Mid-Atlantic Asteroidal Occultations Tonight - New 2013 Aug. 1
The best will be an occultation of an 11.3-mag. star in northern Sagittarius by the asteroid (585) Bilkis at 3:14am EDT
A difficult occultation of a 13.2-mag. star near M11 by the asteroid (136) Austria will occur at 2:30am, 44 min. before the Bilkis event for those with large scopes.
It will probably be rather cloudy the next night (Friday night, August 2/3) for an occultation of a 9.5-mag. star by a small asteroid that has only about a 10% chance of occurring for an observer in our region.
For non-astronomers, "occultation" is a term that astronomers use for an eclipse of a star by an asteroid or by the Moon. Click here for information about tonight's good lunar grazing occultation of 6.2-mag. ZC 798 in the Richmond area (it's also visible farther to the southwest, to Texas, in a very narrow path) and click here for information about other events in the Mid-Atlantic region up to mid- September. _______________________________________________ A summary of the two events tonight, and the one tomorrow, is in the list below. 2013 dur. Ap. Date Day EDT Star Mag. Asteroid dmag s " Location Aug 2 Fri 2:30 2UC29708788 12.8C Austria 0.4 6 10 w&nVA,sMD;DC? Aug 2 Fri 3:14 TYC57150408 11.3 Bilkis 3.1 6 7 DE,sMD,VA;DC? Aug 3 Sat 0:40 SAO 185777 9.5 Viipuri 6.9 6 4 VA,TN;DC,MD? Aug. 2, Bilkis: I'll discuss this, the best of the events first, since most won't be interested in the oher ones. This event 44 min. after the Austria event is better, both with a brighter star (mag. 11.3) and wider path (higher chance for an occultation); with a 3- mag. drop, it should be easy to observe visually with medium-size or large amateur telescopes. Although the Austria and Bilkis star fields are only a few deg. apart, the Bilkis field is more difficult, so pre-pointing will probably be easier for locating the target; Ernie Iverson has prepared some pre-point charts for the event. The 11.3-mag. target star is at J2000 RA 19h 02m 28.1s, Dec -11 deg. 52' 58", but it will be easier to find by pre-pointing your telescope at a brighter star before the event and turn off any tracking to let the Earth's rotation cary the target into the field of view; see the pre-point information below. Since the predicted path passes between Richmond and Washington, observers in the southern DC suburbs are more likely to have an event, but a north shift of the path is very possible so observers throughout the DC and Richmond areas are encouraged to try to observe this event from convenient locations. I hope to prepoint a telescope at home so my wife can turn on a video recorder to record the event, while I observe it from Hanover, VA, northeast of Richmond, in the path of the ZC 798 graze that occurs about another hour later; see the grazing occultation link above about that. Finder charts of different scales to locate the target star, and other event details for this good event are at Steve Preston's page for it here. PRE-POINTING YOUR TELESCOPE - If you don't have a robust go-to system, it will be MUCH EASIER to locate the target star by pre- pointing to a brighter, easier to find star with about the same declination as the target star well before the occultation. Finding the target star directly without well-calibrated setting circles or a go-to system will be very difficult, so for most, I STRONGLY ENCOURAGE that you take advantage of the pre-point opportunities briefly described below. The easiest pre-point opportunity is at 12:26:05 (or 0:26:05) am EDT (4:26:05 UT) with 5.2-mag. chi Scorpii (SAO 159793), which is 8 deg. south of 2.5-mag. delta Ophiuchi (Yed Prior) and 5 deg. west (and a little south) of 3rd-mag. zeta Ophiuchi, and 2 deg. south (and a little east) of 4th-mag. psi Scorpii. Chi Scorpii, a spectral type K0 star, is at J2000 RA 16h 13.8m, dec. -11 deg. 50'. If you point your telescope at chi Scorpii at the above time (2h 48m 10s before the occultation), then turn off all tracking and clamp the telescope so that it can't move, the target star will appear only 0.6' north of where chi Scorpii was when it is occulted by Bilkis. There are many other pre-point opportunities given in this list, including one of 5.8-mag. xi1 Librae at 11:06:49pm EDT (but it's not as good since the target star offset from it is 5.5' north; if your field of view is small, you will need to offset by approximately that amount). _ _ _ _ _ _ Aug. 2, Austria: This faint occultation will be very difficult with the 13.2-mag. star and the small magnitude drop; visual observers will have little chance to observe it, but with moderately large telescopes, CCD drift scans might record it. The target star's J2000 RA is 18h 53m 25.4s, Dec -6 deg. 22' 21", near the Scutum - south Aquila border 0.6 deg. east and a little south of M11, and a degree southwest of 5th-mag. eta Aquilae. The current weather forecasts show that it should clear up, or mostly so, by the time of this event across our region, although clouds are likely to linger in New Jersey and Delaware. At least, the star field should be easy to find, with the target star about 0.6 deg. east of M11 and not far from relatively bright stars in southern Aquila. Finder charts of different scales to locate the target star, and other event details for this newly-added (here) event are at Steve Preston's page for it here. There is an 8.8-mag. (SAO 142646) pre-point opportunity at 2:26:16 am EDT (6:26:16 UT), only 4m 32s before the occultation; the target star will be 1.6' south of where SAO 142646 was (see above for Bilkis for more about pre-pointing). The brightest pre-point opportunity is 5.2-mag. 23 Ophiuchi at 12:32:18 am, almost 2h before the occultation, but the offset to the target is large, 10.8' south. A list of several other pre-point opportunities is here. The times above, and the list, was prepared for Richmond; for Washington, DC, the times are only 5s earlier, an insignificant difference for most. _ _ _ _ Aug. 3: (2258) Viipuri is only a 27km asteroid with a large ephemeris uncertainty, so the chance for an occultation is only about 10%, worth trying from convenient locations, but not for mobile deployments. At least, it's a relatively bright star, TYC 6828-01457-1, spectral type K5. Finder charts of different scales to locate the target star, and other event details for this 9th-mag. event are at Steve Preston's page for it here. _ _ _ _ David Dunham, 2012 August 1 Phones home 301-220-0415; cell 301-526-5590 office e-mail david.dunham@kinetx.com home e-mail: dunham@starpower.net . Click here for information about other occultations in the Mid- Atlantic region through mid-September. It also has links to many other resources for observing asteroidal occultations. The events tonight are some of the best until after then; the information there will be updated to mid October near the end of August.