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This article presents information on the study of distant comets in 1990. To capture comets in their unadulterated state, David Jewitt of the University of Hawaii at Manoa and others are looking far beyond Earth to regions where iceballs could exist free from the threat of solar melting and Jupiter's gravitational influence. Several of the new surveys will involve not just groundbased observations but also the careful tracking of two National Aeronautics and Space Administration spacecraft about to hurtle through the proposed Kuiper belt -- a region lying just beyond Neptune's orbit and believed to contain as many as 100 million comets. Another comet-hunting team relies on high-quality photographic plates at the Great Britain Schmidt telescope at Siding Springs Observatory, in New South Wales, Australia. Researchers compare sequential images spanning three consecutive nights, looking for slow-moving objects that display a distant comet's telltale path, or trajectory. Another method for seeking distant comets emerged in January at the American Astronomical Society meeting in Arlington, Virginia. Developed by Charles Alcock of the Lawrence Livermore National Laboratory and his colleagues, the technique relies on a well-known phenomenon called stellar occultation: When comets of large enough size pass in front of a star, they momentarily block the starlight from astronomers' view. INSET: Visitor from the Oort cloud?.

The article reports that a malfunction--possibly a short circuit--developed in a 5-volt power supply that drives moving parts in the observatory's Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Any hope of reviving the instrument would require a repair mission to the telescope. The other three scientific instruments on Hubble remain healthy. Despite the loss of STIS, Hubble "remains a marvelous observatory and a unique facility for learning about the universe," says John Bahcall of the Institute for Advanced Study in Princeton, N.J. NASA is now considering whether it could fix STIS as part of a proposed robotic mission to repair and upgrade Hubble some 3 years from now. The agency's decision will depend on the determination of exactly what went wrong with the power supply and whether the robotic system now under study could handle the repair.

The article discusses the passing of Venus over the face of the sun for the first time in 122 years, as seen in the United States and Greece by professional and amateur skywatchers. Among the sky watchers in Nantucket, MA, was veteran astronomer Dorrit Hoffleit, former director of the island's Maria Mitchell Observatory. Cataracts now cloud Hoffleit's vision, but the transit loomed bright enough for Hoffleit to enjoy. At age 97, she was probably the oldest astronomer to view the event, yet even she was born 25 years too late to have viewed the planet's last such passage, in 1882. Astronomers in centuries past embarked on hazardous journeys around the globe to chase the transit of Venus. Observations of a transit of Venus in the 18th century provided the first evidence for an atmosphere of a planet other than Earth. Moreover, by comparing the times that Venus entered and exited the sun's disk at far-flung locations, scientists could calculate the planet's distance to the sun and thereby determine one of the era's most sought-after cosmic details: the size of the solar system. INSET: Island Astronomy.

This article discusses a photograph of Saturn taken by NASA's Cassini spacecraft. Taken from a vantage point forty degrees above the equator, the photograph captures the full breadth of Saturn's rings and the planet's shadow across them. Cassini combines views from many perspectives to indicate the ring particles' texture and density.

The article announces that after a 7-year, 3.5-billion-mile journey, the Cassini spacecraft slipped through a gap between two of the icy rings circling Saturn and became the first spacecraft to orbit the distant planet. The probe, which will tour Saturn and many of its 31 known moons for at least 4 years, has already returned stunning images of the shimmering rings and recorded the sharpest images ever taken of smog-covered Titan, Saturn's largest moon. In Cassini's snapshots, striations within the rings resemble grooves in a vinyl phonograph record. Many of the images show wavelike features that form when the gravity of a passing moon perturbs icy particles in a ring. Although most of the rings are composed of virtually pure water ice, a spectrometer on Cassini found that particles in the F ring, the sixth ring discovered, as well as those in the rings' gaps, have a small dirt component with a composition resembling that of Saturn's outlying moon, Phoebe. The similarity supports a theory in which the rings and Phoebe have a common origin.

Reports on the unveiling of photographs of the distant Universe that are the sharpest and most detailed ever recorded. Use of the Hubble Space Telescope; Role of Holland Ford in the photography; Number of galaxies detected by the telescope.

Reports on images recently released showing the surprise brightening of Comet Halley, first observed in February 1991. Focus on comet's coma; Previous decrease in size and brightness of cloud; Unknown reasons for outburst.

Reports on an image of sky near the constellation Sextans which appears to be empty but really contains numerous extremely faint and remote galaxies. How the image was taken by the European Southern Observatory's New Technology Telescope in Chile; Process that was used to obtain the image; What the image shows.

Describes photos recently released of the Crab nebula in both false-color, near-ultra-violet and ultraviolet images taken by the Astro Observatory. Details about location of high-energy areas and star formation; Photographs of more than 900 objects taken by one of the instruments; Astro's portrait of the Crab nebula, which depicts the ultraviolet glow produced as electrons rush out from the spinning neutron star at the nebula's center; Comparison of this image with one taken in the far-ultraviolet.