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Thompson, D. T.

Publications and source records attributed to Thompson, D. T..

26 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

UBV photometry of the Galilean satellites

UBV observations of the Galilean satellites made at Lowell Observatory and Cerro Tololo Inter-American Observatory during 1973 and 1974 are reported. The dependence of brightness on solar phase angle for various faces of each satellite is determined. Significant differences in this dependence are found between different faces of the same satellite, between satellites, and between the present results and those of previous investigators. Rotational light and color-index curves are presented for the satellites and compared with earlier work. An apparent secular brightening of all four satellites between 1973 and 1974 is discussed.

Millis, R. L.↗
NASA NTRS1975

UBV photometry of asteroid 433 Eros

UBV observations of asteroid 433 Eros were conducted on 17 nights during the winter of 1974/75. The peak-to-peak amplitude of the light curve varied from about 0.3 mag to nearly 1.4 mag. The absolute V magnitude, extrapolated to zero phase, is 10.85. Phase coefficients of 0.0245 mag/degree, 0.0009 mag/degree, and 0.0004 mag/degree were derived for V, B-V, and U-B, respectively. The zero-phase color of Eros (B-V = 0.88, U-B = 0.50) is representative of an S (silicaceous) compositional type asteroid. The color does not vary with rotation. The photometric behavior of Eros can be modeled by a cylinder with rounded ends having an axial ratio of about 2.3:1.

Millis, R. L.↗
NASA NTRS1974

A search for posteclipse brightening of Io in 1973. I

Eight eclipse reappearances of the innermost Galilean satellite, Io, were observed during the fall of 1973. The measurements were made using photometers specially designed to cope with the problem of scattered light from Jupiter. Posteclipse brightening of Io was not detected and, if present, was less than our estimated detection threshold of about 0.02 mag.

Millis, R. L.↗
NASA NTRS1973

Time variation of Martian regional contrasts.

Observations of contrast changes in blue light on Mars in 1969 and 1971 are presented. Seasonal effects evidently can be evaluated from these data, although nonseasonal effects are also present. A diurnal variation is noted for certain features during both apparitions. This variation cannot be fully accounted for without considering meteorological effects. An example of a contrast reversal in ultraviolet light is presented. The suggestion is made that during the Martian season covered herein, variability of the bright areas controlled the apparent contrasts observed.

Thompson, D. T.↗
NASA NTRS1973

A new look at the Martian 'violet haze' problem. II - 'Blue clearing' in 1969.

The 1969 apparition of Mars has been extensively observed by the International Planetary Patrol Program. Using this material, the distribution of blue clearing in phase angle has been examined for four Martian bright area-dark area pairs. Arabia-Syrtis Major showed a smooth variation with a maximum at opposition. Zephyria-Mare Cimmerium showed a similar behavior except for a period around 20 deg before opposition. Memnonia-Mare Sirenum showed a rather steady decline from 20 deg before opposition to 30 deg after opposition, except for an increase around 11 deg after opposition. Xanthe-Nilokeras showed a rather erratic behavior.

Thompson, D. T.↗
NASA NTRS1972

Brief history of the Martian 'violet haze' problem.

A brief but thorough survey of the literature on the Martian 'violet haze' problem is presented. It is evident that both the normal lack of contrast of the surface features in violet light and their occasional appearance are phenomena intrinsic to Mars. Models involving simple uniform layers of scattering or absorbing materials are inadequate to account for the observations. We suggest that the role of haze has historically been misinterpreted. The blank disk of Mars in violet light occurs when the atmosphere is relatively free of haze. The formation of optically thin white hazes over the bright areas increases the contrast and produces 'blue clearing.'

Thompson, D. T.↗
NASA NTRS1972

A new look at the Martian 'violet haze' problem. I - Syrtis Major-Arabia, 1969.

Photographic and photoelectric data obtained in 1969 have been combined to provide a relatively accurate and complete description of the so-called blue clearing phenomenon on Mars. The dark feature Syrtis Major and its surroundings are the subject of the present study. A series of comparison images of Mars in blue light was assembled to form a scale of blue clearing. The scale steps represent about the smallest readily recognizable difference in apparent contrast. The relationship between the scale number and the brightness of Syrtis Major as compared to its surroundings has been established microphotometrically. International Planetary Patrol Program photographs in blue light having Syrtis Major near the center of the disk were compared to the scale and assigned a value. The results indicate that the blue clearing of Syrtis Major was strongly dependent upon phase angle in 1969, reaching a maximum at opposition. Syrtis Major displayed a diurnal variation of blue clearing near opposition. This variation disappeared away from opposition.

Boyce, P. B.↗