Occultation snd Spectacular Graze of Spica, 2024 November 27 - Updated 2024 November 24
by David W. Dunham, Eberhard Riedel and Derek Breit
Google Earth files added for Eunice, NM; and for Midland, Brady, Rockdale, & Brenham TX areas, and Links to Google Maps added for the elevations of most of these areas
______________________________________________________ THE TOTAL OCCULTATION will be visible across much of North America except the west coast regions, as shown in the region of visibility map at the top of Rob Robinson's prediction page for the event that also has the predicted Universal Times and circumstances for the bright-side disappearance for hundreds of cities in Canada (CA), the USA (US), and several other countries, followed by a similar list for the more prominent reappearance, and concluded with a list of the coordinates of the cities. Unfortunately, most areas of the USA and Canada will likely contend with extensive cloudiness, as shown in this USA cloud cover forecast of Nov. 24, 0h UT. But less cloud is expected over parts of the graze path across Texas; see below for more about that. ______________________________________________________ SPECTACULAR GRAZING OCCULTATION OF SPICA, NOV. 27 AM, S. N.MEX. AND ACROSS TEXAS This great graze on the dark side of a 13% sunlit Moon is the best in North America this year, so we are planning an expedition to the graze path, shown on pages 173 and 174 of the RASC Observer's Handbook for 2024, and also on pages 1 and 2 of this IOTA grazes paper. This plain text file gives the Universal Time of central graze, and the circumstances (esp. the altitudes of Spica and the Sun) at 0.25 degree intervals of longitude along the path from N. Mex. to the TX coast. The profile lines up best near long. 107 W in New Mexico, but very clear skies will be needed to see it since the altitude above the horizon there will be only 3 deg. The profile will still give at least 4 occulta- tions where conditions are better n. of Austin, TX or over the northern Houston area. Links to Google maps of the graze path for different elevations above sea level are posted after the Google Earth section. Parallel offset lines can be specified with the Google maps to specify the better multiple events zones that you can then zoom in on to select observing sites. The last section has current cloud cover prediction maps. When you observe the graze, Spica will appear to pass over the southern cusp of the Moon a few to several minutes before central graze; the duration of the graze depends on your distance from the predicted (elevation-corrected) limit and can be estimated from the predicted profile. __________ GOOGLE EARTH FILES GENERATED WITH GRAZPRED IOTA/European Section's Eberhard Riedel has generated several Google Earth (GE) files that will allow observers to select observation sites in narrow bands where the predicted lunar profile shows the maximum number of occultations of the star during the graze can be observed. Thanks to the detailed lunar topographic information derived from NASA's Lunar Reconnaisance Orbiter (LRO), these predictions are quite accurate, much more so than before the early 2000's when we had to rely on Watts charts. Riedel has used his GRAZPREP software to project the lunar profile on the surface of the Earth so that, for any location in the graze zone, you can predict how many occultations of the star will occur. Riedel wants others to use GRAZPREP; his description gives more information about how it can be done and its advantages as a modern graze prediction software package. Besides the GE files showing the whole profile, there are other GE files that show just the narrow bands where the msximum number of occultations (or contacts, with D and R, twice the number of occultations) will occur; they are shown as blue lines, with thicker yellow bars showing just the part of the lunar profile that will cause the occultations. A white line shows the "smooth (spherical) Moon" southern limit line for the whole occultation, with thicker white bars showing the part of the lunar profile that will occult the star there, usually fewer times than along the blue lines. This .zip file contains GE files for the graze path over three regions [clicking on them shows an overview map showing the best band(s) with the most predicted contacts]: I-25 and NM Hwy 1 27 miles north of Truth or Consequences, NM (Long. 107 W) north of Austin, TX (between Georgetown and Jarrell, Long. 97.6 W) northern side of Houston, TX (Long. 95 W) This shows the whole profile ("all lines each 50m") for part of Houston. This .zip file contains GE files for the graze path over THREE MORE regions [clicking on them shows an overview map showing the best band(s) with the most predicted contacts]: Eunice, NM Hwy 18 over NM Hwy 18 + s. of NM234 and TX176 (Long. 103 W) n. and e. of Midland, TX over I-20 and TX Hwy 349 (Long. 102 W) north of Brady, TX, over US 277 and 283, and TX300 (Long. 99 W) This .zip file contains GE files for the graze path over the San Angelo, TX region [clicking on it shows an overview map showing the best band(s) with the most predicted contacts]: n. and n.e. of San Angelo, TX over TX Hwy 208, US 277, & US 67 (Long. 100.2-.7 W, 4 GE files) This .zip file contains GE files for the graze path over TWO MORE regions [clicking on them shows an overview map showing the best band(s) with the most predicted contacts]: s. of Rockdale, TX over US 77 (Long. 96.8-97.1 W) n. & e. of Brenham, TX over TX Hwys 50 and 105 (Long. 96.2-96.5 W) They were listed from west to east, since that's the direction the lunar shadow will move, but they're now out of that order, since they have arrived at different times as we've seen the need to cover more areas. So I list them again below, in west to east longitude order, and giving at the end, the number of the .zip file that includes the GE files for each: I-25 and NM Hwy 1 27 miles north of Truth or Consequences, NM (Long. 107 W) - zip1 Eunice, NM Hwy 18 over NM Hwy 18 + s. of NM234 and TX176 (Long. 103 W) - zip2 n. and e. of Midland, TX over I-20 and TX Hwy 349 (Long. 102 W) - zip2 n. and n.e. of San Angelo, TX over TX Hwy 208, US 277, & US 67 (Long. 100.2-.7 W, 4 GE files) - zip4 north of Brady, TX, over US 277 and 283, and TX300 (Long. 99 W) - zip2 north of Austin, TX (between Georgetown and Jarrell, Long. 97.6 W) - zip1 s. of Rockdale, TX over US 77 (Long. 96.8-97.1 W) - zip3 n. & e. of Brenham, TX over TX Hwys 50 and 105 (Long. 96.2-96.5 W) - zip3 northern side of Houston, TX (Long. 95 W) - zip1 This shows the whole profile ("all lines each 50m") for part of Houston - zip1 The first region, near I-25 in New Mexico, has the most predicted contacts, 14 (or 7 occultations), but Spica will be only 3 deg. above the eastern horizon at the time, so very clear skies will be needed to see the graze there. Of course, I-25 is not suitable for observing sites, but observing sites can be found along NM Highway 1 a mile west of the Interstate. The best zone, which is 500m south of the white smooth-Moon southern limit, intersects NM Hwy 1 at latitude 33 deg 28' 41.6" N, longitude 107 deg. 14' 43.7" W. The GE files that you get from unzipping the .zip file (save them to a directory that you might name "Spica graze" on your computer), have long names including the central longitude for which they are valid and the elevation above sea level (in meters) and whether they show "all lines" or just the best band(s) as "X contacts" where "X" is the maximum # of contacts. You should just use the "X contacts" file for finding observing sites in your selected area. The "ZC 1925" in the name refers to the Zodiacal Catalog number of Spica. When you use Google Earth, when you zoom in on an observing site, you can toggle the line with the yellow bars off (or on) by clicking on the box shown in this screen view; that will allow you to see your site that might otherwise be covered by the yellow bar. __________ GOOGLE MAP PAGES GENERATED WITH OCCULT4 These have been posted by Derek Breit, but we found that if we provide hot links to them, the old Java script doesn't work and you can't plot parallel offset lines, the main advantage of using the Google maps. Therefore, we provide the link URL's, but not as hot links. You need highlight and copy the link, then paste it into your Web browser; the Google map should then work, with the dark grey parallel offset lines that you specify in the two boxes above the map. To get values (in km) for the offsets, consult the predicted profile (links to them are given) to get the distances of the edges of the band you want to show. Note that the values you specify are negative north of the predicted limit line, and positive for south of it, as labelled on the vertical axis of the profile. Number of events are indicated as grey bars on the left side of the profile; the farther to the right it extends at a given distance, the more contacts will occur; just measure the top and bottom of the bar that extends farthest to the righr. That can be done more accurately if you have Occultr on your computer and generate the profile yourself, since then clicking anywhere on it gives the values. Below I list the longitude (clicking on it shows the predicted profile for that area), the U.T. and circumstances of central graze, the elevation above sealevel of the area, Derek's Google map link, and a description of the region (for more description, see the above Google Earth section for the corresponding longitude/area). Altitude (alt.) above the horizon is in degrees. elev. west U.T. Spic above Long. h m alt. sealevel Google map URL (link) Valid area 107.2 10:53.8 3 1600m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_1600m.htm NM Hwy1 - I-25 n. of Truth or Conseq., NM 103.0 10:55.0 7 1000m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_1000m.htm Eunice, NM area 102.0 10:55.3 8 820m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_820m.htm n. and e. of Midland, TX 100.4 10:56.0 10 670m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_670m.htm n. and n.e. of San Angelo, TX 99.3 10:56.6 11 500m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_500m.htm n. and n.e. of Brady, TX 97.5 10:57.6 13 250m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_250m.htm n. of Austin, TX 95.5 10:58.8 15 25m http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_25m.htm n. side of Houston, TX __________ CLOUD COVER FORECAST OF NOV. 24 AT 12h U.T. Unfortunately, the outlook is poor for New Mexico, especially the Rio Grande valley around I-25 north of Truth or Consequences, where the profile lines up the best, so we plan instead to travel to central Texas to observe probably in the Brady area. Although some clouds are expected in both the Houston and Austin areas, it looks like the region between them may be mostly clear, but the latest models disagree for the Austin region, GFS says it will be clear there, but the other models say it'll be cloudy, and better farther east. GFS New Mexico and Texas forecast of Nov. 24, 12h UT (I believe this is the best forecast) ECMWF New Mexico and Texas forecast of Nov. 24, 12h UT NWS New Mexico forecast of Nov. 24, 6h UT (give up on this, not further updated) NWS Texas forecast of Nov. 24, 18h UT (has coverage to cen. New Mex.) ________________________________________________________ NOVEMBER 27TH SPICA NORTHERN-LIMIT GRAZE ACROSS EASTERN CANADA Although the southern-limit graze described above is by far the best, the northern-limit bright-side graze visible from eastern Canada might be seen with small telescopes. The graze is in a dark sky in the northern part of the path over northern Quebec, but is in brightening dawn twilight as the shadow moves south over Labrador, and will occur shortly after sunrise when it crosses northern and southeastern Newfoundland. This plain text file gives the Universal Time of central graze, and the circumstances (esp. the altitudes of Spica and the Sun) at 0.25-degree intervals of longitude along the path. The predicted profile at longitude 53 deg. west (for the area southwest of St. John's) shows that the best place to observe the graze should be about 0.77 km southwest of the southern limit line where 9 or more occultations of Spica could occur. Since the graze will be on the bright side of the Moon, the contacts are unlikely to be visible to the naked eye, but they might be seen with binoculars, and will certainly be seen with any small telescope, if the sky is clear. If you plan to try to observe this northern-limit graze, please let David Dunham and Eberhard Riedel (email E_Riedel@msn.com) know (specify the longitude and latitude of your intended observation area, to a few minutes of arc accuracy) and we can send you appropriate Google Earth files (like the ones described for the s. limit above) to cover that area. Unfortunately, the current cloud cover prediction for the area is very poor, likely totally overcast. In case anyone wants to try, Derek Breit has posted a Google map for the northern limit graze at: http://www.poyntsource.com/New/Google/ZC1925_2024_Nov_27_North_25m.htm ________________________________________________________ Maps and lists for 142 of the best lunar grazing occultations across N. America during 2024 (18 in the future) are given on this IOTA grazing occultations page. ________________________________________________________ David Dunham, dunham@starpower.net Eberhard Riedel, E_Riedel@msn.com Derek Breit, breit_ideas@poyntsource.com