The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000 Å. II. Measurement of Foreground Zodiacal Light

We present a measurement of the absolute surface brightness of the zodiacallight (3900-5100A) toward a fixed extragalactic target at high eclipticlatitude based on moderate resolution (~1.3A per pixel) spectrophotometryobtained with the du Pont 2.5m telescope at Las Campanas Observatory in Chile.This measurement and contemporaneous Hubble Space Telescope data from WFPC2 andFOS comprise a coordinated program to measure the mean flux of the diffuseextragalactic background light (EBL). The zodiacal light at optical wavelengthsresults from scattering by interplanetary dust, so that the zodiacal light fluxtoward any extragalactic target varies seasonally with the position of theEarth. This measurement of zodiacal light is therefore relevant to the specificobservations (date and target field) under discussion. To obtain this result,we have developed a technique that uses the strength of the zodiacal Fraunhoferlines to identify the absolute flux of the zodiacal light in themultiple-component night sky spectrum. Statistical uncertainties in the resultare 0.6% (1 sigma). However, the dominant source of uncertainty is systematicerrors, which we estimate to be 1.1% (1 sigma). We discuss the contributionsincluded in this estimate explicitly. The systematic errors in this resultcontribute 25% in quadrature to the final error in our coordinated EBLmeasurement, which is presented in the first paper of this series.