Previous Asteroidal Occultation Public Campaigns
by David W. Dunham
(dunham@starpower.net)
I know of three previous efforts to advertise occultations of bright stars by asteroids to the general public, to solicit their observations for possible scientific use. Of course, there have been many others that were well-publicized in the astronomical community (such as the occultation of kappa Geminorum by 433 Eros on 1975 January 24), but only three where the events were publicized in widespread non-astronomical newspapers and magazines. These three events were publicized in printed media since they took place before the internet became as wide-spread as it is now, and before cell phones and smart phones became ubiquitous. Also, the efforts suffered from generally inaccurate predictions since they occurred before accurate space astrometry results (ESA’s HIPPARCOS mission) became available in 1997. So it will be interesting to see how this year’s current effort for the occultation of Regulus by 163 Erigone, the first event that will be publicized with modern techniques, will compare with the previous 1983 May 29, occultation of 1 Vulpeculae by 2 Pallas. This remains the best-observed asteroidal occultation, with successful positive observations made from 130 stations in the southern USA and Mexico, and 117 negative observations (those who monitored the star from outside the path; besides the reporting observers, there were about 50 other observers at those locations who either also monitored the star, or assisted others who did that), as well as at least 250 observers in the predicted path who tried to observe the event, but who were clouded out. Details of the effort, and the results, are given in D. W. Dunham et al., Astronomical Journal, Vol. 99, No. 5, pp. 1636 – 1662, May 1990, available from http://articles.adsabs.harvard.edu//full/1990AJ…..99.1636D/0001636.000.html.
1983 May 29, occultation of 1 Vulpeculae by 2 Pallas
This remains the best-observed asteroidal occultation, with successful positive observations made from 130 stations in the southern USA and Mexico, and 117 negative observations (those who monitored the star from outside the path; besides the reporting observers, there were about 50 other observers at those locations who either also monitored the star, or assisted others who did that), as well as at least 250 observers in the predicted path who tried to observe the event, but who were clouded out. Details of the effort, and the results, are given in D. W. Dunham et al., Astronomical Journal, Vol. 99, No. 5, pp. 1636 – 1662, May 1990, available from http://articles.adsabs.harvard.edu//full/1990AJ…..99.1636D/0001636.000.html. Almost all of the observers were amateur astronomers; the star was magnitude 4.8 with a gibbous Moon, making it necessary to use at least binoculars to watch the occultation, so it was not a good event for public recruitment like the occultation of Regulus by 163 Erigone on March 20th. But about 7 of the observations were made from non-amateur astronomers from appeals for observations in popular science magazines, by Clark Chapman in The Planetary Report, and in Science News (material provided by D. Dunham). In addition, several of the hundreds of observers who spread across Texas, organized by Paul Maley, were not amateur astronomers strictly speaking, but included astronauts and others with a more general interest in science in general.
1984 March 4, occultation of sigma Scorpii by 241 Germania
In this case, the 3rd magnitude star could be seen without optical aid since moonlight did not interfere, and the star, being close to 1st Antares in an easily-recognized constellation (Scorpius) also helped. The predicted path was expected to cross China, but the path errors were many times the path width, due to the poor state of astrometry in general then (relative to now) and the inability of observatories to be able to make useable “last-minute” astrometric observations of the asteroid and star together, due to the huge difference between their magnitudes. Nevertheless, Wang Sichao, Purple Mountain Observatory, Nanjing, publicized the early morning event extensively in Chinese newspapers. Clouds prevented complete coverage of the wide zone where the occultation could have occurred. Over 3000 Chinese were able to monitor the star, dwarfing the 1983 Pallas effort in number of observers, but all of them had no occultation. I have not seen a publication of the results, but they were mentioned in my article, “Sigma Scorpii, a bright close binary” on p. 346 of Occultation Newsletter, Vol. 3, No. 6, June 1986.
1991 January 13, occultation of Alhena by 381 Myrrha
Until the occultation of Regulus by 166 Rhodope on 2005 October 19, this was the brightest asteroidal occultation ever observed; Alhena is gamma Geminorum, mag. 1.9. The path was expected to cross China and the southernmost part of Japan, so again, Wang Sichao at Purple Mountain Observatory in Nanjing, publicized the early Sunday evening event extensively in Chinese newspapers. This time, over 5000 people watched the star, setting a new record, and at least four of them in Shandong Province saw the occultation, while the rest had negative reports. This was reported in my abstract #54, “The Sizes and Shapes of (4) Vesta, (216) Kleopatra, and (381) Myrrha from occultations observed during January 1991” for the Asteroids, Comets, Meteors conference in June 1991 held in Flagstaff, Arizona (it’s online at http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1991LPICo.765…54D&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES ) and also in I. Sato, M. Sôma, and T. Hirose, “The Occultaiton of gamma Geminorum by the asteroid 381 Myrrha”, Astronomical Journal, Vol. 105, No. 4, pp. 1553 – 1561, April 1993, available from http://
articles.adsabs.harvard.edu//full/1993AJ….105.1553S/0001553.000.html but the reference to the Chinese effort is just “Dunham, D. W. 1991, private communication”. The occultation path shifted 700 km north of the expected tract, placing the actual path directly over Tokyo, one of the largest cities in the world. Apparently, almost 3 dozen observed the occultation; it was timed accurately enough for analysis at 18 locations, while about 15 others outside the actual path monitored the star, according to the Sato et al. A.J. article. The main efforts were made to secure observations from the southern part of Japan, where the event was expected, but it’s fortunate that the many amateur and professional astronomers in the Tokyo region watched, anyway, some without optical aid. It’s unfortunate that the path wasn’t predicted more accurately; since the chances for an occultation before the event seemed so low in Tokyo, the organizers did not want to commit to a public effort there that could have been spectacularly fruitful.
2005 October 19, occultation of Regulus by 166 Rhodope
There was no public campaign for this event. It is mentioned here only because it was the brightest star ever to be observed occulted by an asteroid, and remarkably, the star was Regulus, the same star that will be occulted by asteroid 163 Erigone (interesting that the numbers of the two asteroids differ by only 3) on March 20th of this year. Of course it’s extremely rare for the same star to be occulted by different sizeable asteroids in an interval of less than 10 years; if the March 20th occultation is observed, it will be the first time that we will have two asteroidal occultation observations of the same star. A public campaign in 2005 would have been complicated because the path crossed four different countries with different languages, Portugal, Spain, Italy, and Greece, and the path missed most of the larger cities, except Athens, where twilight was too bright to observe the event without a telescope. However the occultation was video recorded, by Derald Nye in southern Portugal and by David Dunham in southwestern Spain. You can look at Dunham’s YouTube video of the event to see what the March 20th occultation might look like, except that the motion of Rhodope across the sky was faster than Erigone’s will be. Therefore, the Erigone occultation will last longer for nearly all observers, and the gradual nature of the disappearance and reappearance of Regulus, due to the angular size of the star, will be more pronounced on March 20th. Unfortunately, in 2005 the weather was poor in southeastern Spain, where many mobile observers traveled, so altogether, there were only 12 observations of that occultation.