Atmospheric Distortion

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Many people believe that astronomers want to build telescopes on tall mountains or put them in space, so they can be ``closer'' to the objects they are observing. This is INcorrect! The nearest star is over 41,500,000,000,000 kilometers (26 trillion miles) away. If you ignore the 300-million kilometer variation in the distances due to the Earth's motion around the Sun and the 12,756-kilometer variation due to the Earth's rotation, being 4 kilometers closer on a tall mountain amounts to a difference of at most 1 × 10-11 percent. Telescopes in space get up to 1 × 10-9 percent closer (again ignoring the much larger variations of the Earth's orbit around the Sun and the telescope's orbit around the Earth). These are extremely small differences---the distances to the even the nearest stars are around 100,000's times greater than the distances between the planets in our solar system. The reason large telescopes are built on tall mountains or put in space is to get away from the distortion of starlight due to the atmosphere. The atmospheric distortion is poor seeing, reddening, extinction and the adding of absorption lines to stellar spectra.

Kitt Peak National Observatory The famous observing site at the Kitt Peak National Observatory has many large telescopes including the 4-meter Mayall telescope(top right) and the McMath Solar Telescope (triangular one at the lower right). Although it is over 60 kilometers from Tucson, AZ, light pollution from the increasing population of that city has stopped the construction of any more telescopes on the mountain.

The Mauna Kea Observatory is probably the best observing site in the world. Many very large telescopes are at the 4177-meter summit of the extinct volcano. Because of the elevation, the telescopes are above most of the water vapor in the atmosphere, so infrared astronomy can be done. Kitt Peak's elevation of 2070 meters is too low for infrared telescopes.

Mauna Kea Observatory

The James C. Maxwell Telescope is in the center front of this picture of the Mauna Kea Observatory. The two white Keck 10-meter telescopes are to the left on the ridgetop next to the silver 8.3-meter Subaru telescope. Select the image to go to the Mauna Kea Observatory homepage (will display in another window).

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last updated: May 18, 2010

Is this page a copy of Strobel's Astronomy Notes?

Author of original content: Nick Strobel