2. Astronomy
  3. Large Observatories

Yerkes

Yerkes Observatory was the first step that George Hale took on the way to building the 200” telescope at Mount Palomar. The main instrument is a 40” diameter telescope which today is still the largest operating refracting telescope in the world. Except for the black & white photos, the rest of the photos in this gallery were taken in the early 90’s.
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08, The two element lens was ground and polished by Alvan G. Clark (left) and is foreman Carl Lundin and installed on May 20, 1897. The ring to the left of Alvan Clark in the photo is the spacer that keeps the two lens elements about a foot apart. It was important to George Hale that this telescope be the largest in the world and be more prominent than the 36” refractor at Lick Observatory, which was already in operation. The lens assembly weighs 1000 pounds.
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08, The two element lens was ground and polished by Alvan G. Clark (left) and is foreman Carl Lundin and installed on May 20, 1897. The ring to the left of Alvan Clark in the photo is the spacer that keeps the two lens elements about a foot apart. It was important to George Hale that this telescope be the largest in the world and be more prominent than the 36” refractor at Lick Observatory, which was already in operation. The lens assembly weighs 1000 pounds.

YERKES0008

  • 01, George Ellery Hale (June 29, 1868 – February 21, 1938) was educated at MIT and had an unquenchable desire for finding out what the universe was made of. He invented the spectroheliograph for studying the composition of the sun and stars. It was his driving force that developed the 40” at Yerkes, the solar telescopes at Mount Wilson CA a long with the 60” and 100” reflecting telescopes, and began the work to build the 200” reflector at Mount Palomar. All of these telescopes were pushing the boundaries at that time and setting world records.
  • 02, The 90 foot diameter dome under construction in 1896
  • 03, Section drawing of the dome and 40” diameter telescope that is 60 feet long.
  • 04 The mounting and tube for the 40” in November 1896.
  • 05, Assembling the cast iron parts that make up the pedestal for the 40” mount.
  • 06, The clock drive parts that move the telescope to compensate for the earth’s rotation. This mechanism is located inside the mount pedestal.
  • 07, The Declination shaft is being attached to the Polar shaft. You can get a feel for the size of the parts when you see the work men on the mounting.
  • 08, The two element lens was ground and polished by Alvan G. Clark (left) and is foreman Carl Lundin and installed on May 20, 1897. The ring to the left of Alvan Clark in the photo is the spacer that keeps the two lens elements about a foot apart. It was important to George Hale that this telescope be the largest in the world and be more prominent than the 36” refractor at Lick Observatory, which was already in operation. The lens assembly weighs 1000 pounds.
  • 09, Yerkes Observatory as it appeared in the early 1990’s
  • 10, 40" telescope with 60 foot focal length.
  • YERKES_0011
  • 12, There are a number of digital readouts on the rear of the telescope to provide time and position information. The black box is a camera with a large eyepiece in the middle of the photographic frame.
  • 13, In the early 90’s they were using glass plates to photograph star clusters and measure proper motion of the stars. The yellow ring around the end of the scope tube is a hand hold use to manually move the telescope after the clutches were released. Even though the moving parts of the scope weigh 22 tons it is easy to pull around to aim the scope at an object.
  • 13B, Control Panel located on the 75 foot diameter floor that weighed 37.5 tons. The floor was actually an elevator to keep the astronomer close to the end of the scope no matter where it was pointed.
  • 14, Before electronic setting circles were invented they use very large mechanical circles to tell where the telescope was pointed.
  • 15. The clock drive uses a “worm and wheel” for the final reduction stage. The red spokes are part of the large wheel gear. There is metal (white) cover over the gear to keep it clean and prevent damage.
  • 16, The observatory engineer and I spent the day looking at all the hardware in the nooks and cranny’s around the observatory. That evening we had the 40” to ourselves and the night was clear. We raised the floor so we could look at some objects lower in the sky. This gave me a chance to see the stuff under the floor. The large motor in the cage (lower right) is used to raise and lower the 37.5 ton observing floor.
  • 17, This 1960 shot show the older shutter/aperture arrangement in front of the objective lens.
  • 17B, By the 1990’s the front end of the telescope had been modified for some different hardware.
  • 18, A few years after the telescope went into operation a crack started to develop in the front lens. At this time Alvan Clark had passed away and there was real concern about having to replace the front element and who at that time had the skill to do the job. To prevent the crack from propagating across the lens a small hole was drilled (red arrow) just in front of where the crack was heading. When the crack reached the hole the stresses were relieved and it stopped propagating. There are small pieces of black tape covering the hole.
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