Waltzing Mathilde - clear skies forecast for most of path for this occultation just after 9h UT Sun. am, Oct. 15
We need your help to complete NEAR's measurements of the size and shape of 253 Mathilde - we can obtain some data on the half of the asteroid that NEAR couldn't image
The predicted path extends from northernmost California to n. of Salt Lake City, s. Wyoming, s. Nebr., Missouri n. of K.C. & s. of St. Louis, & Kentucky, s.w. Virginia & n.e. N. Carolina
First I give the latest updated information, some not distributed before (such as details for pre-pointing telescopes for the event), then the information with links posted about the occultation yesterday. We still need your help to complete the mapping of the C-class asteroid (253) Mathilde. As explained more below, half of Mathilde was imaged by the NEAR spacecraft in 1997, and observations of tomorrow morning's occultation could be used to improve estimates of Mathilde's volume and density. The latest (third) forecast (21h prognosis) of Environment Canada's cloud forecast for astronomy (on which Clear Sky Clock is based) looks very good for s.w. Virginia and North Carolina, and for n. Nevada/s. Idaho/n. Utah, but poor for other locations along the path. So far, the only other observers who have said they will try it are John Goss at +94 km in VA, and Dan Caton at -76 km in NC, within the 1-sigma limits but outside the predicted path. Especially I would like to hear from anyone within the predicted path, or a little outside it, who might try to observe. If I don't hear from anyone else, I'll try to set up two stations, one a little inside each limit, at about +/-28 km at sites near I-95 near Enfield (n.) and Sims (s.). But I don't want to duplicate your chord and can modify this if I hear from you. I can't send messages after this one, but will be able to receive messages up to about 6 pm (and maybe a last chance around 10:30 pm, that's uncertain), and will also at those times make a last update to the above Web site updating the coverage information for this occultation. The target star, 11.6-mag. TYC 1330-00113-1 at J2000 RA 6h 47m 39.2s, Dec +15 deg. 14' 21", is near some 9th-mag. stars about 2.5 deg. southeast of gamma Geminorum. Finder charts of different scales to locate the star, as well as a USA path map and detailed path and other information, are on S. Preston's Web site. The finder charts may be easier to view and print from this Power Point file. There are lots of faint stars, but not any brighter ones, nearby. To locate the target star, you could center your telescope on 7.7-mag. SAO 94302 at J2000 RA 5h 05m 16.6s, Dec +15 deg. 14' 23" (virtually the same Dec. as the target star) 1h 42.1m before the predicted time of the occultation for your location (which you can find in Derek Breit's station list described and linked to below, or you can estimate the time from the USA map on Steve Preston's Web site given above), then turn off the clock drive, keeping the telescope clamped (fixed pointing), and then the target star will drift into the middle of your field of view at, or very near, the time of the occultation, which should be accurate to +/-0.3 minute or so. SAO 94302 is only about 19' southeast of 4.7- mag. 11 Orionis = SAO 94290 at J2000 RA 5h 04m 34.1s, Dec +15 deg. 24' 15". Another way to pre-point your telescope is to aim it at 5.5-mag. 58 Tauri (SAO 93876) at J2000 RA 4h 20m 36.3s, Dec. +15 deg. 05' 45" in the Hyades (about half a deg. south-southeast of 3rd-mag. gamma Tauri) 2h 26.65m (time corrected for the difference between sidereal and mean solar rate) before the occultation for your location; then the target star at the time of the occultation should be 8.6' north of where 58 Tauri was (so this pre-pointing is not nearly as accurate as the one for SAO 94302). David Dunham, 2006 October 14, 16h UT Phones home 301-474-4722; office 240-228-5609; cell 301-526-5590 emails dunham@starpower.net or office david.dunham@jhuapl.edu ______________________________ Oct. 13: We need your help to complete the mapping of the C-class asteroid (253) Mathilde. You can waltz with Mathilde on Sunday am, October 15, when the 58-km asteroid will occult an 11.6-mag. star high in the sky near gamma Geminorum. On June 27, 1997, the NEAR spacecraft obtained spectacular images of half of this slow-rotating asteroid enroute to Eros. Mathilde was found to be a rubble pile with huge craters, some almost half its diameter. But only the sunlit half of Mathilde could be photographed - click here. The mass of Mathilde was determined from the small gravitational deflection of NEAR's trajectory as it sped past, but the volume remains uncertain. By obtaining points on both the (June 1997) sunlit and dark sides of Mathilde during the occultation, it may be possible to refine the volume and density of this curious asteroid. So although the star is relatively faint (but it should be observable with 8-inch or larger telescopes) and the path location uncertain (The 1-sigma error is about a full path-width), the occultation deserves a special effort. For a 500-kilobyte Power Point file with a map of the path across the USA, detailed finder charts of different scales also from Steve Preston's Web site, and weather forecast maps, click here. This has been updated this afternoon, Oct. 14, to include the 3rd (21h prognosis) weather forecast and a map showing the path in more detail across north-central North Carolina. The occultation path crosses the USA from northernmost California to Cape Hatteras, North Carolina. The occultation is expected to occur just before 9:04 UT (2:04 am PDT) at Crescent City, Calif.; then at 9:04, the path extends from Yreka, Calif. to Logan, Utah; at 9:05 UT (3:05 am MDT), across s. Wyoming (Cheyenne and Laramie) & the n.e. corner of Colo.; at 9:06 UT (4:06 am CDT), across s. Nebraska & St. Joseph, Missouri; at 9:07 UT, just north of St. Louis (which could have an occultation) to Louisville, Kentucky; at 9:08 UT (5:08 am EDT), over e. Kentucky, s.w. Virginia, and n.-central N. Carolina; and at 9:900 UT, over eastern North Carolina. Considering the errors, an occultation could occur as far south as Salt Lake City; Boulder, Colo.; Kansas City, MO; & Fayetteville, NC; or as far north as Boise, ID; Omaha, NE; Bloomington, IN; Covington, KY; and Roanoke and Chesapeake, VA. A central occultation is expected to last 6.1 seconds with a 3.5-mag. drop. Let us know your plans to observe this important event so that mobile observers can select locations to avoid duplicating your observation. If you are mobile, let me know that so I can suggest a location that would be most useful for the overall coverage. A first station list will be distributed about noon Saturday giving committments that I've learned up to then. Very detailed maps for this, and other asteroidal occ'n events listed below, 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. For Sunday evening's Dynamene occultation, for all locations in the path in the USA and s. Canada, the altitude will be over 40 deg. above the southern horizon in a dark sky). The list 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. I have to work at a STEREO mission launch rehearsal Sat. evening, Oct. 14. My role in that should be over by about 10:30 pm, so I plan to drive directly from the STEREO control center in Laurel, MD to the occultation path near Rocky Mount, NC. I had time to set up two stations near both predicted limits of the occultation. If others would be interested in joining this expedition, let me know. _____________________________________ David Dunham, 2006 Oct. 13, 6 pm EDT (22h UT) Phones home 301-474-4722; office 240-228-5609; cell 301-526-5590 e-mail david.dunham@jhuapl.edu home e-mail: dunham@starpower.net .