[Prev][Next][Index][Thread]

(meteorobs) The Moon's "Leonid" Tail

Forwarded from Sky & Tel......


===========================================================================
             SKY & TELESCOPE'S NEWS BULLETIN - JUNE 11, 1999
===========================================================================

THE MOON'S "LEONID" TAIL

During an observing run last November, astronomer Steven M. Smith (Boston
University) kept seeing a bright smudge in the images from his all-sky CCD
system. At first he thought dew on the camera lens was to blame. But he and
three colleagues later realized that they had serendipitously discovered a
comet-like tail of sodium atoms blasted off the Moon during the Leonid
meteor shower.

Astronomers have known since the Apollo era that our Moon has a very
tenuous atmosphere created by the micrometeoroids that continuously rain
onto the lunar surface. Although totaling only about 50,000 atoms per cubic
centimeter, the lunar "air" contains traces of neutral sodium atoms that
are detectable from Earth thanks to their strong, yellow "D-line" emissions
at 5890 and 5896 angstroms. 

As team member Jody K. Wilson explains, last November's Leonid meteor
shower caused a brief but dramatic increase in the amount of escaping
sodium vapor, which was pushed away from the Moon and into a
million-kilometer-long tail by the radiation pressure of sunlight. By
chance new Moon occurred during the Leonids' peak, causing the lunar sodium
tail to sweep over and past Earth two days later. Smith's camera, equipped
with a sodium filter, just happened to be looking "down the tail" in the
anti-Sun direction at that time. "We were very lucky," he admits. The teams
results were presented June 1st at a meeting of the American Geophysical
Union in Boston.

The Moon will be near first quarter for this year's Leonids, so the
Sun-Moon-Earth geometry will prevent a repeat performance. But the Boston
University team plans to be looking anyway. "The moral is that you should
look all the time," notes Jeffrey Baumgardner. "You never know what will
turn up." 



To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html