24 Inch Optical Telescope

The 24-inch telescope currently utilized by the Telescope In Education (TIE) program has a distinguished history. Designed and built by Caltech in the early 1960's under the watchful eyes of Jim Westphal (former director of Palomar Observatory), Bruce Rule, and Bruce Murray (former director of NASA's Jet Propulsion Laboratory), the telescope was used to investigate the Moon and prove that the lunar surface was solid rather than covered by a thick layer of dust. A thick layer of fine dust would have been a hazard to astronauts landing on the Moon during the Apollo missions.

The telescope was designed as a 24" f / 16 Cassegrain telescope. The mirrors were made by Perkins and Elmer. There were two secondary mirrors made: One was larger and used for visual and photographic observations. The second mirror was smaller because it was housed in a special fixture that could move the mirror at about 15 cps for accurate infrared observations. The first secondary mirror was destroyed in an accident during an observing run. The second mirror, although slightly undersized, continues to function well on the instrument. The 24" telescope has been thoroughly refurbished and reconfigured to f / 3.5 with a Newtonian focus in order to operate with the Santa Barbara Instruments Group (SBIG) ST-6 and ST-8 CCD electronic cameras.

Many notable organizations are responsible for making automation of the 24" telescope a success: Mount Wilson Institute reconditioned the Observatory dome and provided the current location of the 24" telescope at Mount Wilson Observatory, California. Caltech has loaned the TIE program the 24" reflecting telescope. Meade Instruments donated a 10" f / 6.3 Schmidt-Cassegrain Telescope and accessories as a finderscope for the system. Much of the telescope tube rehabilitation and early software testing came from Farpoint Research. The current remote operation software was been developed by Software Bisque using "TheSky" astronomy software. A new, extremely accurate control system for the 24" telescope, was developed and tested by Merlin Controls.

TECHNICAL DATA

The 24" telescope has a diffraction limited resolution of approximately .23 arcseconds at a wavelength of 550nm. The full width half maximum of the point spread function (PSF) is very nearly the same as the radius of its first dark ring, so these two measures of resolution are essentially equivalent.

A 6" f/15 refractor telescope mounted on the 24" telescope has a diffraction limited resolution of approximately .75 arcseconds for planetary imaging.

The Santa Barbara Instruments Group (SBIG) ST-6 CCD camera has pixels which are about 23 x 27 microns. At the Newtonian focus (focal length = 213.4 cm) they subtend at an angle of approximately 2.5 arcseconds. This is 10 times as large as the diffraction limit, so that at this focus the CCD limits the resolution. Although opinions differ regarding the effective size of a resolution element in a photographic emulsion, a CCD array of 25 micron pixels is about equivalent to a film resolution of 15-20 lp/mm. The ST-6 CCD consists of an array of 375 X 242 pixels. At the Newtonian focus of the 24" telescope, this yields a field of view of about 13.9 X 10.5 arc minutes.

The high resolution SBIG ST-8 CCD camera has an array of 1020 x 1530 pixels (each pixel = 9 microns). When used on the 6" f / 15 refracting telescope, it subtends .8 arcseconds per pixel. When the high resolution camera is used on the 24" reflecting telescope it subtends .9 arcseconds per pixel. On the 24" telescope its primary purpose is to conduct photometry and astrometry. On the 6" refractor the camera's primary purpose is for planetary imaging.