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| Keywords: Usno-telescope-equalized-1.png en The USNO 26-inch refracting telescope is located on the grounds of the US Naval Observatory at Washington DC and is included as part of the Monday night tour when skies are cloudy This telescope has a rich history Completed in 1873 at a cost of 50 000 it was the largest refracting telescope in the world for a decade The lens and mounting were made by the renowned firm of Alvan Clark Sons of Cambridgeport MA and the great telescope was duly erected on the grounds of the old Naval Observatory site in the Foggy Bottom section of Washington It was from this site in August of 1877 that astronomer Asaph Hall discovered the two moons of Mars Phobos and Deimos with the Great Equatorial Telescope bringing the attention of the world to the USNO The move to the Observatory's present site in 1893 allowed the 26-inch lens to be re-mounted in a new dome with a new mounting designed by the Warner Swasey Company of Cleveland OH This design incorporated a rising floor to facilitate access to the eyepiece This floor is still the largest elevator in the city Today 2001 the telescope is used on every clear night to measure the parameters of double stars Over the years visual observations by astronomers using micrometers have been replaced by electronic imaging techniques By taking very short exposures with a Charge-Coupled Device CCD camera astronomers can actually use the blurring effect of Earth's atmosphere to their advantage to measure the separations and position angles of double star components The technique known as speckle interferometry is ideally suited to the 125 year-old optics of the great telescope and relatively unaffected by the urban location of the Observatory Several thousand stars are measured annually and the database of such observations added to the visual observations dating back over a century provide for one of the most concise double star catalogs in the world The telescope is also used to measure the positions of the moons of the outer planets to help refine their orbital parameters These data are vital in planning missions to such distant worlds Caption taken from http //web archive org/web/20011114201740/http //www usno navy mil/USNO26in shtml http //web archive org/web/20011114201740/http //www usno navy mil/USNO26in shtml where a low resolution copy of this image can be found Some photoshopping was necessary to remove damage to the photograph near the top of the pillar 1980 or earlier scanned by uploader from photographic print United States Naval Observatory File USNO26in-2 jpg lower resolution from USNO website PD-USGov-Military-Navy United States Naval Observatory Refracting telescopes Telescopes containing lenses ground by Alvan Clark Sons | ||||
