Good Lunar Pleiades Passage Sun. night Feb. 5/6, for western North America
More detailed maps of the Electra graze path across southern California, with the graze zone clearly marked for maps of the area north of Camarillo and in n.w. Orange County, with preliminary expedition information, have been added
Updated: 2006 February 2, 8:45 pm EST
The Moon, just a day past first quarter (61% sunlit), will occult dozens of stars in the Pleiades for observers throughout western North America late Sunday night, February 5/6. The UT date is Feb. 6 for all events, but it is late Sunday evening, or just after midnight, local time. Extensive predictions of the total occultations are on the main IOTA Web site or, specifically for the occultations of the seven brightest Pleaides stars predicted for dozens of cities, including maps showing the region of visibility of each occultation, click here and click on "view" for each event in the "predictions" column of the table. Earlier this month, many IOTA observers received a file that includes IOTA predictions for 2006 either your location, or for one nearby; if not, I can provide one upon request. When renamed to .zip and unzipped, one of the files produced is boccnxxx.006 where xxx is the station number in IOTA's "B" region covering the southwestern USA; that file includes predictions of total lunar occultations for the location, including of the numerous Pleiades stars that will occur Sunday night. For information on timing occultations, click here. If you can locate yourself within a mile or two of the northern or southern limits of the region of visibility of these occultations, you can see a spectacular grazing occultation, with the star disappearing and reappearing amoung mountains and craters in the lunar polar regions as the star appears to move along a line tangent to the Moon's disk. The northern limits of 4 3rd and 4th- mag. stars during the Feb. 6 (UT) passage are shown on my map on p. 71 of this month's issue of Sky and Telescope. You can see these and 4 other graze paths on Charlie Ridgway's Web site which is an interactive map that you can zoom in for much more details, like the ones he has for asteroidal occultations. I have captured and posted that map in a Word file here (beware, the first page is blank; the 2nd page has the color code key; and the third page has the map). *** CAUTION *** All of the northern-limit grazes will occur in a shallow area of the Moon so that you need to be a mile or so SOUTH of the predicted limit line (shown in yellow on Ridgway's individual graze interactive maps; more about them is on the Web site); if you observe from the predicted northern limit line, you will have no occultation, only a frustratingly-close miss. Observers even several miles south of the northern limits might see the star disappear, then quickly reappear and disappear again, before reappearing on the bright side (hard to see) a few to several minutes later, but the chances are much higher for seeing many successive quick occultations of the star within the graze zone. Fresnel diffraction of the star's light at the edge of the Moon, as well as possible duplicity of the star, will cause many of the events to appear gradual or partial, even lasting a second or more in some cases. One of the best grazing occultations (or grazes for short) during the Pleiades passage will be one of 3.7-mag. Electra visible from parts of Los Angeles and other areas of southern California. Rather than use Charlie Ridgway's site for the Electra graze, it is better now to use one set up by Kiwi Geoff described a couple of paragraphs below since it allows plotting two offset lines independently to show the multiple events graze zone well. The graze zone for Electra is very narrow, only 1.0 km wide. Some maps of the Electra graze path across southern California are in a 1-megabyte Word file here, but the narrow (only 1.0 km wide) grazing occultation zone is better shown in the maps in this 11-megabyte Word file here (BUT BEWARE, this is an OLD file, see the note for the Aguanga - I-8 area map below) with even more detail shown for areas selected either for dense population or good potential sites in NEW maps in Word files that show the multiple-events grazing occultation zone between two prominent gray lines produced from Kiwi Geoff's Web site noted above (ignore the yellow line on these charts; it's hard to see, anyway): west region s. of Santa Maria, 380 kilobytes n. of Camarillo to Thousand Oaks, 1.8 megabytes Los Angeles, Agoura Hills to Norwalk, 1.9 megabytes - for this, the first maps are from West L.A. to Norwalk, then from W. Sunset Blvd. to Agoura Hills. north Orange County, Buena Park - Irvine Lake, 870 kilobytes n.e. Orange County expedition site details, 11.3 megabytes - Includes aerial photography images that make this file large Murietta - e. Temecula alternate site details, 1.4 megabytes southern Imperial Valley, 361 kilobytes An OLD STYLE map made before from Ridgway's Web site shows the area Aguanga area, & I-8 & Somerton, AZ, 2.0 megabytes, so unlike the ones above, just this one plots only the s. edge of the 1.0-km- wide graze zone as the southern gray line while the other lines need to be ignored. If you don't have a high-speed connection to get one of the larger files, let me know and I can email you selected maps in smaller files. The maps have a scale in both miles and kilometers in the lower left corner. North of the northern edge of the graze zone, NO occultation of the star will occur, only a close miss, including AT the yellow line, so it's important for mobile observers not to go too far north. The location of the gray lines takes into account the 0.40 factor southward shift for height above sea level for the areas plotted. Even the general public, not just amateur astronomers, might be interested in the spectacular grazing occultation of 3.7-mag. Electra, which will be visible with binoculars across Los Angeles and surrounding areas of southern California; you are encouraged to mention it to local media. I plan to lead an expedition for the Electra graze; let me know if you might be interested in joining it (see the bottom of this page for my contact information). If suitable sites can be found and the weather forecast is good, the graze will be observed from northern Orange County. But better sites with possibly better weather prospects exist farther east, such as north of Temecula near I-15; Borrego Valley; and farther east, the southern Imperial Valley west and south of Brawley. Some other observers will probably be trying to observe the graze from locations farther west, especially from the area northeast of Camarillo, but also possibly from Thousand Oaks, s.w. of Santa Paula, north of Solvang, and south of Santa Maria. See below about current weather prospects, plans, and detailed maps. Kiwi Geoff has developed a way to plot two offset lines to deliminate the multiple events grazing occultation zone for the Feb. 6th graze of Electra on his Google maps interactive Web site. He writes: "You can place two independant lines with respect the limit line, using positive values for NORTH of the limit line, and negative values for SOUTH of the limit line. So with ELECTRA, both offset values will be negative." Later, Charlie Ridgway hopes to be able to use Geoff's code to have this capability for the other Pleiades grazes, but a copyright issue needs to be resolved first. For the individual grazes, it's better to use Charlie Ridgway's general Pleiades graze page and click on the link for the graze for Then you can see the plot with an offset distance in km that you can specify. Also on the page for each event, below the map, is the table of WinOccult predictions (in a zipped Word file) for the event; you can use it to tell the U.T. of central graze at your longitude, as well as the altitude and azimuth of the Moon, and other information. As mentioned above, for the Electra graze, the height above sea level should be multiplied by 0.40 and the path shifted south by that amount; some maps with that shift already applied have been posted but if you create your own plots, you need to take this into account. The other grazes will have similar shifts, slightly larger for areas farther north, due to height above sea level, but note that the maps in the Word files on this Web site, and those on Derek Breit's Web site, already have the height above sea level taken into account for the areas shown using an average elevation for the flat areas depicted. The Electra graze occurs in a low area of the Moon so that the graze zone is 0.9 km to 1.9 km south of the northern limit line (after correction for height above sea level) for longitudes west of 117 deg. W. (Pacific coast to I-15 area near Temecula), and is 1.0 km to 2.0 km south of the northern limit east of the Temecula area. For all the other northern-limit grazes, the graze zone is less well-defined by previous observations (so new observations will be even more valuable), and is expected to be 0.5 to 2.0 kilometers south of the height-corrected northern limits for them. IF YOU OBSERVE FROM THE NORTHERN LIMIT LINE ITSELF, YOU WILL HAVE NO OCCULTATION (A MISS). Derek Breit has plotted maps of the graze paths for Alcyone across southwestern Oregon; of Pleione over the Cresswell, Oregon area; of 24 Tauri over northern California, and east of Reno, Nevada; and of 8.2-mag. SAO 76191 passing over Woodland and Sacramento, Calif. (this one is not on Charlie Ridgway's Web site) that you can see on his Web site. He hopes to try to observe the SAO 76191 graze himself, while observers in Oregon will be trying the Pleione and Alcyone grazes there (for Alcyone, click here for details and contact information for an expedition in southwestern Oregon being organized by Chris Stephan). For saving and printing the maps on Charlie Ridgway's Web site, for both asteroidal occultations and grazes, I've found (as advised by James Thompson) that an effective way to do it is, once you have maneuvered and zoomed in to the map area you want, hit the "prt sc" (print screen) key. That saves your screen into memory that you can then paste into a Word or Power Point file. But first you might want to paste it into a utility like Microsoft Paint where you can crop the image to include only the map area, and then paste that into the Word or Power Point file. The graze of 9 Tauri, visible along a path from northern Baja California to Louisiana and the only southern-limit graze, actually occurs a few hours before the Pleiades passage but is included since it occurs the same night. But unlike all the other grazes, it occurs near the Moon's South Pole (southern-limit) so its predicted profile is much different from those for the northern- limit grazes discussed above. So far, I know of no expeditions planned for this graze, but if any are planned, I can provide an estimate of where the multiple-events graze zone is relative to the southern limit line. The grazes are listed below; there are some other grazes of 8th- mag. stars that won't be as easy, but predictions can be made available for them, too. R west Approximate ZC# mag. # Lim U.T. path location Star name 521 6.7 30 S 2:36 n. Baja Calif. - Louisiana 9 Tauri s. of Tucson, AZ; between Las Cruces, NM & El Paso, TX; near Abilene & about 50 miles s. of Dallas/Ft. Worth, TX 537 3.7 31 N 8:01 s.Calif.(see above)-nMexico Electra = 17 Tauri 545 4.1 32 N 8:21 Cen.&s.e.Brit.Col.; Montana Merope = 23 Tauri from Glacier Park to n.e. Wyoming; near Rapid City, SD (low) 549 6.3 33 N 9:03 near Crescent City & Redding 24 Tauri Calif.; Fallon, NV; St. George, UT (low) 551 7.4 -- N 8:46 about 250 km n.e. of Edmonton, AB; near Saskatoon, SK & n. of Regina (low) 552 2.9 34 N 9:06 s.w. Oregon (see Breit's Alcyone = eta Tauri Web site above) to Monument Valley, AZ (low) 560 3.6 35 N 9:37 s.cen. Brit.Col.; Bonners Atlas = 27 Tauri Ferry, ID; near Helena & Bozeman, Montana (low) 561 5.0 36 N 9:47 Oregon - s. of Eugene to Pleione = 28 Tauri n. of Lakeview - see Breit's Web site The first column gives the star's Zodiacal Catalog number. The 3rd column, "R#", is the number of the graze line on the lower map on p. 164 of the 2006 RASC Observer's Handbook. "Lim" tells whether the graze is a northern-limit or southern-limit graze (all except the first one, ZC 521, are northern limits). "west U.T." gives the Universal Time of 2006 Feb. 6 at the western end of the path, usually near the Pacific coast; the time is always later farther east. Note that the times are of central graze; the graze will last 2 - 4 minutes, so observers should start watching 2 to 3 minutes before the central graze time for their area. MY EXPEDITION PLAN - NORTHEAST ORANGE COUNTY PRIMARY WITH NEAR TEMECULA FOR BACKUP Using KiwiGeoff's above site, I've plotted the path in detail over southeastern Villa Park, and southeast of there into the foothills of the Santa Ana Mountains, in northeastern Orange County, California, where I plan to lead an expedition to observe this spectacular graze. I can plot similar maps for others who might want to used other sites. A discussion of possible sites is below, but first I will mention the weather forecast and other possibilities. The current Accuweather is now forecasting mostly clear skies across southern California, with only scattered cirrus in most areas, 44% at Camarillo to 30% in n.e. Orange County. Accuweather curiously shows more thin clouds in the desert, 50%, and worse conditions to the west, with 79% mid-level clouds for Santa Maria. If this forecast holds, I'll try to stick with plans to observe from northeastern Orange County as described below, but if all of those sites have insurmountable problems, I'll switch to the better areas east of Temecula. We can't make decisions on the basis of the current mid-range forecast, which could be wrong; the Astro Meteo (Clear Sky clock) forecast that will be available Saturday morning will give a better idea of what the pattern of cloudiness is likely to be. At that point, when I'll be at my mother's place in Los Alamitos, I'll make a first decision about which area of southern California to select for trying to observe the graze. If northeastern Orange County doesn't look hopeless then, and has about equal or better prospects relative to other sites, I'll make a scouting trip to decide which of the posibilities that I describe below will be used. I will have e-mail access, but I will NOT be able to update my Web site; in order to learn my weekend decisions about the expedition, let me know an e-mail address where you can be reached over the weekend, if I don't already have it, or provide a phone number where you can be reached. I've already received that from a few of you. Of course, the parts of Los Angeles and most of northern Orange County traversed by this graze path are densely populated with only a few schools and parks that might provide suitable sites, but only at a few points, not in a fairly continuous line across the graze zone. While those who live within the path, or know of individual safe sites, are encouraged to try to observe the graze there, the rest of us should make an expedition to an area that is reasonably safe and with good access, with parking, across the 1-km-wide (0.6 mile wide) graze zone. As I see it, within Orange County these exit only in the foothills of the Santa Ana Mountains in the northeastern part of the county. I have produced an 11-megabyte Word file that shows maps and satellite images of the path crossing this area in detail; There is a similar one with details of back-up sites east of Temecula, 1.4 megabytes. You can see even more detail of this area at http://local.live.com as suggested by Ernie Iverson; with it, I hardly need to visit the area, especially with the birds-eye view you can even see the gate that will block access to Peters Canyon Reservoir, trees that will limit visibility at Silverado Elementary School, etc. In northeastern Orange County, I would prefer to observe as far west as practical, with first choice around Peters Canyon Reservoir which seems to be in Villa Park. Peters Canyon Road on the east side of the reservoir looks almost ideal, crossing the whole path, but Ted Fay, who has some familiarity with the region, thinks that access to that road may be blocked. The next possible sites might be along the Blue Diamond Roads and Shoestring Rd. south of Irvine Lake, but access to them is uncertain until they are visited; hills might obstruct the view to the west from some or most of those roads, which seem to be in valleys. Perhaps the best sites are on Irvine Mesa east of the Silverado Elementary School on Santiago Canyon Rd.; Irvine Mesa Road and the Silverado Truck Trail cross most of the graze zone, but those roads might not be navigable with an ordinary car, even if access to the area is not blocked. Finally, the school is in the middle of the graze zone, and other sites might be found along Santiago Canyon Rd. and some adjacent roads to cover the path, but from the school and south of it, hills to the west might block the view. Ted Fay notes that Irvine Mesa Rd. just north of the school is used as a star party site; if others have experience or suggestions about the areas described above, let me know. Wherever we decide to meet, I would like to meet at 10:30 pm to give ample time to find suitable locations for all observers and to set up equipment. For Peters Canyon Reservoir, we could meet at the intersection of Peters Canyon Rd. and Jamboree Rd. Other possible meeting places would be the intersection of Blue Diamond Haul Rd. and County Hwy. S18 (which is or becomes Santiago Canyon Rd.) or the parking lot of the Siverado Elementary school. Alternative sites east of Temecula would probably use sites along Pauba Rd. north of Route 79, extending north and south of Los Caballos Rd. That area looks wide open, but if there are any problems, alternate sites along De Portola Rd. and Anza Rd. east and north, respectively, of their intersection look good as well. EXPEDITION NORTH OF CAMARILLO Gary Goodman, email goodman@ez2.net , plans to lead an effort to observe near the small town of Somis a few miles northeast of Camarillo, from a school in the middle of the graze zone just east of Somis Rd. a few tenths of a mile south of E. Los Angeles Ave. (Route 118). This 1.4-megabyte Word file shows the graze zone in that area. David Dunham, IOTA home dunham@starpower.net 301-474-4722 cell 301-526-5590 office david.dunham@jhuapl.edu 240-228-5609 On February 4 and 5, I'll be in Los Alamitos, Calif., at 562-430-2391 & will have my cell phone above.