Zodiacal Light Measurements from Balloons.

Abstract

We have used constant-level balloons floating at 110000 ft to measure photometrically and to photograph zodiacal light. A 3.5-cm-aperture telescope which has an angular field of 10~ is flown in a gondola so that the telescope is directed at a zenith angle of 800. The gondola is rotated in azimuth at an angular speed of 1 revolution in 5 minutes by an auxiliary rotator attached to the balloon. The telescope contains a rotating polaroid which turns at a speed of 10 rev/ minute. The field lens of the telescope produces an image on the photo surface of an EMI 9514B multiplier. The output of the multiplier modulates the frequency of a GMD radiosonde trausmifter. The stability of the balloon at ceiling is good enough so that the rotation speed of the gondola is essentially determined by the rotator. We have made five partially or completely successful flights prior to sunrise at Minneapolis and during the lunar first quarter. The results of the polarization and intensity measurements will be discussed. In one flight we carried a camera in which the film was continuously advanced to compensate for the gondola rotation. We were able to photograph the zodiacal light at 110000 ft in this flight. The principal advantage of studying zodiacal light from balloons is that the atmospheric extinction even on the horizon is only 20% and it is therefore possible to look at smaller solar elongation angles without interference from the atmosphere. % and it is therefore possible to look at smaller solar elongation angles without interference from the atmosphere.

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