17-km Asteroid (955) Alstede Occ'n of 9.5-mag. PPM 90693 = TYC 1203-01745-1, 2005 Nov. 26 UT, Newfoundland to Mexico
The path shifted almost two path-widths north, where it was recorded at one of my remote stations at Oraville, Maryland.
New: 2005 Nov. 28
On Friday, Nov. 25th, just before 8 pm, there was an occultation of a 9.5-mag. star in Pisces by the small asteroid (955) Alstede predicted for Cambridge & St. James, MD; Richmond, VA; and Greensboro & Charlotte, NC. Accuweather predicted 30 - 50% chance of cirrus for these events three days in advance, and it turned out to be clear in those areas. Unfortunately, Roger Venable was clouded out in Georgia. My account of the occultation is below, followed by some prediction information, including the station list, which you can see if you were within the actual path, which apparently extended from about +14 to +32 km. _______________________ For Nov. 25/26's occultation of PPM 90693 = TYC 1203-01745-1 by (955) Alstede, I ran two remote stations in southern Maryland, about 40 - 50 miles southwest of Washington, DC, at 27 km and 12 km north of Steve Preston's predicted central line. Both stations used 8- inch SCT's with video recordings and GPS time insertion verified by alarms from "atomic" travel alarm clocks. I also tried to observe from a 3rd site at 6 km southwest of the central line, but there I acquired and started recording the target star at 0:59:58 UT, almost 1.5 minutes after the predicted time of the event, too late. The north shift of the path meant that the actual path must have passed over n.w. Nova Scotia; Mass. just n. of Plymouth; s. Rhode Is.; e. Long Island; east-central & Millville, NJ; central Delaware; Easton & Nanjemoy, MD; Bowling Green & Oliver, VA; w.-central NC; n.w. SC; s.e. suburbs of Atlanta, GA; Mobile, AL; and the s.e. parts of New Orleans. The IR satellite image shows that it was clear from Mass. to central Alabama - did anyone else try this one other than those mentioned below? But Roger Venable said he was clouded out northwest of Augusta, GA. However, at the northern remote station at +27 km, in back of a construction trailer in back of a popular tavern at Oraville, Maryland (permission obtained from the trailer owner), at long. 76 deg. 41.7228' W., lat. +38 deg. 25.0489', h 46m - WGS84, the target star drifted into the field of view at 0:58:01 UT and left it at 0:59:17 UT. A 2.4-second occultation (close to the predicted 2.3s central duration) occurred there close to the predicted time: U.T. h m s 0:58:30.78 +/-0.01s Disappearance 0:58:33.18 +/-0.01s Reappearance Each event lasted 3 - 4 fields. The telescope was pre-pointed in twilight 2h 14m before the occultation. This was farther north than I had intended, but didn't discover my "navigation" error until after I had set it up, and there wasn't time to move it, only time to go on to the next site. Of course, it's a good thing I had a station there rather than at the intended location of +18 north, which would have probably been near the southern limit and a possible miss. The southern remote station was at +12 or +13 km, next to a closed church school in southern Hollywood, Maryland, at long. 76 deg. 33.5066' W., lat. +38 deg. 19.9425', h 41m - WGS84, the target star drifted into the field of view at 0:57:56 UT and left it at 0:59:10 UT, and was not occulted. Wayne Warren tried to observe at +6 km, but like me at -6 km, acquired the target star a few minutes too late. My attempt at St. James at -6 km from predicted center, in a driveway (homeowner's permission obtained) at long. 76 deg. 24' 33.4" W., lat. +38 deg. 13' 05.5", h 90 ft. - WGS84, using a 5-inch SCT I acquired the target star too late, as mentioned above. Since the actual path passed farther north, no occultation by Alstede occurred at these two locations in the predicted path, but it would have been better to have recordings there to check for possible satellites of the asteroid. Roger Harvey observed at his fixed observatory in Concord, NC at 26 km south of the predicted center, and had no occultation, at long. 80.55789 deg. W., lat. 35.37345 deg., h 717 ft. using his 29-inch telescope. The night before, my family tried to observe the lunar grazing occultation of sigma Leonis from Nags Head, NC, hoping to set up six telescopes, but getting only 4 of them up before the graze. Unfortunately, thick clouds moved in with a strong wind from the ocean, and checking the IR weather satellite view afterwards showed that it was overcast, or mostly cloudy, along the whole path across North Carolina & Tennessee; the Clear Sky Clock forecast was much more optimistic for e. NC. At the one remote station that I was able to start when the star appeared briefly several minutes before the graze, the Moon was recorded only a few times in breaks in brief partial breaks in the clouds, but no contacts occurred then. Returning home at 4 pm to leave off my wife & son, who were by then not interested in further observation, I unloaded three of the telescopes from my minivan to have less "clutter" to shift through for the Alstede event, when I knew I could at most run 3 stations. But that caused a problem, because after the graze, my wife was using the 5-inch SCT that I now had in St. James, MD for Alstede, and she had removed the finder and the screw that holds its mount to the mounting bracket on the telescope, and she kept that screw, meaning to give it to me later, but forgot. So in St. James, I couldn't firmly mount the finder to the scope. Lesson learned #1 - if you have an extra telescope, bring it, just in case. I was able to collimate the finder quickly on a star low in the sky, but when I moved it to the approx. 60 deg. of Mars, not far from the target star, the finder shifted and I wasn't able to re-collimate. I tried for a few critical moments without success, but finally shoved the finder support as hard as I could into the bracket, and it held, even without the screw. But I still couldn't collimate it, until I finally had the idea to remove the video camera, and put in an eyepiece without refocusing (it was focused for the video), and then was able to see the out-of-focus disk of Mars that I was able to center, collimate the finder, and put the video camera back, refocused on Mars, and then found the target star 2 - 3 minutes later, but as noted above, too late. Lesson learned #2 - if you have trouble collimating the finder, do it with an eyepiece on a bright object so you can refocus with the video on that object after the visual collimation. If I had thought of that earlier, I would have succeeded. But it turned out to be not so important since the main show was farther north (north shift about 27 km), continuing the trend of north shifts with recent events. _______________________ The star was at J2000 RA 1h 20m 54.6s, Dec +20 deg. 36' 00", in Pisces 0.6 deg. west of 7.4-mag. SAO 74682, halfway between 5th-mag. rho and xi Piscium, all about 8 deg. west of beta and gamma Arietis. The star was at very high altitude and being so bright, observation even in light-polluted areas with lots of trees was possible. A list of stations for this occultation, listed by distance in km from the predicted central line, can be found on Derek Breit's Web site. You can search for your, or your town's or observatory's, name to see just when the occultation is predicted for your area (that time should be accurate to within 15 seconds or so; it will be 0:58 UT, or 7:58 pm EST, in Del., s. MD, & VA, and 7:59 pm in NC & nw SC), the probability for having an occultation there, and the predicted star altitude at the time. David Dunham