Press Release: Lunar Impacts Confirmed during Leonid Meteor Storm

North American astronomers recorded at least six Leonid meteors strike the Moon's surface late Wednesday night, November 17/18, 1999. It was part of a meteor storm that had swept over Europe, Africa, and the Middle East a few hours earlier. Each of these meteors produced a flash of light that was seen with a video camera or the eye by at least two independent observers, marking the first confirmed observations of lunar meteor impacts. The observations were orchestrated by Dr. David Dunham, president of the International Occultation Timing Association (IOTA, Greenbelt, MD), an organization primarily of amateur astronomers who record eclipses of stars by the Moon and by asteroids. Such eclipses are called "occultations" by astronomers after "occult", a Latin word meaning to cover. When Dunham read a NASA Web site suggesting that meteors might be seen hitting the Moon during the Leonid meteor shower predicted to occur on November 17/18, he used the Internet to encourage IOTA observers to use their equipment to monitor the dark side of the Moon that night.

Brian Cudnik, a reseach technician at Prairie View Agricultural and Mechanical University at Prairie View and at Rice University in Houston, Texas, watched visually with a 35cm (14inch) telescope. At about 10:46:20 pm Central Standard Time (4:46:20 am Greenwich Mean Time, or GMT, of November 18th), he saw a very brief orange flash near the center of the Moon's dark side and estimated that it was about half the brightness of the North Star, or "3rd magnitude" in astronomical terms*. Cudnik sent a message to Dunham reporting the observation and asking for confirmation. Dunham then looked at his own video record obtained that night with a 13cm (5inch) telescope set up at fellow observer George Varros' home in dark rural country near Mount Airy, Maryland, about 40 miles northwest of Washington, DC. He was amazed to see the flash, as Cudnik described it, in his black-and-white recording, and was able to refine the time to 4:46:15.2 am GMT (11:46:15.2 pm Eastern Standard Time). When word of this confirmed sighting spread, Steven Hendrix reported that he also saw a flash on the dark side of the Moon at about that time using an 11cm (4inch) telescope at Cameron, Missouri, but he did not time it.

Then Pedro Valdes Sada, Universidad de Monterrey, Monterrey, Mexico, and David Palmer, Goddard Space Flight Center, Greenbelt, Maryland, examined their video tapes, made with black-and-white cameras attached to 20cm (8inch) and 13cm (5inch) telescopes, respectively. Neither was pointed at the right part of the Moon at 4:46:15.2 am GMT to confirm Cudnik's flash, but each of them found two more flashes and reported their approximate times and descriptions to Dunham. Dunham found each of these four new flashes in his recording. Sada also found the first of Palmer's flashes on his videotape, as did Rick Frankenberger in San Antonio, Texas, providing a quadruple confirmation of that event. In the table below, the distances from large lunar craters are given. All of the impacts were just north of the lunar equator in the western part of Oceanus Procellarum (Ocean of Storms, although it is an "ocean" of frozen lava rather than of water) except the second and third ones, which occurred in highlands southwest of Oceanus Procellarum. Each of the impacts was bright on only one video image, and was seen at a considerably fainter level on the next image 1/60th second later. Don Stockbauer, Victoria, Texas, determined most of the times in the table from a copy of Dunham's tape using a special video time inserter designed by Peter Manly of Sun City, Arizona. Manly's device senses the minute tones of the short-wave time signal station WWV that was recorded in the audio part of the tape to trigger an accurate display of the time. The lunar location describes where the impacts occurred relative to large known craters.

Lunar Impact Information Measured from D. Dunham's Video Tape

Discoverer	GMT (Nov. 18)	Magnitude	Approximate Lunar Location
D. Palmer	3:05:44.2 am	5	50 km east of Harding
D. Palmer	3:49:40.4 am	3	on west wall of Hevelius
D. Palmer	4:08:04.1 am	5	120 km southwest of Rocca
B. Cudnik	4:46:15.2 am	3	50 km east-northeast of Cardanus
P. Sada	5:14:12.9 am	7	200 km west-northwest of Marius
P. Sada	5:15:20.2 am	4	75 km south of Schiaparelli

The Leonid meteors, named for the fact that they appear to come from the direction of the constellation Leo in our sky, are debris ejected from the large Comet Tempel-Tuttle each time it passes near the Earth's orbit almost exactly three times each century. The debris particles move in streams through space that are nudged slightly in different ways that depend on the locations of the larger planets at the time they are ejected. Dr. David Asher at Armagh Observatory, Armagh, Northern Ireland, developed a computer model to calculate these complex motions. He successfully predicted that this year's Leonid storm would be visible only from the longitudes of Europe around 2:08 am GMT of November 18 when the Earth passed close to the Leonid stream that was ejected from Comet Tempel-Tuttle in 1899. At the time, the Moon was two days past last quarter phase, travelling behind the Earth in its orbit about the Sun and slightly farther from the Sun than the Earth. Asher used his computer model to calculate that the Moon passed closer to the center of the 1899 Leonid stream than the Earth and almost three hours later, around 4:49 am GMT, very close to the times of the observed impacts. The model indicated that the intensity at the Moon this year must have been similar to the super Leonid storm, also from the 1899 stream, that struck the Earth in 1966. Bill Cooke, Marshall Space Flight Center, Huntsville, Alabama, had predicted this last September.

Jay Melosh, at the University of Arizona's Lunar and Planetary Laboratory, calculates that the mass of the impacting meteoroids ranged from several tens of kilograms to a few hundred kilograms (hundreds of pounds) and that they were about half a meter (or one to two feet) in diameter. The resulting craters are probably 10 to 15 meters (30 to 50 feet) in diameter. However, such large bodies in the Leonid meteor streams are thought to be significantly rarer than the new lunar observations imply. Mark Matney, of Lockheed Martin Space Operations in the Orbital Debris Program Office at NASA Johnson Space Flight Center notes that much more energy was converted into light than expected from standard theories during artificial satellite collision tests. Matney believes that hypervelocity collisions may produce some non-equilibrium phenomena that produced the extra light. So the meteoroids causing the observed lunar impacts may be ten to a hundred times smaller than Melosh indicates, making them more compatible with the expected Leonid stream distribution. Although certainly not visible from the Earth, the new craters might be found by comparing new images that will be obtained by the Japanese Selene spacecraft, scheduled for launch in 2003, with Apollo or Lunar Orbiter photoes taken about thirty years ago.

The Leonids and other dense meteor streams are of interest to NASA and other space agencies since they pose some threat to space navigation. Dunham and other astronomers plan to examine their tapes, and those made by a few other observers, more thoroughly. Several more impacts, mostly fainter ones, will probably be confirmed. For example, Roger Venable tried to videorecord the Moon's dark side with his 41cm (16inch) telescope near Wrens, Georgia, but glare from the sunlit part of the Moon spoiled that effort. He had a much better view watching visually, starting at 2:15 am GMT (9:15 pm EST). He saw dozens of faint flashes, coming in groups at 10th to 12th magnitude, but he became exhausted by the intense observation and stopped watching at 2:57 GMT. This was similar to video observations made by Laurent Pellerin, Seminole Community College Planetarium, with the 66cm (26inch) telescope at the University of Central Florida's Robinson Observatory the previous night, November 16/17. He recorded several flashes, but unfortunately a technical problem prevented accurate timing of the tape. Nevertheless, Dunham and a few other IOTA observers recorded that night as well, so some of the brighter flashes may appear in the timed videos made with their smaller telescopes. Pellerin was unable to use the Robinson Observatory telescope on November 17/18.

These successful observations with small telescopes will certainly encourage lunar observations during future meteor showers. For example, the lunar geometry (Moon 2 days before first quarter) will be favorable for this year's annual Geminid meteor shower that will occur around December 13.

For images and more information, see http://iota.jhuapl.edu and IOTA's Web site at http://www.lunar-occultations.com/iota NASA lunar Leonids Web site: http://www.spacescience.com/newhome/headlines/ast03nov99_1.htm Armagh Observatory Leonid prediction site: http://www.arm.ac.uk/leonid

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*The brightest stars in the sky are 1st magnitude while those just barely visible to the naked eye during a clear, dark night are 6th magnitude.

Questions should be addressed to David Dunham, e-mail david.dunham@jhuapl.edu or telephone 1-240-228-5609, home 1-301-474- 4722. At his job at the Johns Hopkins University's Applied Physics Laboratory in Laurel, MD, Dr. Dunham calculates spacecraft orbits and maneuvers, primarily for the Near Earth Asteroid Rendezvous mission - see http://near.jhuapl.edu for more information.

Contact information for others listed above:

Brian Cudnik, cudnik@cps.pvsci.pvamu.edu, phone via 1-713-527-4939

Steven Hendrix, SteveH8835@aol.com

Pedro Valdez Sada, psada@ix.netcom.com, phone via 1-210-545-4688

Rick Frankenberger, rickf@stic.net, phone 1-512-681-2276

David Palmer, David.M.Palmer.1@gsfc.nasa.gov, phone 1-301-286-2739

George Varros, gvarros@clark.net, phone 1-301-831-5605

Don Stockbauer, donstockbauer@lycosmail.com

Peter Manly, petmanly@bix.com

David Asher, dja@star.arm.ac.uk

Jay Melosh, jmelosh@lpl.arizona.edu, phone 1-520-621-2806

Mark Matney, mark.matney1@jsc.nasa.gov, phone 1-281-483-2258

Laurent Pellerin, PelleriL@mail.seminole.cc.fl.us, phone 1-407-328-2409

Roger Venable, rjvmd@knology.net, phone 1-404-736-1740



1999 December 8