Kari Lumme

Photometry of Saturn’s Rings

A total of 202 photographic plates of Saturn taken from four different locations and in seven different colors have been studied in order to define better the variation in ring brightness with solar phase angle, declination of the earth with respect to the ring plane, orbital phase angle of the ring particles, and wavelength. A major effort has been made to investigate possible differences in the photometric behavior of the A and B rings.

Saturn's Rings: Azimuthal variations, phase curves, and radial profiles in four colors

Abstract Four-color photographic photometry of Saturn for the 1977–1979 apparitions has been analyzed to determine the dependence of ring brightness on wavelength, solar phase angle, ring particle orbital phase angle (azimuthal effect), declination of the Earth relative to the ring plane (tilt angle), and radial distance from Saturn. Azimuthal brightness variations up to ±20% relative to the ansae are clearly apparent for the maximum of ring A, but are not detectable for ring B or the outer portion of ring A. The shape of the intensity ( I ) versus orbital phase angle (θ) curve varies with ring tilt ( B ) and probably with wavelength, and shows 180° symmetry. As characterized by its slope near the ansae, this curve suggests that the azimuthal effect increases as B decreases from 26 to ≈11°. The phase curves l ( α ) for the ansae show very little dependence on ring tilt (26° > B > 6°), on wavelength, or on radial distance from Saturn; possibly the curves are somewhat steeper at the smallest tilt angles and for ring A relative to ring B. The radial profile of both rings becomes flatter with decreasing tilt angle and with decreasing wavelength. The latter effect is a natural result of the classical, many-particle-thick ring model.

Azimuthal brightness variations of Saturn's rings

Saturns ring A exhibits a variation in brightness with azimuth (with orbital phase of the ring particles). Maximum brightness occurs at about theta=45

The tilt effect for Saturn's rings

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Azimuthal brightness variations of Saturn's rings. II - Observations at an intermediate tilt angle

and theta=225

Theoretical interpretation of the ground-based photometry of Saturn's B ring

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International Planetary Patrol observations of Saturn's rings. II. Four color phase curves and their analysis

and minimum brightness at about 135

Azimuthal brightness variations of Saturn's rings. III - Observations at tilt angle B approximately equal to 11.5 deg

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Five-color photometry of Saturn and its rings

and 315

On the surface brightness and geometric albedo of some Martian areas

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