After passage through the asteroid belt the Pioneer 10 imaging photopolarimeter observed integrated starlight and diffuse galactic light for the first time in the absence of zodiacal light. Brightnesses in the blue are presented with and without individually resolved stars for regions of the sky observed when Pioneer 10 was 4.64 AU from the sun. The Pioneer 10 and 11 asteroid-Jupiter probes have provided the first opportunity to determine the spatial distribution of interplanetary dust beyond I AU and to map the background starlight in the absence of the atmospheric radiations and of zodiacal light, two of the primary objectives of the Pioneer 10 and 11 zodiacal light experiment. In this paper we present the results of background starlight observations obtained by Pioneer 10 beyond the asteroid belt and outline the methods and results of removing the effects of individually resolved stars. In the following paper [Hanner et al., 1974] we determine the spatial extent of zodiacal light and examine the contribution of the asteroid belt to the observed ß zodiacal light. 60 , 55 50 45 40 i=l.o 35 2.5 20 15 I0 ß ß ß 75 125 • ß ß ,oo. ß 150 125

No abstract

Two Nike-Apache payloads were launched into noctilucent cloud (NLC) displays from Esrange, Sweden in the summer of 1971 and two in the summer of 1973. A two-color photopolarimeter was part of the multiexperiment payload that included the Pandora collector of Dudley Observatory. The absolute brightness and degree of polarization are used to determine the size and number density of NLC particles. The Pandora collection size distribution and two arbitrary size distributions of ice, iron, and nickel are compared with the observations. The observed brightness and polarization suggests that the particles are principally less than 0.13-t•m radius with number density of 106 particles/m 3. The difference between the optical and the collection results suggests that either a large number of particles are undetected by collection or a significant number of the particles are the result of nucleation on complex ions. Two Nike-Apache payloads were launched at Esrange, Sweden, into noctilucent cloud (NLC) displays on the nights of July 31 and August 1, 1971, and two on the night of August 1, 1973. A two-color photopolarimeter was part of a multiexperiment payload consisting of the Pandora collector from Dudley Observatory [Hallgren et al., 1973], a plasma impact detector from Max Planck Institut ffir Kernphysi•k at Heidelberg, Germany [Rauser and Fechtig, 1973], and an acoustic particle impact detector from Lund Observatory in ß Lund, Sweden [Lindblad et al., 1973]. In 1971 the first payload (14.468) observed an NLC layer on ascent and descent. The second payload (14.469) indicated no NLC layer, although a polarimeter of Witt et al. [1971] launched 30 rain later observed a distinct NLC layer. This dynamic nature of the NLC observations was further confirmed when in 1973 the two payloads (14.515 and 14.516), launched 30 min apart, observed a Significant brightness difference. INSTRUMENT The optics consist of a single 5.5-cm-diameter lens, a Polaroid, and a bifurcated light guide (Figure 1). Two interference filters centered at 5400 and 4100 A with a 50-A halt'power band pass exclude intense atmospheric emission lines. The electronics for each color consists of a photomultiplier operating at 106 gain and a 6-decade current electrometer with a 0-to 5-V output signal. The instrument is axially mounted, and a 4-to 6-rps Payload spin rotates the Polaroid. The instruments were basically identical in both series of flights. The 1971 photopolarimeters had a 1 ø full angle field of view and a minimum detectivity of 1 x 10-•' W cm-'" sr-• A-• For the 1973 flights a field of view of 2.5 ø and low dark current photomultipliers improved the signal to noise ratio at the NLC and lowered the minimum detectivity to 4 X 10 -•4 W cm-'" sr-' A-•. The sunshield and optical system reduced stray light to less than 4 X 10-TM W cm-'" sr-x A-• up to a solar aspect angle of 77 ø in 1971 and 65ø in 1973 [Leinert; 1971]. The brightness response and polarization characteristics of the instrument were measured before and after each flight. In addition to compo...

No abstract

Photographs taken with the High Altitude Observatory's White Light Coronagraph (Skylab experiment SO52) are shown to contain information on the sizes and velocities of contaminant particulates around Skylab. Sizes as small as 5 microm (radius) are derived for particles as far away as 200 m from the spacecraft. The random error in the size derivation is about 30%, and no particle larger than 120 microm was observed. Transverse velocities are determined to within 0.08 m sec(-1) and radial velocities to within 9 m sec(-1). The S052 data bank contains about 3500 contaminated frames from which the nature of the Skylab environment can be inferred.