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Sparrow, J. G.

Publications and source records attributed to Sparrow, J. G..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Zodiacal light as an indicator of interplanetary dust

The most striking feature of the night sky in the tropics is the zodiacal light, which appears as a cone in the west after sunset and in the east before sunrise. It is caused by sunlight scattered or absorbed by particles in the interplanetary medium. The zodiacal light is the only source of information about the integrated properties of the whole ensemble of interplanetary dust. The brightness and polarization in different directions and at different colors can provide information on the optical properties and spatial distribution of the scattering particles. The zodiacal light arises from two independent physical processes related to the scattering of solar continuum radiation by interplanetary dust and to thermal emission which arises from solar radiation that is absorbed by interplanetary dust and reemitted mainly at infrared wavelengths. Attention is given to observational parameters of zodiacal light, the methods of observation, errors and absolute calibration, and the observed characteristics of zodiacal light.

Weinberg, J. L.↗
NASA NTRS1977

Ten-color Gegenschein-zodiacal light photometer

A ten-color Fabry photometer was used during Skylab missions SL-2 and SL-3 to measure sky brightness and polarization associated with zodiacal light, background starlight, F region airglow, and spacecraft corona. A brief description is given of the design, calibration, and performance of the instrument.

Sparrow, J. G.↗
NASA NTRS1976

Pioneer 10 observations of zodiacal light brightness near the ecliptic - Changes with heliocentric distance

Sky maps made by the Pioneer 10 Imaging Photopolarimeter (IPP) at sun-spacecraft distances from 1 to 3 AU have been analyzed to derive the brightness of the zodiacal light near the ecliptic at elongations greater than 90 degrees. The change in zodiacal light brightness with heliocentric distance is compared with models of the spatial distribution of the dust. Use of background starlight brightnesses derived from IPP measurements beyond the asteroid belt, where the zodiacal light is not detected, and, especially, use of a corrected calibration lead to considerably lower values for zodiacal light than those reported by us previously.

Hanner, M. S.↗
NASA NTRS1976

The S sub 10 /V/ unit of surface brightness

Some discrepancies in the use of the unit of zodiacal light measurements - S sub 10 (V), which is the equivalent number of tenth magnitude stars of solar spectral type per square degree - are discussed. It is suggested that: (1) the S sub 10 (V) unit be understood to represent 10th magnitude solar (G2V) stars per square degree at mean solar distance, (2) the V refers to the visual color in the UBV system defined by Johnson and Morgan (1953), (3) the apparent solar visual magnitude be taken as -26.73 and the B-V index as .63, (4) the solar spectral irradiance values of Labs and Neckel (1970) be used, and (5) when using Vega as a standard to obtain brightnesses in S sub 10 (V), +.04 be used as its magnitude at all wavelengths and the irradiance values of Hayes and Latham (1975) be used.

Sparrow, J. G.↗
NASA NTRS1976

Polarization of the zodiacal light - First results from Skylab

A brief description is given of the Skylab ten color photoelectric photometer and the programs of measurements made during Skylab missions SL-2 and SL-3. Results obtained on the polarized brightness of zodiacal light at five points on the antisolar hemisphere are discussed and compared with other published data for the north celestial pole, south ecliptic pole, at elongation 90 degrees on the ecliptic, and at two places near the north galactic pole.

Sparrow, J. G.↗
NASA NTRS1975

The Skylab ten color photoelectric polarimeter

A 10-color photoelectric polarimeter was used during Skylab missions SL-2 and SL-3 to measure sky brightness and polarization associated with zodiacal light, background starlight, and the spacecraft corona. A description is given of the instrument and observing routines together with initial results on the spacecraft corona and polarization of the zodiacal light.

Weinberg, J. L.↗
NASA NTRS1975

Variations in Gegenschein polarization

Claims made by Bandermann and Wolstencroft (1974) that angular structure and day-to-day variations of the polarized component of the zodiacal light were observed near the antisolar point are shown to be unsubstantiated. The data obtained by Bandermann and Wolstencroft are reviewed together with the instruments they used. It is shown that the incorrect results reported were due to observation errors.

Sparrow, J. G.↗
NASA NTRS1975

Solar radiation induced rotational bursting of interplanetary particles

It is suggested that the magnitudes of the two radiation-induced rotational bursting mechanisms (Radzieskii effect and windmill effect) have been overestimated and that they do not work significantly faster than the Poynting-Robertson effect in removing interplanetary particles. These two mechanisms are described, and serious doubts are raised regarding the derivation of their radiation pressure-torque proportionality constants, which are required for calculating their magnitudes. It is shown that both mechanisms will cause the alignment of elongated particles and, consequently, the polarization of zodiacal light. Since no positive polarization has been measured at the antisolar point, it is concluded that the magnitudes of the rotational bursting mechanisms are smaller than that of the Poynting-Robertson effect.

Sparrow, J. G.↗
NASA NTRS1974

Is the zodiacal light intensity steady

It is pointed out that conclusions reported by Sparrow and Ney (1972, 1973) could be confirmed in an investigation involving the refinement of OSO-5 data on zodiacal light. It had been found by Sparrow and Ney that the absolute value of both the surface brightness and polarization of the zodiacal cloud varied by less than 10% over the 4-yr period from January 1969 to January 1973.

Burnett, G. B.↗
NASA NTRS1972

Observations of the zodiacal light from the ecliptic to the poles.

The brightness and polarization of the zodiacal light have been measured from the satellite OSO-5, using two photometers of effective wavelengths 4180 and 6820 A. The satellite configuration restricts the observations to ecliptic longitudes close to 90 deg, but measurements have been made from the ecliptic to the poles. On the ecliptic, the intensity of the zodiacal light was found to be 117 S10 (blue) and 315 S10 (red) with polarizations of 16.5 and 15 per cent, respectively. At the ecliptic poles the zodiacal intensity was 35 S10 (blue) with 20 per cent polarization. No temporal changes in zodiacal light have been found nor any significant differences in the intensities in the two hemispheres. The direction of polarization of the zodiacal light has been shown to be H-pass radial.

Sparrow, J. G.↗
NASA NTRS1972

Polarization of the diffuse galactic light.

Polarization measurements made from the satellite OSO-5 show that the polarized intensity in the direction of the Scutum arm of the Galaxy is different in intensity and direction of the polarization from that observed due to the zodiacal light. The observations are consistent with polarized diffuse galactic light superposed on the zodiacal light. The results are interpreted in terms of a model in which the galactic starlight is scattered by interstellar dust.

Sparrow, J. G.↗