The Spectrum of the Zodiacal Light

Abstract

SINCE the time when Cassini published his observations of the Zodiacal Light, in 1682, the question as to the nature and origin of this peculiar phenomenon has been constantly recurring. Visual observers were ever at variance on the subject, some holding the view that the Light was a terrestrial adjunct, others that it was a sola-appendage. Visually, the matter is a difficult one to decide, for no optical power may be used because of the lack of contrast between the Light and its background of sky. Photography is similarly placed out of court, but it was expected that the question would be solved by the spectroscope. This expectation has never yet been realised absolutely, but the results recently published (Lick Observatory Bulletin, No. 165) by Dr. Fath clarify matters considerably.