a telescope that is quite modest compared to many earthbound telescopes?
The earth's atmosphere is the greatest limiting factor to how well a telescope can resolve images. Even on a clear night, atmospheric turbulence results in a varying index of refraction that makes images swim and blur. Located above the earth's atmosphere, UVI's 15" telescope at Etelman Observatory would outperform all other earthbound telescopes! The gallery of images that the HST's 3 cameras can achieve are truly inspiring. The image to the right was taken by the HST when comet Shoemaker-Levy smashed into Jupiter. You can clearly see four impact regions. No earthbound telescope could create an image that clear. The HST image from the Eagle Nebula is a great example of the HST's resolution.
One discovery that really suprised Galileo and the other astronomers of his time was that there were many times more stars than the naked eye could observe. But they still looked like stars ... points of light with no resolvable shape. The reason is quite straight forward. The nearest star, Alpha Centauri, is roughly the size of our sun. At it's distance of 4.3 light years, the diameter of the star subtends an angle of roughly .004 arc seconds. The best ground telescopes today can resolve an object to only about 1 arc seconds of resolution. HST's 2.4-meter reflecting telescope has far better resolution, but still not enough to actually see stars as a disc.
Last year, visiting physics professor Dr. Thomas Bruekner gave a Seminar on the HST. It has several links to some very nice photos taken by the HST, including a before and after corrective optics link.
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Questions:
What discovery made Galileo instantly famous? (It had nothing to do with telescopes!)
Why is a comparably sized refractor more expensive that a reflector?
How long and how heavy is the "tube" for the Yerkes Observatory telescope?
How long did the 200" Hale mirror take to cool after being poured?
The first telescope was a spyglass built by a Dutch optician in 1609. A few months later, Galileo Galilei created a better version and is often erroneously credited with inventing the telescope. Regardless of who gets the credit, the telescope's greatest legacy is that it has introduced us to the Universe. Soon after astronomers turned their telesopes to the heavens, many discoveries were made that completely changed how we view the universe and our place in it. Four "planets" were found orbiting Jupiter, sunspots were observed, and features were seen on the moon. Imagine seeing the craters on the moon for the first time ... out goes the ever popular cheese theory! 
Yerkes Observatory, located in Williams Bay, Wisconsin and operated by University of Chicago, has a 
If you watch the news at all, you've probably heard about the Hubble Space Telescope (HST). Most probably, you heard about the faulty optics design. That flaw was corrected soon after with the first Space Shuttle visit. Located in a low orbit about 600 km above the earth, the HST was many decades in design and construction. Although the original idea was to bring the HST back to earth every few years for maintenance and upgrading, it soon became clear that the cost and structural damage from re-entry stress made this unfeasible. So why all the expense to put into space a telescope that is quite modest compared to many earthbound telescopes? 
The earth's atmosphere is the greatest limiting factor to how well a telescope can resolve images. Even on a clear night, atmospheric turbulence results in a varying index of refraction that makes images swim and blur. Located above the earth's atmosphere, UVI's 15" telescope at Etelman Observatory would outperform all other earthbound telescopes! The 