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| Add Photo — Add Link — Add Commentary — Correct this page — Print | | Near Pasadena in Los Angeles County, California — The American West (Pacific Coastal) |
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Michelson Pier on Mount Wilson
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By Roger W. Sinnott, June 4, 2012 | |
| | | 1. Michelson Pier on Mount Wilson Marker | | |
Inscription. On this pier in 1926
Albert Abraham Michelson
measured the velocity of light by means of a
beam of light transmitted to
Mount San Antonio
and reflected back to this station
Location. 34° 13.353′ N, 118° 3.475′ W. Marker is near Pasadena, California, in Los Angeles County. Marker can be reached from Mount Wilson Road. Click for map. Marker is within the grounds of Mount Wilson Observatory, on the left when traveling south on an unnamed service road. The marker is about 125 yards NNW of the astronomers’ residence (called the Monastery), and 25 yards north of one of the smallest observatory domes on the mountain. Marker is in this post office area: Pasadena CA 91107, United States of America.
Other nearby markers. At least 8 other markers are within 9 miles of this marker, as the crow flies. Benjamin Davis Wilson (approx. ¼ mile away); Harvard’s Mount Wilson Station (approx. 0.3 miles away); Christmas Tree Lane (approx. 5.3 miles away); Santa Anita During World War II (approx. 5.8 miles away); Seabiscuit (approx. 5.9 miles away); Pacific Asia Museum (approx. 7.1 miles away); The Gamble House (approx. 7.7 miles away); The Trails Restaurant (approx. 8.4 miles away). Click for a list of all markers in Pasadena.
Regarding Michelson Pier on Mount Wilson. | | | | 
By Roger W. Sinnott, June 4, 2012 | |
| | | 2. From Marker Looking Northeast | | Through the hole in the trees you can see Mount San Antonio, popularly called Old Baldy, 22 miles from Mount Wilson. | | |
American physicist Albert Abraham Michelson (1852-1931) made a number of measurements of the speed of light during his lifetime. The best of these, in 1924-26, used equipment set up at this spot on Mount Wilson and at a corresponding station on Mount San Antonio, also called Baldy, 22 miles away. To help in the determination, the U.S. Coast and Geodetic Survey measured the spacing between the two stations to within 1 inch.
The apparatus at Mount Wilson consisted of a rapidly spinning disk with 8, 12, or 16 flat mirrors equally spaced around the rim. Light from a powerful arc lamp bounced off this spinning rim, traveled from Mount Wilson to Baldy, was reflected back, and bounced again off another part of the same spinning rim. The deflection of the return beam was used to calculate the light-travel time for the round trip.
Michelson’s final value for the speed of light was 299,796 ± 4 kilometers per second, which compares quite favorably with today’s adopted value of 299,792.458 km/sec.
Michelson is even better known for the famous Michelson-Morley experiment of 1887. Although it failed to show the “ether drift” Michelson was looking for, it helped to pave the way for Einstein’s special theory of relativity (1905).
(The above details of Michelson’s apparatus are adapted from K. D. Froome and L. Essen, The Velocity of Light and | | | | 
By Roger W. Sinnott, June 4, 2012 | |
| | | 3. Telephoto View of Baldy | | |
Radio Waves, Academic Press, 1969.)
Also see . . . Albert A. Michelson - The Nobel Prize in Physics 1907. Life and work of A. A. Michelson. (Submitted on July 8, 2012, by Roger W. Sinnott of Chelmsford, Massachusetts.)
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1897 | |
| | | 4. A. A. Michelson | | Image from Wikimedia Commons. | | |
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By Roger W. Sinnott, June 4, 2012 | |
| | | 5. Looking South from Marker | | In the background is one of the smallest observatory domes on Mount Wilson. | | |
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Credits. This page originally submitted on July 8, 2012, by Roger W. Sinnott of Chelmsford, Massachusetts. This page has been viewed 124 times since then. Photos: 1, 2, 3, 4, 5. submitted on July 8, 2012, by Roger W. Sinnott of Chelmsford, Massachusetts. • Syd Whittle was the editor who published this page.
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