Chuck Hards wrote:
Is anyone planning to observe the Spica occultation on Christmas morning? Looks like it will happen at about 6:35 or so, MST. We are near the southern limit so while technically it won't be graze, it will be darn close for SLC.
This would be a good event to record on video, re-emergence especially.
Researching the occultation further I found that David Dunham (head of the International Occultation Timing Association) is coming to Utah to record the graze. Anyone here interested in traveling south to see the graze? I see there's a spot very near Cove Fort that should work well. If you've never seen a graze of a bright star it really is a fun thing to watch. Basically the idea is to position oneself so the star does not _quite_ go behind the Moon and instead briefly hides behind lunar mountain tops and pops out in the valleys. A good graze will produce several of these "blinks". I'll append a copy of David's email on the subject below. Patrick ALPHA VIRGINIS, 2005 Dec. 25 (Sunday morning), Moon 33% sunlit This is the best 1st-magnitude occultation in North America this year, the reappearance and graze being visible rather easily to the naked eye near and north of the southern limit in the western USA and Canada. There is nothing comparable to it in North America next year for 1st-magnitude stars, as you can see in my article about 2006 lunar occultations in the January issue of Sky and Telescope. Spica (ZC 1925) is a close binary star but with a separation less than a milliarcsecond that can't be resolved by a lunar occultation. There's a claim that it has another 7th-mag. companion to the south a few hundredths of an arc second, based on early graze observations, but instead those faint and gradual event observations may have been just due to Fresnel diffraction; more recent graze videos during the last opportunity about ten years ago did not reveal this companion. So it will be interesting to see what we find this time with this very good Christmas morning opportunity. A good overview of the occultation is in the December issue of Sky and Telescope, and online at http://skyandtelescope.com/observing/objects/occultations/article_1620_1.asp You can get to this from S&T's main page at http://skyandtelescope.com and clicking on the Spica occultation item just after the news notes at the top. This shows a diagram showing the paths of the star behind the Moon's disk for several major US cities, and maps for both the disappearance and reappearance from which you can tell the approximate U.T., and the Sun and Moon altitudes, for any location in the USA, southern Canada, and n.e. Mexico. The occultation will occur after sunrise east of Denver; it will occur near 13h UT (5am PST, 6am MST, 7am CST, and 8am EST). A small map showing the region of visibility, and local predictions for hundreds of cities, is on the IOTA Web site at http://www.lunar-occultations.com/iota/bstar/1225zc1925.htm . A spectacular graze will be visible from the southern limit in the West. Just after 13:30 UT, the path passes between Chehalis and Olympia, WA; then near The Dalles, Fossil, and Burns, OR; after 13:40 UT, west of Wells, NV and s.w. of Wendover, UT; after 13:50 UT, over Cove Fort and Junction, UT (Sun alt. -11 deg. there); after 14:00 UT, over Ganado, AZ; after 14:10 UT, over Zuni and n. of Truth or Consequences, NM, and between Las Cruces and Alamogordo; at 14:10 UT, sunrise at the NM-TX border a short distance east of El Paso, then over Big Bend National Park at 14:20 UT. The path then crosses n.e. Mexico, passing a short distance n.e. of Monterrey, and s.w. of Santander Jimenez between Ciudad Victoria and San Fernando. You can see general maps of the graze path for the different States on Derek Breit's Web site at http://www.poyntsource.com/BREIT_IDEAS/Spica.htm You can zoom in on the path to see great detail on Charlie Ridgway's interactive Web site at http://digitalmagic.i8.com/Astronomy/Occultations/05/Grazes/051225_Spica.htm... This is the sea level limit; I've also sent him data so that he might later show the limit as shifted to the s.w. a mile or so for elevations above sea level of 5000 ft. and 6000 ft. Later, I will distribute information about offsets from the Occult southern limit line to specify a "graze range" of distances from the limit line to optimize chances for observing multiple events, for known expeditions. Derek Breit, breit_ideas@hotmail.com , plans to observe the graze from Oregon; he shows possible sites on his Oregon planning page on his Web site given above. I plan to observe the graze myself from Junction, UT.