It's not too early to start reobserving Jupiter. The giant planet dipped into the Sun's glare a few months ago, but you can now spot it before dawn low in the southeast. Atmospheric seeing may be a problem that close to the horizon, but can you see any trace of the atmospheric scars left last July by pieces of Comet Shoemaker-Levy 9?
Last week two record-breaking asteroid discoveries were made, and here are more details. One object, as big as the Empire State Building, appears to circle the Sun more quickly than any known body except the planet Mercury. It was found by keen-eyed observer Robert H. McNaught on a Schmidt plate taken December 6th at Siding Spring, Australia. After an urgent appeal for follow-up observations, Californian John E. Rogers obliged on the 9th with his 10-inch Meade Schmidt-Cassegrain and ST-6 CCD camera. From Rogers's five measurements plus those supplied by McNaught, Gareth Williams calculated that this object, designated 1994 XL1, is a rare Aten-type asteroid that orbits the Sun in less than a year. In fact, it goes around in just 6 1/2 months -- outracing not only Earth but Venus as well. With a mean distance of 0.67 astronomical unit (100 million km) from the Sun, 1994 XL1 might never have been spotted. But it has a highly eccentric orbit with an inclination of 28 degrees, and on the night of discovery it was near aphelion just outside the Earth's orbit. The asteroid is perhaps 300 meters across.
The other new object, the size of a small house, whizzed by Earth on December 9th at 19:30 Universal Time, missing our planet's surface by a scant 100,000 km. The first warning of its existence had come just 14 hours earlier when Jim Scotti, using the Spacewatch telescope in Arizona, found a 17th-magnitude speck streaking northwest through the constellations Cetus and Aries. Amazingly, some 40 or 50 objects of similar size probably pass within the Moon's distance every day, but current search programs only rarely discover them. 1994 XM1 breaks the previous near-miss record of 160,000 km set by 1994 ES1 last March. It is 6 to 13 meters across, judging by its brightness; if a stony object this size collided with Earth, it would break up in the atmosphere long before reaching the ground.
It's not too late to catch a bit of the annual Geminid meteor shower, which peaked on the night of December 14th. Typically this stream shows off at least one meteor per minute to observers under dark-sky conditions, though the Moon has been a definite problem this year.
Strong moonlight continues to flood the night sky this week, with full Moon occurring early on Sunday, December 18th, at 2:17 Universal Time (Saturday night for those in North America).
New Jersey observer Rick Krezewcki wants you to know that naked-eye sunspots are now making their way across the Sun's disk. Always use proper filters and procedures when viewing the Sun to avoid injury.