Asteroidal Occultations (Eclipses of Stars by Asteroids)
Help us measure the sizes and shapes of asteroids by timing their eclipses, or occultations, of stars
Binoculars occultation of 5.7-mag. SAO 94227 by the large asteroid (45) Eugenia and its moons in n. Mexico and s. U.S.A. Sat. pm, March 8
General information on how you can find the next asteroidal occultations near YOUR location is given
Updated: 2008 March 1, 5:30 UT
Please help us measure asteroids by observing their occultations. The spectacular occultations by Eugenia and its moons noted above are described extensively here. Other occultations through early April visible in the Mid-Atlantic States are described here. Some asteroidal occultations were observed in Maryland during February as described here. Accounts of six previous asteroidal occultations observed in late 2007 are given below: (187) Lamberta on Dec. 20 (219) Thusnelda on Dec. 18 (903) Nealley on Nov. 19 (585) Bilkis on Nov. 11 (15) Eunomia on Nov. 10 More about these and other previously-observed occultations is/will be posted on Brad Timerson's N. American asteroidal occ'n results page. BEST EVENT WORLDWIDE PREDICTIONS FOR 2007 AND 2008 Steve Preston has set up Web pages with details of the best asteroidal occultations of 2007 and 2008. Included are events with stars brighter than mag. 10.7 in astronomically populated areas (brighter in less astronomically populated regions) and with at least a 95% chance for an occultation (formal prediction uncertainty) for an observer on the predicted central line. Steve has also created a .csv file (that can be used with Excel and most other spread sheet programs) of over 2000 events during 2008, including all of Edwin Goffin's events and many more of mag. 10.5 and brighter found by Scott Donnell. I have edited down Steve's spread sheet to form this Excel file of what I consider the best 140 asteroidal occultations of 2008. The Excel file includes links to the detailed predictions on Steve Preston's Web site for each event. The list includes all of Steve's A and B priority events, and most of his C events, as well as other occultations of bright stars with reasonably good statistics. Much information about observing occultations of all types is in "Chasing the Shadow: The IOTA Occultation Observer's Manual" available for free here. Much information about asteroidal occultations in general is on Brad Timerson's asteroidal occultation page, with info. about reporting observations, etc. _____________________________________________________ North American observers are encouraged to find updated asteroidal occultation paths near them by consulting the maps and associated tables on Derek Breit's N. American paths Web page. He also has similar maps for Australia here. And now he has these maps for S. America and also Europe. Once a path of interest is identified, you can then get details of the event, including finder charts of different scales to locate the target star on Steve Preston's Web site - scroll down the table to the line with the date and event you want, and click on the item in the right-hand column for the page for the event that links to the regional map, finder charts, and other information. Those outside North America can find some similar information for their areas on the regional asteroidal occultation Web sites listed in (and linked to from) the section, "Links providing possible additional information" in the quarterly asteroidal occultation prediction page of Rob Robinson's main IOTA Web site. You can also just scroll down the list on Steve Preston's Web site which tells the general region of each event, to find events that might be of interest to you. In addition, IOTA members should have a plain text table of events for the year that tells the distances from their location and the circumstances for most predicted asteroidal occultations and appulses computed for their location, the "local circumstances" file with a name like xlcm06.### where "x" is the letter of your IOTA region and ### is your station number in that region. Similar tables can be generated with the WinOccult program that can be obtained from the main IOTA Web site. Also useful is Sander Pool's Web site that lets you input coordinates of your observing location and then it will list all upcoming asteroidal occultations from Steve Preston's site that will occur within a specified distance of your location. This has an advantage over Occult Watcher, described below, in that Sander Pool's site includes all events through the end of 2008 while Occult Watcher only has events in the current detailed update cycle, generally for the next five weeks. Even better than Sander Pool's site is new software called Occult Watcher that I recommend that you install on your computer. With it, you input your position and it searches Steve Preston's predition Web site, informing you of all asteroidal occultations in your region during the next 4-5 weeks, giving probabilities and other details. Whenever a path is updated, the software lets you know. It also has provision for you to specify your observing intentions, and these are displayed along with those of other observers to help plan the overall coverage for the event. Hristo Pavlov in Sydney, Australia wrote this program; you can get it here. He recently updated the program, as explained on his Web site. For all 2007 "Preston" events worldwide, very detailed maps 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 and their 1-sigma uncertainty zones. Also on that Web site are station lists giving local circumstances, for many observer stations, now including all of the MPC observatories and other sites in an expanded list of 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 on this site are lists of stars, mostly brighter than the target star, that can be used before the event to pre-point stationary (non-tracking) telescopes. Note that the path predictions are not perfect, they can shift due to mainly now to stellar proper motion errors that are increasing with time from the 1991 mean epoch of the Hipparcos satellite observations. So observers not just within the predicted path, but also north and south of it, at least within the 1-sigma uncertainty zones shown by the dashed lines on the maps on Steve Preston's Web site, should also watch for, and preferably be prepared to record and/or time, an occultation. Sometimes (less often, but not impossible) shifts of 2-sigma can and do occur, so observers a little outside the 1-sigma lines are also encouraged to observe. Theoretically, the actual path will be within the 1-sigma lines 67% of the time, and within the 2-sigma lines 95% of the time. ________________________________________________ David Dunham, 2008 March 1, 12:30 am EST Phones home 301-474-4722; office 240-228-5609 (usually only Tues. and Wed.); cell 301-526-5590; office e-mail david.dunham@kinetx.com with Blackberry for mobile use home e-mail: dunham@starpower.net .