July 17/18 Antares Occultation and Graze in North America
Expeditions planned from Washington State to North Carolina
Detailed IOTA predictions across the USA and Vancouver Island
ACLPPP profiles & suggested ranges given; detailed maps from Albuquerque, NM to Corsicana, TX
Updated: 2005 July 15, 11 pm EDT
On Sunday night, July 17/18, the waxing gibbous Moon will occult the red giant star Antares (ZC 2366) for observers in the western and southern USA, Mexico, Central America, the Caribbean Sea, and northern South America; I think also the coast of Vancouver Island, B.C., will have a graze, shortly before sunset. A map showing the full region of visibility of this July 18th (UT) Antares occultation, and predictions of the total lunar occultation of Antares for many dozens of cities across North and Central America, is on IOTA's main Web site. During 2005, the Antares lunar occultation zones shift progressively south so this will be the last chance for most North American observes to see an occultation of this red giant star for a few years. Methods for timing occultations are described here. Of most interest will be the dark limb grazing occultation of Antares visible near the northern limit line extending from Washington State to Texas and on to northeastern North Carolina. Within an approximately mile-wide band generally just south of the predicted limit (the event occurs mainly in a low region of the Moon), you can see the bright red star disappear and reappear a few to several times among mountains and craters near the lunar north pole, with most of the events noticeably gradual, lasting even more than a second, due to the star's large angular diameter of about 0.03". Partial blinks might be seen as lunar mountain tops cover and uncover only part of the star, and similarly you might see the star reappear faintly only briefly in lunar valleys. The Accuweather forecast remains generally good for the western half of the path and poor for the eastern half. The cloud cover percentage/probability % however has dropped to 53% of high clouds (20,000-ft.) from North Carolina to Mississippi, so observers there may have some chance. The cloud cover will probably be patchy, meaning mobility could help a lot. Unfortunately, Corsicana has the worst odds, with 70% high clouds expected. In Texas, Abilene may be the best place, with only scattered (18%) cirrus. The cirrus increases to 35% at Lubbock and 51% of 20,000-ft. clouds at Albuquerque. Farther northwest, conditions are very good, with only scattered cirrus at Mexican Hat, Utah, and clear skies from there all the way to Olympia, Washington. Of course, this can change, and thunderstorms are likely to form at places hard to predict from the Four Corners area eastward; remaining mobile to be able to get into clear areas away from thunderstorms could be advantageous. Also, tomorrow (Sat.) afternoon, a Clear Sky Clock forecast should become available that should be better than Accuweather. Derek Breit has posted general maps showing the northern limit across the USA from Washington State to North Carolina. Detailed maps are shown for some areas, including Mexican Water in n.e. Arizona; Albuquerque, NM; and Lubbock, TX. You can find these, and details of the graze using data generated with the Occult program, here. The Occult information doesn't include the effect of the secondary star on the profile, but its effect is small. That is included in the ACLPPP profile with link given below. Breit does include the correction for height above sealevel on his maps. That correction, as well as the fact that this graze occurs in a low part of the Moon, means that the actual path will be at least a couple of miles south of the line that Derek has calculated so that observers on his plotted northern limit line will see no occultation; he has plotted on the detailed maps green lines where multiple occultations of Antares are more likely. Note below my suggested ranges for observers from the predicted line in different areas. Even better are these Web-based interactive maps prepared by Charlie Ridgway in New York City. No occultation is likely as seen from the northern limit line, but multiple events can be seen during the graze from locations generally 1 to 3 miles south of the plotted line in the low area of the Moon where this graze occurs. Unfortunately, the interactive map does not work with some Apple computers and with older PC windows Web browsers (many Apple users have said it works fine for them). If it doesn't work for you, Derek Breit will generate maps for you and post on his Web site. Write to him at breit_ideas@hotmail.com - All he needs is the desired Longitude range and the elevation (height above sea level) of the area. James Thompson used the above Web site to obtain rather detailed maps of the Occult sealevel northern limit line from Albuquerque, NM to Corsicana, TX, and placed them in two word files: click here for Tahoka to Corsicana, TX click here for Tahoka to Albuquerque, NM The scale of these maps can be judged in many cases from the rectangular mile-between-roads grid in many of these rural areas; when the Word file is printed, the scale is 1 inch = 1.82 miles. The graze zone passes a couple of miles north of Tahoka, which is about 30 miles south of Lubbock, TX. I know of at least 10 expeditions that will try to observe this graze: 1. Olympia, Washington: Walter Morgan, WVM13@aol.com , is leading this effort, but since he will be far from his home in California, he might not be able to receive e-mail over the weekend before the graze. Anyone interested in this expedition should also contact Steve Preston at stevepr@netstevepr.com since he will likely be able to receive e-mail up to early afternoon Sunday. The expedition will be at Mottman Rd SW at Johnson Rd. 2. Burns Junction, southeastern Oregon: David Becker, from Boise, ID, rupesrecta@mac.com . An alternate site is where the path crossed Route 95 north of Winnemucca, Nevada. 3. Probably near Kanosh, Utah, near I-15: Patrick Wiggins, paw@trilobyte.net . 4. Mexican Water, n.e. Arizona: Sandy Bumgarner, sandy@vbbn.com , and Harold Povenmire, Katiegraze1@aol.com , but he prefers phone calls, either at his summer residence in Flagstaff, AZ, phone 928-526-5555, ext. 623, or cell 321-544-5658. 5a. Corrales (n.w. suburb of Albuquerque), NM: Ed Isenberg, astronomy@isenberg-family.net , phone 505-922-1072, plans to observe with half a dozen others at the intersection of Meadowlark Lane and Loma Larga at lat. 35 deg. 13' 25.5" N., long. 106 deg. 38' 25.5" W, h 4952 ft. = 1510m. 5b. Albuquerque, NM: Becky Ramotowski, beckster@cotse.net - I don't know if this will be a separate expedition or if she will just join the Corrales (4a) expedition. 6. Lubbock, TX: Tom Heisley, Tom@tomheisey.com . I plan to join his expedition, arriving at Midland-Odessa Sat. evening, July 16, and will drive north in a rental car to meet observers from Lubbock; observers from Midland may join this expedition, too. I will be flexible, willing to travel as far west as Albuquerque or as far east as Corsicana to observe this graze. If the weather looks good in the Lubbock area, I plan to observe from sites along County Road R from where it intersects Route 400 to about 2 miles north of there. That intersection is 0.7 mile northeast (along Route 400) of where Route 400 exits from US 87 about two miles north of Tahoka, TX, about 30 miles south of Lubbock. If anyone wants to join me, they can meet me there at 9:30 pm CDT Sunday. I will have an extra telescope and two extra video systems (fit into any standard 1.25" eyepiece holder); it would be good if someone could join me to use them. But keep in touch by cell phone, mine is 301-526-5590 (but during the Lamberta occultation earlier this month, I found out that cell phone coverage is spotty in Tahoka, unfortunately; let me know well beforehand (by cell phone Sunday afternoon, or by e-mail at dunham@starpower.net by early Sunday morning) if you might be able to join this effort. Beware that maps.google shows two county road R's, north-south roads on opposite sides of US 87; the one of interest is the one east of US 87 (there may be a mistake in one of their names). I will scan an annotated version of the map (the first one in the Tahoka to Corsicana Word file with link above) and send that to Derek Breit, who can post it on his Web site, since I probably won't have a chance to post it here. In the graze zone in the vicinity of Tahoka, the observation period when you should be recording for multiple events is from 4:17 to 4:21 UT, or 11:17 to 11:21 pm CDT. 7. north of Stephenville, TX: Ben Hudgens, bhudgens@our-town.com , phone 254-968-2881. 8. Corsicana, TX: Bob Sandy is leading a rather large expedition; read his recent message with details here. Rick Frankenberger, rickf@stic.net , from San Antonio is a co-leader of this effort; if clouds threaten Corsicana, near I-45 southeast of Dallas, his expedition will try to observe from alternate sites as far west as Abilene, TX. 9. Near Atlanta, GA: Mike Kazmierczak, mkaz2@beow.org . 10. Near Greenville, NC: Bill All, billyrall@earthlink.net . Bill says he may not time the graze, that this is mainly a local effort, but so far I know of no others planned in the Carolinas. Let me know if you plan to observe the graze from a site separate from the ones listed above. Since I will be away from home, and Wayne Warren will also be out of town until too late Sunday evening, I know of no effort to try to observe the graze by DC-area observers. Others in the Mid- Atlantic region might want to join Bill All's effort. Here are the IOTA occultation limit predictions (Grazreg) now extending across the U.S.A. from Washington State to North Carolina, and northwestward into daylight where the path skirts the southwestern coast of Vancouver Island, British Columbia, specifically from longitude 127.0 W. to 75.0 W.), in the file ant718nm.txt . Below I give ACLPPP profiles for several locations along the graze path and then recommended ranges for observers based on them. ACLPPP profiles Olympia, WA area Burns Junction, OR area Kanosh, UT area Mexican Water, AZ area Albuquerque, NM area Snyder, TX region Stephenville, TX area Corsicana, TX area Shreveport, LA region Jackson, MS region Alabama Atlanta, GA region Columbia, SC region Greenville, NC region Note that the correction for height above sea level is large for this graze and must be taken into account for heights greater than about 500 feet. You can see how to do that, and in general how to use these predictions and the ACLPPP profile, here. But I've gone through the process to figure out a recommended range of distances using those profiles, and also figured out the height correction, for the known expeditions. All distances below are measured perpendicularly to the northern limit line, not due north or due south (so if I say 1.0 mile south for an observer in Washington State, where the path extends from northwest to southeast, the distance is measured from the line perpendicularly to it towards the southwest). The correction for height above sea level is proportional to the height and always moves the path towards the south. Multiply the height above sea level by the factors below to obtain the shift due to the height: West Height (or elevation) longitude, factor, degrees dimensionless 120 1.40 110 1.56 100 1.79 90 1.72 80 1.51 You can interpolate these values for intermediate longitudes. But the shifts for the known expedition areas have all been calculated. Notice that IN MOST AREAS, the graze occurs in a low part of the Moon; that and the height correction will cause observers along most of the path to have a MISS (NO OCCULTATION) if they observe from the northern limit line, or not far enough south of it. So the suggested ranges below are important for locating your sites. When considering ranges for observers, note that there are three different reference northern limit lines: The IOTA Grazereg sea level limit with link given above for the data; the Occult sea level limit used by Derek Breit for his State maps and by Charlie Ridgway for the interactive maps with links to them above; and the Occult limit corrected for height above sea level (used by Derek for his detailed maps). Fortunately, the IOTA and Occult limits are close to each other, crossing (zero difference) in Texas, with differences in other areas not really significant considering errors in the predicted profile. The ranges below are generally from 1.5 to 2.0 miles wide; a lone observer should aim for the middle of the range, but with two or more observers, try to spread out across the range to try to map the lunar profile better. N is north and S is south, measured perpendicularly to the path; all distances are in miles except for heights above sea level, which are in feet. The "Range from IOTA limit" is the range estimated from the ACLPPP profile and is thus the range AFTER the correction for height above sea level has been applied, when appropriate. But usually it's easier to just combine the height correction with the range, which I've done in the "Range from IOTA sea level limit" column, and then the last column has the same thing from the Occult sea level limit. Used height Range from Range from Range from above IOTA sea Occult sea Area IOTA limit sea level level limit level limit Washington 1.0S - 2.5S 0 1.0S - 2.5S 0.7S - 2.2S s.e. Oregon 1.0S - 3.0S 3940 2.1S - 4.1S 1.9S - 3.9S central Utah 1.0S - 3.0S 5015 2.4S - 4.4S 2.2S - 4.2S n.e. Arizona 1.8S - 3.0S 4940 3.3S - 4.5S 3.2S - 4.4S central N.Mex. 1.0S - 3.5S 4900 2.6S - 5.1S 2.5S - 5.0S Tahoka, TX area 0.3S - 2.3S 3100 1.3S - 3.3S 1.3S - 3.3S Snyder, TX area 0.0S - 2.0S 2000 0.7S - 2.7S 0.7S - 2.7S Stephenville,TX 0.0S - 2.0S 700 0.3S - 2.3S 0.3S - 2.3S Corsicana, TX 0.2S - 2.0S 500 0.4S - 2.2S 0.4S - 2.2S Louisiana & MS 1.5N - 0.5S 0 1.5N - 0.5S 1.4N - 0.6S Alabama & Geogia 1.0N - 1.0S 780 0.8N - 1.2S 0.7N - 1.3S Carolinas 1.0N - 1.0S 0 1.0N - 1.0S 0.8N - 1.2S David Dunham, e-mail dunham@starpower.net Phones home 301-474-4722; cell 301-526-5590