Lookout Mountain (Los Angeles County, California)

Lookout Mountain in Los Angeles County, California is a 6,812 foot (2,076 m)[1] peak on the shoulder of Mount San Antonio ("Mount Baldy").

The peak was used by Albert A. Michelson to measure the speed of light in 1925–1929. To do so, a 21.5 mile baseline was established in 1923 by U.S. Coast and Geodetic Survey, with accuracy of 1 part in 11 million, in Pasadena at the base of Mount Baldy, roughly to Rancho Cucamonga at the base of Mount Wilson.[2][3][4] It may have been the most accurate baseline ever determined, at the time.[5][6][7] Coast and Geodetic Survey then used the baseline to triangulate the distance to the Mount Wilson Observatory, with distance error about 1 part in 5 million,[8] and Michelson measured light travel time between the stations with a rotating mirror apparatus.[9] The concrete piers on Lookout Mountain used for the Michelson observations still exist.[7]

The first fire lookout in the Angeles National Forest was built there in 1914 and stood until it burned in 1927.[10]

References
  1. United States Geological Survey 1:24,000 topographic quadrangle O34117b6 "Mount Baldy", benchmark "Antonio"
  2. Garner 1949, p. 68-69.
  3. Timeline: Historical highlights from Mount Wilson Observatory’s first 100 years, Mount Wilson Observatory, retrieved 2018-05-10
  4. Milestones of the Survey, National Geodetic Survey, June 5, 2017
  5. Dracup 1994.
  6. Daniel Medina (February 3, 2014), Higher Beauties: The Discovery of the Speed of Light in the San Gabriels, KCET
  7. "The Mount Wilson-Mount San Antonio measurements (1922 – 1926)". Theotherhand.org. Retrieved 12 December 2014.
  8. Garner 1949, p. 74.
  9. Michelson 1927.
  10. Creighton 2009, p. 27.

Sources

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