Comet Hyakutake Passes the Earth

Astronomy Picture of the Day

This picture of Comet Hyakutake taken the night of March 21/22 in Illinois, USA shows the enormous tail that has already developed. The silhouette on the right is a foreground tree, and the superposed green circle on the left shows the size of the full moon. Today Comet Hyakutake makes its closest approach to the Earth. As the comet moves into the inner Solar System, it will pass the Earth at about 40 times the distance of our Moon. This is not the closest a comet has ever come, though. As recently as 1983 Comet IRAS-Araki-Alcock came three times closer than Hyakutake, and in 1770 Comet Lexell got yet twice closer than that! Asteroids - usually less massive than comets - frequently whiz by inside the Moon's orbit, with four doing so far in this decade. In the distant past, asteroids have even struck the Earth. Comet Hyakutake is much brighter now than Comet IRAS-Araki-Alcock ever got, and in fact is the brightest since Comet West in 1976. Comet Hyakutake will be easily visible all week. Latest Comet Hyakutake images: JPL, Crni Vrh Observatory, Slovenia, Fayetteville Observer-Times, NASA's Night of the Comet

By Peter McCullough (U. Illinois Urbana-Champaign) McCollough's MPEG Movie of Comet Hyakutake taken March 23

Venus' South Polar Vortex

Astronomy Picture of the Day

What's happening over the South Pole of Venus? To find out, scientists have been studying images taken by the robotic Venus Express spacecraft when it passes over the lower spin axis of Earth's overheated twin. Surprisingly, recent images from Venus Express do not confirm previous sightings of a double storm system there, but rather found a single unusual swirling cloud vortex. In the above recently released image sequence taken in infrared light and digitally compressed, darker areas correspond to higher temperatures and hence lower regions of Venus' atmosphere. Also illuminating are recently released movies, which show similarities between Venus' southern vortex and the vortex that swirls over the South Pole of Saturn. Understanding the peculiar dynamics of why, at times, two eddies appear, while at other times a single peculiar eddy appears, may give insight into how hurricanes evolve on Earth, and remain a topic of research for some time. In three months, the European Venus Express spacecraft will be joined around Venus by the Japanese Akatsuki satellite.

Expansive Comet Holmes

Astronomy Picture of the Day

The spherical coma of Comet Holmes has swollen to a diameter of over 1.4 million kilometers, making the tenuous, dusty cloud even bigger than the Sun. Scattering sunlight, all that dust and gas came from the comet's remarkably active nucleus, whose diameter before the late October outburst was estimated to be a mere 3.4 kilometers. In this sharp image, recorded on November 14 with the Canada-France-Hawaii Telescope, stars are easily visible right through the outer coma, while the nucleus is buried inside the condensed, bright region. The bright region of the coma seems offset from the center, consistent with the idea that a large fragment drifted away from the nucleus and disintegrated, producing the comet's spectacular outburst. Of course, more recent images of Holmes also show the bright star Mirfak (Alpha Persei) shining through as the comet sweeps slowly through the constellation Perseus.

By Jean-Charles Cuillandre

Sprint the Flying Space Camera

Astronomy Picture of the Day

Yes, but can your soccer ball do this? The ball near the middle of the above photograph is actually a robotic camera designed to float about a Space Shuttle and the International Space Station and take pictures. Named "Sprint", it is NASA's first Autonomous Extravehicular Activity Robotic Camera (AERCam) and was tested earlier this month by the crew of Space Shuttle Columbia. Sprint's diameter is actually about 50 percent larger than a soccer ball, and astronauts make a goal of not kicking it.