At about 4.7^h Universal Time on May 12, 2007, Pluto will occult the 13.3-magnitude star UCAC2 25822467 in a path passing over much of Antarctica and Patagonia. But in addition, Walker Vaning believes that rings of very small particles will also occult the star for observers in the whole hemisphere of Earth facing Pluto, which includes all of South and Central America, most of the Atlantic Ocean (including the Canary Islands), the Caribbean Sea, eastern Mexico, eastern USA, and eastern Canada. The star is at right ascension 17^h 53^m 32.0^s, declination –16° 22' 47" (equinox 2000.0).

Vaning thinks that occultations by the rings could occur even a few hours from the time of Pluto's closest approach to the star, so that observers in western Europe and southern Africa might try to record before sunrise, and those in western North America have a chance as soon as Pluto rises high enough for effective observation. Since the particles are small, there is a substantial wavelength dependence on the visibility; Vaning recommends observing in the blue, at as short a wavelength as possible. Vaning claims that he finds as many as 30 rings in the Kuiper Airborne Observatory blue observations of the 1988 occultation, but that the ring occultations are very shallow or absent in visual and red wavelengths.

LATE UPDATE: It turns out that the star to be occulted by the Pluto system tonight is binary. The main star (A) is a bit brighter than Pluto and the companion star (B) is perhaps a little fainter than Pluto. The B star is expected to be occulted by Hydra, the small outer satellite of Pluto, within a few minutes of 3:14 UT May 12th. More details are given by Bruno Sicardy here. Jean Lecacheux in France writes, "The duration in case of a central event could be between 2 and 7 seconds. The nominal path of the Hydra shadow is predicted above northern Africa, Gibraltar, and the Azores, but taking into account the large uncertainty and the morning twilight, the event has to be monitored southside from the Canaries, and northside from continental Spain and Portugal, the Baleares and south of France. This will be a very difficult observation, as the faint occulted star will be jammed between two brighter bodies, the main star A to the west and Pluto slowly approaching (at 2.85" per hour) from the east."

Pluto Occultations on July 31st and September 27th

David Herald predicts two more occultations of reasonably bright stars this year. On July 31, 2007, around 13.8^h UT, Pluto occults 13.3-magnitude UCAC2 25815762 at right ascension 17^h 45^m 42.0^s, declination –16° 29' 32". This event should be visible from much of Antarctica and probably New Zealand (the latter especially considering the north shift from Pluto's ephemeris that may have caused the north shift during the March occultation). During this event ring occultations are possible as seen from Australia, Indonesia, Philippines, Japan, Asia, and eastern Africa.

Then on September 27, 2007, around 14.8^h UT, Pluto passes extremely close to an 8.7-magnitude (!) star, SAO 160793. Earth will actually pass "between the shadows" of Pluto and Charon, with no occultation by either object visible from Earth's surface. But occultations by possible Plutonian rings might be observed from the night areas of most of Asia (from Arabia to Vietnam to western and southern China to the Ural Mountains), the Horn of Africa, western Australia, part of Antarctica, and the Indian Ocean. The star's UCAC2 position is 17^h 44^m 38.4^s, –16° 46' 35".

Note that these observations will be beyond the range of most amateurs; they involve obtaining continuous photometric tracings of the combined light of Pluto and the star that can be analyzed later for weak fluctuations due to rings.

Independent predictions and some graphics for these occultations, based on astrometric observations at Lowell Observatory, can be found at this MIT website. It also lists one more event (May 14th), but in that case the star is too faint for the confirmation of Plutonian rings.

Reporting Your Observations

For occultations of stars by small solar-system bodies, we have special report forms (.xls versions preferred, but plain-text forms are available as well) at these URLs:

• www.asteroidoccultation.com/observations/Forms/ AsteroidReportForms.html
• http://tinyurl.com/2xykpo

Once you complete one of these forms, please send it to IOTA's e-mail address reports@asteroidoccultat ion.com, which is also used for reporting asteroid-occultation observations.

Additional resources for reporting your observations are available at the website of the North American Asteroid Occultation Program:

• www.asteroidoccultation.com/observations/NA

Please check the online version of this AstroAlert on Sky & Telescope's website for possible minor updates:

• AstroAlert2007May11.html

Any major updates will be announced via subsequent AstroAlert messages. Good luck, and clear skies!