Aug. 13th occultation of 1 Trianguli by (89) Julia
The best asteroidal occultation in North America this year
Updated: 2005 Aug. 11
Just after 9h UT of Saturday morning, August 13 (3 am MDT), the best asteroidal occultation of the year for North America will occur from southern Baja California across the Rocky Mountains to Sasketchewan. We need your help to observe this outstanding event, the occultation of 7.6-mag. 1 Trianguli = SAO 74880 = HIP 7948 by the large 151-km asteroid (89) Julia. If an occultation occurs, there will be a 3-mag. drop lasting up to 11 seconds. Please let me know your plans for observing this occultation that could even be observed with a good pair of steadily-mounted binoculars (but a small telescope is recommended). Several observers in New Mexico plan to try the occultation, as well as a few in Colorado, but so far I have heard from nobody in Wyoming, where the chances for clear skies may be greater. Please help us observe this easy event and let me know your plans so that mobile observers don't duplicate your observation. I am especially interested in working with observers from Colorado and Wyoming, where I plan to observe the occultation from multiple sites, and could use local help with my equipment. I also have extra video cameras that can be used with any controllable telescope (that is, can be pointed at the target star, or pre-pointed to where it will be) to record the occultation, but I have only one extra VCR that I can bring, besides the 4 that will be used with my 4 small telescopes, to record the event. I also want to know what observers in southern Baja California plan to do for this event since it's likely to be clear there, also. Albuquerque, NM and Denver, CO straddle the eastern edge of this south-to-north path, but few observers live near the center or in the western half of the path; those few there are strongly encouraged to try to observe it, but mostly at least that part of the path must be covered by mobile observers. The path is shown on Steve Preston's Web site (see below), but much more detailed path maps are now available, especially for planning mobile observations, at other Web sites specified below. The path sweeps across the southern part of Baja California (La Paz just west of center) and east of Hermosillo at 9:00 UT (3:00 am MDT); then passes over western New Mexico at 9:01 UT; western Colorado and eastern Wyoming at 9:02 UT; and eastern Montana and south-central Saskatchewan at 9:03 UT. 1 Trianguli, spectral type A2, is at J2000 RA 1h 42m 05.9s, Dec. +29 deg. 30' 22" in Triangulum, about halfway between 3rd-mag. alpha Trianguli and M33, 2.4 deg. west of alpha and 0.6 deg. south of a 5th-mag. star. A finder chart is at the bottom of p. 71 of the August issue of Sky and Telescope, but more detailed ones of different scales are on Steve Preston's Web site. The star will be at rather high altitude, mostly above 45 deg., for all observers, with no twilight or moonlight. The first Clear Sky Clock forecast, a 45h prognosis, shows clouds over most of the path in the USA, unfortunately. The best area, according to it, is along the Canadian border, northernmost Montana and much of southern Saskatchewan. Farther south, the best area seems to be in southwesternmost New Mexico, along I-10 (Lordsburg and Deming area). Another mostly clear area is a narrow band in southern Wyoming. But both of these areas have poor transparency, probably indicating thin cirrus; at least, this star, bright and at high altitude, can shine through thin clouds, but such clouds would make finding the target star more difficult; possibly you could use setting circles to offset from alpha Trianguli. The weather prospects are probably very good also in southern Baja California. Sam Herchak has provided a source where Clear Sky Clock's forecasts can be obtained a little earlier, directly from Environment Canada. The forecasts are the same as Clear Sky Clock's, but without individual sites; they are just the maps that Clear Sky Clock uses. They update the maps twice daily, by 5h UT and by 17h UT. A list of stations for this occultation, sorted by distance from the central line, giving the time of closest approach, distance in km from the predicted central line, probability for an occultation, etc., is on Derek Breit's Web site. Steve Preston has prepared detailed maps of the path showing parallel lines at 5-km intervals called "tracks"; you can get them from the section about Julia (scroll down a couple of pages) on Paul Maley's web site. The tracks are numbered from the center out to N25 on the west side of the path, and to S25 on the east side of it. Multiply the track number by 5 to get the distance in km from the central line, or divide the distance in km by 5 to get your track number. We'll be using track numbers for planning the coverage by mobile observers. The predicted eastern edge of the path is 87.5 km east of center, or at track 17.5S, while the western edge is at 17.5N; there is a 50% chance for an occultation there (and much higher as one moves towards the center, where the chances are closer to 100% than 99%). A one-sigma shift to the east would move the eastern edge to 114 km east of center or track 22.7S; there is a 16% chance for an occultation there, and similarly for track 22.7N to the west. Even more detail than on these maps can be found at Charlie Ridgway's interactive Google maps site; he not only shows the usual limits for this event (green line for the center, blue lines for the predicted limits, and orange ones for the 1-sigma limits), but also has added Steve Preston's tracks as pink lines. The pink lines aren't labelled, but he gives thicker pink lines at 5-track (25 km) intervals so it's pretty easy to keep track of them. And Kiwi Geoff has used this event to show a new capability, to plot a specified offset line (actually, two of them, one on each side of center) at a specified distance in km from the center that can be used with the same Google Earth database to zoom into any desired scale; you can access it here. Some observers have already made plans to occupy certain lines, pending knowledge of fixed-site attempts; they don't want to travel to a remote site only to duplicate someone's chord at a fixed observatory. So let us know your plans. James Thompson and I plan to observe this event, scheduled to arrive in Colorado Springs, CO at 10:15 am MDT Aug. 12. We will drive north to Greeley, where we hope to meet Dick Dietz to help us with the 4 stations that we want to deploy across the path, and to obtain a last check of the Clear Sky Clock forecast. We will probably deploy the stations across the path along either I-80 west of Cheyenne, WY, or if necessary farther north along I-25 and US 20 east and west of Casper, WY. In the less likely case that the forecast is good for western Colorado, we'll drive the shorter distance to observe from sites near I-70 west of Denver. But we will also check the forecast from Colorado Springs, and may drive south to southern New Mexico if the forecast remains better for that area. Since we'll be pre-pointing telescopes, we'll want to start deploying as soon as it gets dark, so it needs to be clear, or mostly so, in the target area in the evening as well as during the early morning. Others are invited to help us straddle the path with as many stations as possible to better determine the size and shape of (89) Julia. Below is an updated list of observers who plan to try to observe the occultation; there are a few changes from the list that I distributed before. This is given in 5-km-wide "tracks" explained above. Track N17.4 predicted western limit (but it could be farther west) N15 James Thompson, mobile with Dunham unit N12 approximately, for Sam Herchak mobile (coming from Phoenix area) N10 Kevin McKeown, NM mobile from Albuquerque N8.2 Sleaford Observatory, Saskatchewan N6.8 Datil, NM mobile from Soccoro N5.2 Dunham remote #1 N3.6 NM, mobile from Socorro N2 Pie Town, NM portable from Socorro C0 Paul Maley & El Paso 1 only if weather good enough to try it S2 Paul Maley & El Paso 2 only if weather good enough to try it S4 Paul Maley & El Paso 3 only if weather good enough to try it S6 Dunham remote #2 S7.5 NM, Bill Stein mobile S9.2 Magdalena, NM Bill Ryan, fixed site S10.2 Dunham mobile S11.2 Miners View, CO C14 observatory Tina Ruhland S12.0 Regina, SK Vance Petriew fixed observatory S13.5 NM Rich Richins mobile S14.6 Twining Observatory, near Albuquerque? S15.8 Etscorn Observatory, Socorro, NM, Dan Klinglesmith S17.4 predicted eastern limit (but it could be farther east) S18 around this chord, a few observers in Albuquerque, NM S36 Kiowa Observatory, Scott Donnell Some tracks for a few key places: N2.4 La Paz, Baja N1.8 Casper, WY S14 Laramie, WY S15.8 San Jose del Cabo, Baja (duplicates Etscorn Obs., better to go farther northeast) S23.7 Boulder, CO If not above, you can determine your track by looking at the station list on Derek Breit's Web site and divide the distance in km in the left column by 5 to get the track. Or you can determine it from one of the many on-line maps. This is my last update of this Web site. For any future chances, see Derek Breit's Web site above. I'll be reachable by e-mail, best at dunham@starpower.net, until 4 am EDT Aug. 12, and possibly after that if I can find a wifi connection or get internet access. But the best way to reach me after that time will be by car phone, see below. David Dunham, IOTA, 2005 August 11, 23h UT e-mail home dunham@starpower.net office david.dunham@jhuapl.edu Phone home 301-474-4722; office 240-228-5609; car 301-526-5590