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21-inch Telescope

gr/21inch.jpg

The 21-inch telescope at Lowell Observatory. Photo: Don Thompson.

Lowell Observatory inaugurated use of a new 21-inch reflecting telescope dedicated to solar studies in 1953. These included photometric measurements of the brightness fluctuations of the outer planets Uranus and Neptune (thought to be reliable reflectors of incident sunlight) and sun-like stars. The telescope is located on the western edge of the Mars Hill campus in a small stone building with a roll-off roof, and has been equipped since 1974 with a photoelectric photometer and data acquisition computer. A Lowell Observer online newsletter article describes research using the 21-inch telescope in more detail.



Lowell Telescope Specification chart

Perkins 72" Hall 42" LONEOS 31" 21"
Longitude 111° 32' 09.3" 111° 32' 07.9" 111° 32.2' 111° 32' 09.0" 111° 39' 59.2"
Latitude +35° 05' 48.6" +35° 05' 48.3" +35° 05.8' +35° 05' 54.6" +35° 12' 10.4"
Altitude 7236ft. (2206m) 7236ft. (2206m) 7236ft. (2206m) 7243ft. (2208m) 7260ft. (2213m)
Dp 72" (1.8m) 41" (1.04m) * 31/29.5" (0.79/0.75m) 20.78 (0.53m)
F/# 17.5 8.06 * 15 15.9
EFI 1256.5" (31.93m) 330.39" (8.392m) * 464" (11.78m) 332.5" (8.44m)
Scale ("/mm) 6.45 24.58 * 17.5 24.3
BFI 51.5" (1.30m) 29.9" (0.759m) * 25" (0.63m) 20" (0.51m)
Fp/# 4.18 4.05 * 5.0 3.4
FLp 300.6" (7.635m) 166.06" (4.218m) * 155" (3.94m) 70.0" (1.77m)
Dsa 16.3" (0.41m) 16.6" (0.422m) * 9.0" (0.22m) 4.6" (0.12m)
Is 284.1" (7.22m) 130.43" (3.313m) * 134.9" (3.43m) 72.7" (1.85m)
Os 68.0" (1.72m) 65.51" (1.664m) * 45.1" (1.14m) 15.3" (0.39m)
Ms 232.6" (5.91m) 100.56" (2.554m) * 109.9" (2.79m) 54.7" (1.39m)
mag 4.2 1.990 * 3.0 4.7
K1 -1.0 -1.306 * -1.00 -1.00
K2 -3.65 -14.945 * -5.01 -3.35

1) Longitude and latitude are good to about 0.2.
2) The altitudes are good to about 1 meter.
4) The Hall F/8 is a Ritchey-Chretien telescope.
5) The 31inch primary if F/5. However, it is stopped down to 29.5 inches.
6) Only the Hall F/8 has a known optimum back focal distance.
7) The conic constant is defined such that 0 is a circle and -1 is a parabola.
8) Dsa is the diameter of the axial cone at the secondary. The diameter of the secondary is 1 to 2 inches larger than Dsa.

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