The zodiacal light

After a discussion of the problems connected with a photometry of the zodiacal light, observational results according to measurements with modern equipment are presented (Sections 1 and 2). Then a review of different investigations concerning the determination of composition and density of the interplanetary matter is given (Sections 3 and 4). The problem of deriving interplanetary electron densities from zodiacal light observations is discussed and it is shown that an unambiguous solution at present is not available. An upper limit of 400 electrons per cm ³ for the density at 1 A.U. distance to the Sun follows from spectroscopic observations (Section 4).