Good Occultation of 8.7-mag. SAO 117582 by large asteroid Nemausa over Calif. (& Colombia to Alaska) Tues. pm, Feb. 27/28
Prediction and pre-event plans two days before the event, as of 2007 Feb. 26
8.7-mag. SAO 117582, about 7 deg. east of Hydra's head, will be occulted by the 140-km C-class asteroid (51) Nemausa over most of California, as well as the s.w. corners of Ariz. & Oregon; w. Sonora; and parts of Alaska, Colombia, & s.w. Mexico tomorrow night, Tues. Feb. 27/28 (actually early Wed. am Feb. 28 in most places). The first Astro Meteo forecast (a little different from Accuweather) and current observer plans are below; we need help to cover the wide path since the current coverage is poor and likely to be reduced by bad weather. The path covers most of California, but Los Angeles is just southwest of the 1-sigma s. limit and the S.F. Bay area is farther from it (Sacramento & Fresno are on the predicted s. limit). The path misses s. Baja Calif., but passes over much of Sonora, including Hermosillo; Yuma, Ariz. is in the path, too. The path also passes over s. Colombia at 8:35 UT; the time at Pt. Barrow, AK is 8:51 UT. We need your help to observe this very good occultation of 8.7-mag. SAO 117582 by the large (148 km) C-class ("carbonaceous" spectral characteristics) asteroid (51) Nemausa visible late Tuesday night (just after midnight, so actually Wed. am) from western Sonora, the s.w. corner of Arizona, most of California, and the s.w. corner of Oregon. The path also extends over parts of Alaska and Colombia. The occultation will occur just before 8:42 UT Feb. 28 UT (1:42 am MST) in Hermosillo and just before 8:43 UT in Yuma, Arizona. The path sweeps over s. Calif. at 8:43 UT (12:43 am PST) and n. Calif. at 8:44; and over s.w. Oregon at 8:45 UT. Please let us know your plans to try to observe this occultation so that we can best place mobile observers to avoid your line. The occultation will last up to 16 seconds with an easily-seen 1.8- magnitude drop; the 80% Moon will be only 24 deg. away southeast of Pollux. The star, also known as HIP 45653, is at J2000 RA 9h 18m 20.9s, Dec +7 deg. 04' 24", in the s.e. corner of Cancer about 9 deg. south and a little west of Saturn, and 7 deg. east and a little north of Hydra's head. A distinctive pair of 7.5-mag. stars, about 3' apart in almost the north-south direction, is 20' west-northwest of the target star. Finder charts of different scales are on Steve Preston's Web page. Updated path maps & data are also on Steve Preston's Web site above. Very detailed maps (google maps column) are on Derek Breit's interactive Web page that links to the very detailed maps and satellite imagery of maps.google.com with overlays of the occultation paths. Also on Breit's Web site are station lists giving local circumstances, for many observer stations. It gives the predicted time of the event, distance from the updated central line, probability that an occultation will occur there, and altitudes of the star and the Sun. If your station is not in that list, please let me and Derek, breit_ideas@hotmail.com , know so that you can be added to future lists. Also included there now are lists of stars with offset times and declination differences for pre-pointing telescopes for these events. The Canadian weather forecast for astronomy (Astro Meteo) is forecasting virtually overcast skies, with some rain and snow, over northern California south to Tehachapi, with some clear sky in the western San Joaquin Valley but outside the predicted path. The Astro Meteo map also shows solid clouds from Torrance to Apple Valley and south along the coastal mountains to the Mexican border, and west of that line to the coast; a fair amount of clouds are also shown along I-10 from Indio to Blythe. There's a large clear area extending approximately for Ojai over much of the San Gabriel Mtns., over the Antelope Valley, then northward bounded on the west by the Sierras extending across most of the high part of the Mojave Desert across southern Nevada, and a smaller clear area along I-8 from El Centro to Yuma and east into s.w. Arizona. However, they predict strong winds centered around Barstow - Baker, so I-15 will be a poor place to try to observe. Moderate winds are forecast for the Antelope Valley, with relatively light winds north of there, in the area east of the Sierras. This is the 44h/45h prognosis, the first one available; the next one will be available about 4h UT Feb. 27 (tonight), but if I go to California to observe this event myself, I won't be able to update this Web site again, but you can go to the Astro Meteo Web site to get the later forecast maps yourself. I've placed the 44h and 45h (8h & 9h UT of Feb. 28) prognosis charts in this Power Point file, including cloud cover, transparency, and wind. Only a few observers have so far indicated that they will try this outstanding event; I hope that several more will try it. Especially valuable will be observations from Hermosillo (just inside the predicted northern limit) and the Riverside area (just inside the southern limit). The predicted southern limit passes over Lancaster, Ontario, w. Riverside, Murrieta, w. of Julian, and Jacumba, but the 1-sigma southern limit, where an occultation could well occur, passes over West Covina and Yorba Linda. Of course, there could be a larger shift so observers throughout California are encouraged to observe, but those near the coast can increase their chances considerably, and provide much-needed coverage across the path, if they can travel east into the desert. This asteroidal occultation is one of the best of the year in California. Too bad more observers can't get away to try it where the weather may be good. Some of you have already responded, but I forgot to say last night: So far, coverage of the path is poor, with the following attempts known, all except the first in Calif.: +66 Antonio Sanchez, Salvador Aquirre, Hermosillo, Sonora +17 Derek Breit, Emigrant Gap -15 Chuck Jopson, Etna -38 Lewis Center, Apple Valley, CA -52 Bob Jones, Running Springs -104 Greg Lyzenga, Claremont -152 Dave Werner, Seal Beach Ernie Iverson may be mobile for the event, but can't get to the low desert, only a little inside the s. limit, probably in the Antelope Valley. Unfortunately, the weather forecast is very poor for the first three, and quite iffy for the other 4 "fixed sites". If I proceed with my plans, I will set up at least two stations in the northern half of the path mainly along Route 178 between Johannesburg and Route 190, south and north of Trona - so far, I would only need to avoid Derek's plan, although he has little chance. [But with the updated weather forecast, I observed instead from the low desert, from sites near I-10 east if Indio; click here for more]. David Dunham, 2007 Feb. 26, 18h UT home dunham@starpower.net 301-474-4722 cell 301-526-5590 office & Blackberry david.dunham@jhuapl.edu 240-228-5609