It’s another entry in the Gimmick Destinations column. This time, it’s a brief stop at Palomar Observatory’s Hale Telescope. Some time back, I was driving out of San Diego and headed to an appointment north of there. I heard that Palomar Mountain was only about a 1/2 hour off the normal route and given that there was heavy traffic headed north I decided to take some back roads to reduce time and get takeout. But on the route I took, I saw some signs and maps saying which way this well-known observatory was located. I had to be quick and only stay long enough for a couple pictures . . . maybe 20 minutes or less to make my scheduled appointment just after midday.
Photo courtesy of Ben Faltinowski (2019)
After winding up Palomar Mountain, I came to the famed CalTech Observatory. It wasn’t hard to spot the dome housing the famed 200-inch Hale Telescope. There are several other smaller telescopes dotting the Observatory grounds, but today’s focus is the famed Hale one.
Photo courtesy of Ben Faltinowski (2019)
Since I only had a few minutes to take photos, I read up more about the Hale Telescope online later. The following information comes from Cal-Tech’s related site, but where noted, the photos are mine. Cal-Tech’s website says the 200-inch (5.1-meter) Hale Telescope was dedicated in 1948 and was the largest effective telescope in the world until 1993. Even so, the 200-inch Hale Telescope is still heavily used and contributes to a wide range of astronomical research including Solar System studies, the search for extrasolar planets, stellar population and evolution analysis, and the characterization of remote galaxies.
Photos courtesy of Ben Faltinowski (2019)
Astronomer and Caltech founder George Ellery Hale was the visionary behind this telescope, and he vigorously pursued funding to build the 200-inch Telescope and eventually secured the sponsorship of the Rockefeller Foundation in 1928. All aspects of building such a large and precise instrument required innovative methods and revolutionary technology, which has lead some to consider it the “moon shot” of the 1930s and 40s while Werner Von Braun was made to work on the V2 (against his will) for Germany.
Base of the Hale Telescope. Photo courtesy of Ben Faltinowski (2019)
The Hale Telescope is a reflector type, or a telescope whose primary optical element is a curved mirror—there are no lenses in the telescope itself. The Hale’s primary mirror is a 200-inch (5.1-meter) in diameter Pyrex disk that weighs 14.5 tons (13 tonnes). Its polished surface, covered with a thin layer of aluminum, is concave. The mirror’s thickness varies between 19 ⅝ inches (49.8 cm) at the center and 23 ½ inches (59.7 cm) at the outer edge.
The primary mirror’s area, about 31,000 square inches or 20 square meters, acts as a giant pupil that collects light from the Universe. Because the mirror is a paraboloid (f/3.3, focal length 660 inches or 16.76 meters), light comes to a focus near the top of the telescope at what is known as the prime focus. A camera or scientific instrument can be placed at prime focus, or a secondary mirror to reflect the light back down through a hole in the primary mirror to what is known as the Cassegrain focus (f/16, focal length 3,200 inches or 81.3 meters). Two additional light paths are also possible—by using additional mirrors, light can be directed into the coudé focus (f/30, focal length 6,000 inches or 152 meters) or to an instrument in the east arm of the telescope.
This diagram (from Wikipedia) shows a size comparison of the Hale Telescope compared to other existing ones and even newer/larger ones. The Hale held the title of largest for many years until being superceded by others, particularly the ones on Hawaii’s Mauna Key and Cerro Amazones in Chile. The Hale Telescope’s size is shown in the upper-left corner of this diagram and on the bottom shows tennis and basketball courts for size comparison. Even so, the Hale remains a major, reliable instrument for many of the world’s most renowned astronomers and students (particularly at Cal-Tech).
Cal-Tech’s website goes on to say that the Hale Telescope is used every night for astronomical research thanks to the continual development of state-of-the-art support instrumentation. This includes adaptive optics systems that correct for distortions caused by Earth’s atmosphere—known as seeing, what makes stars twinkle—to deliver sharp images comparable to those produced by space telescopes from a ground-based facility. The Hale Telescope instruments provide a wide range of imaging and spectroscopic capabilities in the optical and near-infrared parts of the spectrum.
Finally, the Cal-Tech website says that the 200-inch mirror and instruments are supported by a steel equatorial mount, which allows for east-west and north-south motion. Moving this 530-ton (481-tonne) telescope must be done precisely if astronomical observations are to be possible at all.For slewing (rapid movement) it uses two small motors: a 3-hp motor for right ascension and a 1-hp motor for declination. For tracking (keeping up with Earth’s rotation during long exposures) it is moved by a 1-hp step motor. The Hale Telescope is kept in perfect balance. As such, when instruments are changed the balance of the telescope must be adjusted.
The piers for the Hale Telescope are anchored to the bedrock 22 feet (6.7 meters) below, while the dome supports go about 7 feet (2.1 meters) into the overlying granite. The dome is 135 feet (41 meters) tall and 137 feet (42 meters) in diameter. It is a remarkable coincidence that these dimensions are similar to those of the Pantheon in Rome. The details of the dome’s structure is discussed in the architecture section of Cal-Tech’s website.
The rotating part of the dome reportedly weighs approximately 1,000 tons (900 tonnes), with a plate steel exterior and aluminum panel interior, separated by four feet (1.2 meters) to allow for an insulating layer of air. Two 125-ton (113-tonne) shutters cover the opening and slide open at night to allow light through the slit and into the telescope. The top section of the dome rotates on two circular rails, riding on 32 carriages each with four wheels. One rotation takes about 4 minutes. Rotation of the dome is driven by four 7.5 horsepower motors (30 hp total).
Among the more notable discoveries of the 200-inch Hale reflector were observing and helping Dutch astronomer Maarten Schmidt figure out the nature of quasars. He examined these bright sources of radio waves, based on information from other astronomers, because they were not sure what they were.
It is now believed that quasars are actually galaxies with overpowering supermassive black holes in their centers. They hold a tremendous amount of interest because they are considered the most luminous objects in the visible/physical universe.
The Hale Telescope has been used for numerous other astronomy observations and research beyond just quasars. It has been used to look for exoplanets (or planets outside of the Solar System), other galaxies (such as Andromeda and Sombrero), nebulas, comets, and even our own Solar System planets (such as Neptune, which is almost at opposition as of September 2019).One great challenge that the Palomar Observatory (including the Hale and other telescopes there) is the growing light pollution nearby from cities such as San Diego and Los Angeles. Efforts are in effect to curb and reduce this intrusion which could greatly limit the Hale Telescope’s capabilities over time.
As before, I only had 20 minutes to stop by and visit. As it was late morning, I only had time to snap a few pictures and pick up some related trinkets for my wife and kids. Also, the grounds are only open between 9:00 and 5:00 PM (PST) each day and is usually off limits unless you have permission by Cal-Tech and have reservations. But it’s definitely an inspiring place and would like to go visit the Hale Telescope again in the future and see the other observatories on site.
For The Great Galactic Space Gimmick, I’m Gimmick Commander Ben Faltinowski. 🚀👍 🔭🌌
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