Stray light observations at the 200-inch hale telescope on Palomar mountain

Measurements of low-angle scatter of the 200-inch Hale Telescope were taken to establish the amount of scatter expected at the focal plane when the telescope is pointed near the Sun. These measurements were obtained by using the Moon as a surrogate solar source, attenuated by roughly six orders of magnitude. Pointing the telescope at the Moon, and at angles ranging from 2 to 12 degrees from the Moon, the variation and sources of background light were observed at the focal plane of the existing PHARO science camera. Through the use of the pupil-imaging option on the PHARO camera, comparisons of the sky background and light scattered directly from the primary mirror into the field of view were evaluated. Sky scattering appeared to decline as the inverse square-root of the angle from the Moon, while primary mirror scattering appeared to decline much quicker, as the inverse square of the angle from the Moon.