|(216) Kleopatra may be the strangest, most interesting main-belt asteroid. It is the largest M-class (reflectance
spectra indicating a metallic surface) asteroid that radar observations published in 2000 showed was dogbone-shaped, about 194 km long and less than 70 km wide. Nine chords observed during a 1991 occultation, when the asteroid was near a maximum of its extreme (largest amplitude of the large main-belt asteroids) light curve, showed a roughly rectangular shape that helped convince the late Steve Ostro that this was a worthy target for radar ranging with the then (in 1999) newly upgraded Arecibo radio telescope. In addition, adaptive optics
observations with the Keck telescope show that Kleopatra is orbited by two small satellites, one of which may have occulted an 8th-mag. star for two observers in northern California during an occultation by Kleopatra (then near the minimum of its light curve) that was fairly well-observed in the Pacific Northwest in October 1980. The adaptive optics observations also indicate that Kleopatra may be more of a contact binary than a dogbone; we hope that our observations might reveal which of these hypotheses is the more likely one.
During the morning of December 24th, observers in a path extending from eastern Saskatchewan (at 11:54 UT = 5:54 am CST) south across eastern Montana, central Wyoming, eastern Utah, central Arizona (at 11:58 UT = 4:58 am MST), northwestern Sonora, and central Baja California have a chance to measure Kleopatra when it will occult a 10.7-mag. (red mag. 10.2-mag.) star in Sextans that is only 1.5' southeast of a 7th-mag. Star (that should be visible in most finder telescopes, facilitating locating the target star), 8 deg. east-northeast of 2nd-mag. Alphard (alpha Hydrae), and 16 deg. almost due south of Regulus. And observers in States adjacent to the path (that is, a State or province immediately east or west of those crossed by the path, such as California, Nevada, & Idaho to the west and New Mexico, Colorado, the Dakotas, and Manitoba to the east) are also encouraged to observe for a possible short occultation by one of the satellites.
Scott Degenhardt, Paul Maley, and I plan to set up about 30 small portable telescopes across the path and its uncertainly zone to try to measure Kleopatra's outline (the asteroid will be near a maximum of its light curve, like for the 1991 occultation). Please let me or Occult Watcher (OW; http://www.hristopavlov.net/OccultWatcher/publish.htm ) know if and where you might be able to try to observe this occultation so that we can avoid duplicating your observation and best position the small remote stations to optimally fill in the gaps in coverage by fixed site observers. The star is bright enough that it should be visible with 3-inch or larger telescopes, and may be marginally detected with "mighty mini" binocular-based systems using sensitive video cameras.
For timing, or estimating how long the star is occulted, use whatever timing resources you have (such as a digital watch's stopwatch feature started with time from http://www.time.gov/ ; see http://iota.jhuapl.edu/timng920.htm for other options). The occultation is expected to last up to 23 seconds with an easily-noticed 1.6-magnitude drop; there will be no interference from light from the distant first-quarter Moon.
THE OCCULTATION PATH
The occultation path width is given as 135 km, equal to the asteroid's mean diameter, on Steve Preston's Web page giving details for this event at http://www.asteroidoccultation.com/2009_12/1224_216_18301.htm .
But the rotation of Kleopatra is known well and the radar shape model projects into a path about 164 km wide, extending almost to the dashed "1-sigma" lines on Preston's maps.
The shadow will enter the Earth's surface at 11:51 UT Dec. 24 in northern Canada, first crossing astronomically populated s.e. Manitoba (Winnipeg is in the western half of the predicted path) at 11:54 UT (5:54 pm CST). The path then crosses eastern Montana and central Wyoming at 11:55 UT (4:55 am MST). The northwestern corner of Colorado and easternmost Utah are in the path a minute later, and then northern Arizona (east of Flagstaff) has the occultation at 11:57 UT. In southern Arizona at 11:57 UT, Phoenix is in the western half of the path, and
Tucson, sitting just outside the predicted eastern limit, could have a short occultation - observations in that area will be valuable for defining well Kleopatra's eastern edge. At 11:59 UT, the shadow is at the coast of northwestern Sonora, and at 12:00 UT (5:00 am MST) it is at the Pacific coast of central Baja California.
The star is PPM 705092 = TYC 4909-00873-1, in Sextans at J2000 R.A. 10h 03m 01.2s, Dec -05 deg. 37' 50". The 7th-mag. star near it is the 7.2-mag. spectral type K5 star SAO 137315 at J2000 R.A. 10h 02m 52s, Dec. -5 deg. 55.7'. The apparent (2009.9 true of date) position of the target star is RA 10h 03m 33s, Dec -5 deg. 40.8'. Finder charts of different scales locating the target star are at Steve Preston's Web page for the event given above.
Accuweather is forecasting 50% cover of mid-level clouds in Phoenix with the temperature 43 deg. F., but this long-range forecast can certainly change. Areas farther north have clearer skies forecast (only cirrus) and colder temperatures, with the following cloud cover and temp. (F.):
Sedona, AZ: 35%, 30 deg.
Winslow, AZ: 11%, 17 deg.
Moab, UT: 22%
Regina, SK: 47%, -7 deg.
Rather than find the target star directly, it's easier to pre- point your telescope at a brighter, easy to find star with a similar declination before the occultation, then turn off your clock drive or other tracking at the right time, and let the target star drift into your field of view at the time of the occultation. Some specific examples for doing this will be given in a future message. For this event, with a 7th-mag. star so close to the target, finding it directly may not be as difficult.
WEB RESOURCES ABOUT ASTEROIDAL OCCULTATIONS
Interactive Google maps, a list of predicted times, distances from the central line, and local circumstances for hundreds of observatories in and near the path can be found on the lines for these events on Derek Breit's global site at http://www.poyntsource.com/New/Global.htm . Similar information, as well as plans for coordinating observations, is available from Occult Watcher mentioned above; it can be downloaded from
Much more information about asteroidal occultations is given at http://www.asteroidoccultation.com/observations . Please try to time the occultation with whatever means you can, such as by using the stopwatch function of a digital watch set to the time available at http://www.time.gov/ . Those with astronomical CCD's can make
timed drift scans described at http://www.asteroidoccultation.com/observations/DriftScan/Index.htm
while other simple timing methods are described at http://iota.jhuapl.edu/timng920.htm . Another good source is IOTA's free observer's manual available at http://www.poyntsource.com/IOTAmanual/Preview.htm
Early the afternoon of Dec. 24, we plan to travel to Oakland, California, to observe the great occultation of 8.5-mag. SAO 75766 = TYC 1795-00251-1 by the approximately 120-km asteroid (81) Terpsichore, the same asteroid whose occultation I observed from 4 stations in southern Maine last month. The path for that event,
as Walter Morgan has noted, passes over the southern part of the San Francisco Bay area. The long-range forecast for Tracy, east of Oakland near where we plan to try to observe, weather permitting, now calls for 60% cirrus; of course, that will likely change.