April 19, 2006T
he Lyrid meteor shower reaches its peak Saturday morning in a moonless sky great circumstances for watching the shower's faint, fleeting meteor trails. The waning crescent Moon stays below the horizon until about 3 a.m.
for observers at mid-northern latitudes. This gives skywatchers several hours of dark sky late Friday and early Saturday in which to enjoy the show.
This year, though, moonrise brings an opportunity to witness something unusual. Those with a modest telescope and a lot of patience may witness point flashes from Lyrid meteoroids striking the lunar surface.
"Lunar impacts are petty rare events," says Brian Cudnik, who coordinates amateur observations of lunar impacts for the Association of Lunar and Planetary Observers
. As many as a dozen members may be watching the Moon for impacts during any observing opportunity, he says. "There are between 5 and 8 favorable alignments each year" in which the Moon's unilluminated side grazes a stream of meteoroids. "Most of the time it's an evening event, involving a waxing crescent, but in this case it happens in the morning with a waning crescent," he explains.
Lyrid particles, which are shed by Comet Thatcher (C/1861 G1), collide with Earth or Moon at a brisk 108,000 mph (173,800 km/h). Meteors are brief glowing trails produced as comet material burns up in Earth's atmosphere. The same particles can strike the Moon's surface, creating a brief pinpoint flash as bright as magnitude 7 easily within the range of small scopes.
"The Lyrid shower is rather weak, so the chances of seeing a lunar impact are slim, but there's always that chance," Cudnik says. Impacts have been reported during the Leonid, Perseid, and Taurid showers. Low-light-level video cameras offer the best way to identify a hit, but determined visual observers can see lunar strikes, too.