2. Astronomy
  3. Large Observatories

Mount Wilson Observatory

The next step for George Hale after building and managing Yerkes Observatory was to head to Pasadena CA in search of better skies to continue his astro physics studies. As with most astronomers today he was looking for better air and more light. It seems we are always looking for more light. Mount Wilson, in the hills just north of Pasadena, provided Hale with more stable air and more clear nights to make his observations than he found in southern Wisconsin. The Mount Wilson Observatory (MWO) became a world leading observatory and produced significant work for almost ten decades. 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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09, All of the parts for the telescopes and observatories had to be carried up a steep and winding 9.5 mile road to the top of Mount Wilson. This truck is loaded with the main part of the 100” telescope tube that is 11 feet wide. The truck was custom made for Mt Wilson Observatories and use a gas engine to run a generator that powered electric motors on all four wheels. Both front and back wheels could steer.
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09, All of the parts for the telescopes and observatories had to be carried up a steep and winding 9.5 mile road to the top of Mount Wilson. This truck is loaded with the main part of the 100” telescope tube that is 11 feet wide. The truck was custom made for Mt Wilson Observatories and use a gas engine to run a generator that powered electric motors on all four wheels. Both front and back wheels could steer.

Wilson10002B

  • 01, This aerial photo of Mount Wilson shows the layout of the five major instruments built for that observatory. The three on the left are dedicated to solar observations and the two on the right are larger reflecting telescopes used for mainly studying faint objects. A major part of Hale’s work was spectroscopic study of the sun.
  • 02, The next large telescope Hale built was the 60 inch reflector. His Dad paid for the fabrication of a 60” mirror blank when Hale was still working at Yerkes. But by that time he knew he had to find a better location for an instrument of that size. Large optics are sensitive to temperature changes and that was always a consideration in the construction of observatories. Notice the gap at the base of the 58 foot diameter dome. At first a canvas outer dome was added over the main dome structure to shield it from sun light during the day and provide some ventilation to keep the inside of the observatory closer to night time temperatures. The canvas was replaced with sheet metal in 1912.
  • 03, This is the 60” reflecting telescope. The 60” diameter main mirror is mounted in the bottom of the 18’ long by 6.5’ diameter blue tube. Secondary mirrors are mounted at the top end of the truss tube. When setup for Cassegrain focus the star light would reflect off a second mirror at the top of the tube and down to a third mirror just in front of the main mirror and then out to the side of the tube where you see the white disk. The declination drive can be seen on the left side of the telescope. First Light was December 8, 1908 and at that time it was the largest telescope in the world.
  • 04, When you changed the optical setup you didn’t just change a mirror, you change the whole top of the telescope. The assembly on the left is used for the Newtonian focus. You can see the diagonal mirror in the middle of the tube is covered to keep it safe and clean. This was the first telescope to use the Coudé Focus, which is a very long focus to a stationary spectrograph mounted along the polar axis. This focus passed through the hollow polar shaft.
  • 05, The moving parts of the telescope weighed 22 tons, so a mercury bearing was designed to support the load while the scope was rotated very smoothly to accurately track the stars during long exposures. A 10 foot diameter steel float weighing 4 tons was mounted on the end of the 15’ long, 4.5 ton (hollow) polar shaft. 650 pounds of mercury was poured into the 1/8” gap between the trough and float which supported 21.5 tons of the telescope. The rest of the weight was carried by the bearings on the polar shaft. Once during an earthquake in the LA area some of the mercury spilled out.
  • 06, This photo shows the polar drive gear and clutch system. The gear seen with the straight teeth is really used to slew the scope into position. The polar dive gear is seen just at the lower right edge of the photo. The worm gear is mounted in the blue framework at the bottom of the photo. This 2 ton, 10 foot diameter gear has 1080 teeth around its circumference.
  • 07, This close up view of the bottom of the 60” scope shows some spectroscopic gear mounted at the Cassegrain focus. The dark blue tube on an angle (right side) is a weight system used to take out backlash for the declination drive gears. Both declination and polar drives had anti-backlash weight systems.
  • 08, This is the dome for the 100” Hooker Telescope. The vane that goes up the back side of the dome helps protect personnel that may have to clime the ladder for maintenance during high winds or bad weather.
  • 09, All of the parts for the telescopes and observatories had to be carried up a steep and winding 9.5 mile road to the top of Mount Wilson. This truck is loaded with the main part of the 100” telescope tube that is 11 feet wide. The truck was custom made for Mt Wilson Observatories and use a gas engine to run a generator that powered electric motors on all four wheels. Both front and back wheels could steer.
  • 10, The 100” telescope is supported by a yoke mounting with mercury floatation bearings on each end of the yoke to support the 100 tons of moving telescope mass. Note all the rivets in the structure. This was built before welding had become common place in ship building. These apart were manufactured in Fore River Shipyards in Quincy, Massachusetts. Some parts were too large to send by train and had to go by ship through the Panama Canal. First Light was November 2, 1917 and at that time it was the largest telescope in the world and would keep this status for about three decades.
  • 11, Like the 60” reflector the top end of the telescope is changed when you change the optical arrangement. This is the Coudé Focus assembly and the Newtonian Focus assemble is in the background next to the person in the shadows. These assemblies are 11 feet across.
  • 12, A “U” shaped platform attached to an elevator like mechanism built into the frame on either side of the dome slot provides access to the top of the telescope for operation and maintenance work. There is a mechanism that uses cables to keep the platform level as it move up along the curved dome frame. It actually swings a little when you walk around on it because it is suspended with cables.
  • 13, This photo shows the famous astronomer Edwin Hubble sitting on the observers platform operating controls at the Newtonian Focus. His right and left hands are on the guiding controls for the camera. The camera was actually moved in two orthogonal directions with those controls to compensate for errors in the telescope motion. In other words he was “guiding” the camera, not the telescope. Hubble was the man that collected enough photo data to prove that the universe is expanding. He is the namesake for the Hubble Space Telescope.
  • 14, This is the Newtonian Focus for the 100” scope that Hubble was using in the previous photo. A glass plate holder is in the middle with a microscope just to the right. The astronomer would line up a star in the microscope and then use the controls around the camera to make adjustments to keep the star on the microscope cross hairs. This process was necessary to keep the image from moving on photographic plate during the long hours of exposure. A 2 foot by 3 foot Newtonian diagonal mirror is in the middle of the tube just behind the camera. The 100” mirror has a focal length of 42 feet.
  • 15, The Cassegrain Focus is on the other end of the telescope off to the north side. There is a wooden chair sitting on the adjustable platform that gives astronomers access to the Cass focus. As of the time of my visit in the early 90’s only one astronomer had been injured by falling off this platform.
  • 16, This shows a section of the 17 foot diameter polar drive gear. The original drive mechanism was like a grandfather clock type escapement mechanism powered by a two ton weight. It was later converted over to an electric motor when electric power was run up the mountain.
  • 17, This is a side view of the polar drive gear (red arrow). The smaller gear is used to slew the telescope into position. The image plane for the 134 foot focal length Coudé Focus is at the wall on the left side of the photo. The Coudé focal path passes through the hollow polar shaft to this point.
  • 18, This is the well-worn control panel located on the floor near the telescope.
  • 19, A lot of the telescope tube frame work had holds in order to keep the overall weigh down. Even so the moving parts still weighed about 100 tons.
  • 20, The larger the telescope the more critical overall balance is to controlling precision motion of the scope. The light blue tube on the right side of the yoke carries a weight that is moved by motor control. This is used to maintain balance about the declination axis.
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