Well-Observed July 17/18 Spectacular Antares Grazing Occultation
The graze was timed by dozens of observers in 11 expeditions from Olympia, WA to Atlanta, GA
Updated: 2005 July 19, 5 pm EDT
Message to Patrick Wiggins in Tooele, Utah, giving a summary of the currently known expeditions that observed Sunday night's Antares grazing occultation and giving some advice on reporting observations. ___________ Patrick, Many thanks for your observation copied below. First I give a summary of the successful expeditions known to me so far, and to briefly report the results of the expedition south of Lubbock, TX that I was in; I'm copying this to others who aren't in the IOTAoccultations egroup who participated so they know about the efforts reported on that e-group, too. I have some remarks about your and Hal Povenmire's observations that could benefit others for their reporting, too. ____________________________________________ Successful expeditions: 1. Olympia, WA, Walter Morgan, about a dozen stations, many with multiple events recorded, several videos. 2. Burns Junction, OR, David Becker, video, one station. 3. Kanosh, UT, Patrick Wiggins & Harold Povenmire, see below. 4. Mexican Hat, UT, Sandy Bumgarner, video, one station (judging from his coordinates, he was in s.e. Utah, probably near Mexican Hat, rather than near Mexican Water, AZ, as originally planned). 5. n. of Tahoka, TX, David Dunham & Tom Heisey, 4 stations (1 remote), 3 videos, each station had 2 D's and 2 R's except Mike McCants at the s. station, who had just 1 D and 1 R (but we might find more with a careful review of the video tapes). We could see cirrus from thunderstorms over NM very low in the west; otherwise, it was almost completely clear (and clear around the Moon), and fortunately the wind didn't pick up until a couple of minutes after the graze. 6. s.w. of Post, TX, Craig Smith, one station, video, I think he said 3 D's and 3 R's. 7. s. of Anson, TX, Rick Frankenberger & Don Stockbauer, 2 stations, both video, 6 D's and 6 R's at one and 1 D and 1 R at the other. 8. Ranger, TX, Ron DiIulio, video, 1 station. 9. n. of Stephenville, TX, Ben Hudgens, several gradual events. He said "we were on the edge of the thin cloud cover" and so were successful, I suppose implying that there was increasing clouds east of there, as forecast, but see next. 10. w. of Corsicana, TX, Bob Sandy, 2 stations, each with about 5 D's and 5 R's, through thin cloud that posed no problem. 11. e. of Atlanta, GA, Mike Kazmierczak, 4 D's and 4 R's, several gradual. It looks like we'll be able to produce a very interesting profile from all these observations with multiple events from several stations spread over a wide range of longitude. My condolences to the Albuquerque observers who were all clouded out, and many thanks to the Ramotowskis for taking care of me during my unexpected stay in Albuquerque the night before thanks to thunderstorms in the East that caused me to miss my connecting flight Saturday evening to Midland-Odessa. _________________________ (Patrick) At 04:47 AM 7/18/2005, you wrote: >Regarding the Antares graze of 18 JUL 2005 UT. > >Hi David, > >As I voice mailed you I had a pretty good graze last evening. Hal >Provenmire said he saw a number of events also. > >My coordinates were: > >Near Kanosh, Utah >38 46.8182 N >112 30.1115 W >1522.0 M > >Mr. Provenmire apparently did not get coordinates for his site but said >since he was so close to me (he was about 100 meters southeast of me) he >would use my coordinates. - You and he should zoom in on the site using http:\\maps.google.com to try to determine his location relative to yours to an accuracy of 20 meters or better; 100 meters is too far to use the same coordinates, the events will be (or rather, must have been) noticeably different at locations that far apart. >Playing back the tape I saw three complete occultations, 2 "flicker" >events (all listed below) and a few frames on the tape where the star >almost faded out but not quite. > >Also I was kind of surprised that the star did not disappear immediately, >sometimes taking half a second or so to vanish. - That's because the star is a red giant star with angular diameter about 0.03", which subtends about 50 meters at the Moon's distance; especially with the grazing geometry, all of the events on video should be gradual, taking a few (if a steep slope covers or uncovers the star) to several video frames (or even more than a second for a very gradual slope). In fact, observers should report the start and end times of each D and each R because Antares is large enough that effectively you get two chords across the profile for each station, with separation equal to the subtended diameter (but more on the ground due to projection). Diffraction has an insignificant effect with such a large star, so unlike events dominated by diffraction fading, where the geometric occultation occurs at the 1/4th intensity level, for large stars like Antares it (that is, the geometrical occultation for the center of the star) just occurs at the half intensity level. One observer reported times for the 30% intensity level but that's wrong, if you report just one time, it should be for the 50% level. But it's better to give start and end times (and I think the 50% level time as well). >Here's the data I read off the video tape: > >Ingress 03:50:51 0108.5 >Egress 03:50:59 0883.9 > >Ingress 03:51:27 0511.3 >Egress 03:52:38 0548.3 > >Flicker 03:52:40 0283.3 - By "flicker", do you mean a partial blink? That is, just a temporary dimming with no complete disappearance? Then you should give the "start of disappearance" (the start of the dimming); the time of maximum dimming and its amount (approximate percentage of the unocculted brightness); and the time of the "end of reappearance" (end of the dimming). Anyway, this is certainly an interesting set of observations, I'm jealous since you had more action than any of us had at Tahoka, TX. David >Flicker 03:52:40 0783.9 > >Ingress 03:52:40 0984.1 >Egress 03:52:49 0192.2 > >Equipment used: > >Celestron 5 telescope >Garmin OEM GPS 16-HVS >GPS based precision time inserter - was that an STVastro, or another one? >Supercircuits PC164C CCD camera > >All in all a good evening. > >Patrick An example of the International Lunar Occultation Centre's "e-mail76" report form for reporting grazing occultation observations is here with a comprehensive explanation here. The example, for a graze of a 5th-mag. star observed in Pennsylvania last March that had several gradual events due to Fresnel diffraction, shows (especially for stations B and C) how to report the start and end of gradual disappearances and reappearances that were so common with the Antares graze. If you use the form, be careful to keep the columns lined up properly; with your editor, be sure to use a fixed-space font such as Courier. Reports in this format can be generated much more easily with a menu system in Dave Herald's Occult program if you have it (the installation files for it can be downloaded from IOTA's main Web site. Admittedly the form, optimized years ago for command language computer processing, is not user-friendly. If you have trouble producing it, and/or don't have the Occult or Lunar Occultation Workbench programs with thier relatively easy-to-use menu systems, you can just report your location(s) and timings in any organized unambiguous manner (please give the times in U.T. rather than local time) in a plain text file or e-mail message. Extensive prediction information for the 2005 July 17/18 Antares occultation and graze with maps, predicted lunar profiles, etc., are here. David Dunham, e-mail dunham@starpower.net Phones home 301-474-4722; cell 301-526-5590