The Event

In the pre-dawn of June 23 (June 22 UT), the dwarf planet Pluto and its satellite Charon are expected to occult the 12th magnitude star 2UCAC 25370733 in Sagittarius as seen across a number of sites in Australia.  The event was included in Edwin Goffin's predictions issued in the circular CA 2007/4 and can be viewed here including a detailed finder chart.  Should an occultation occur due to any of the bodies in the Pluto system, the star will dim to the magnitude of Pluto giving a magnitude drop of about 2.1.  Video observers should be able to image the star with telescopes of 10 inches aperture or larger when using a non-integrating video camera - integrating cameras will allow imaging with smaller apertures.  Complicating the observations of this event is the fact that most eastern seaboard Australian observers will be monitoring the field at low altitude - generally less than 20 to 25 degrees and that there will be a waning gibbous moon higher in the sky.

Recent astrometry of both Pluto and the target star has allowed the predicted path to be updated.  Below are graphics showing the occultation paths for Pluto and Charon as developed by Dave Herald..

However, using different assumptions and ephemeredes, a number of other predicted paths have been generated and can be seen at the links given below.

Bruno Sicardy (Paris Observatory) recently updated prediction

MIT Prediction

Given the variation between these predictions, there is clearly a significant level of uncertainty about the amount of south eastern Australian that is likely to fall within the main occultation path of Pluto and the southern limit of the occultation path of Charon.  As such, this is a worthwhile event for any Australian observer with the equipment to allow the monitoring of this event.

Rings and Things

As was highlighted for the Pluto event in September 2007, this event offers the opportunity to detect any possible ring systems around Pluto.  Possible locations of rings could include within the orbit of Charon and close to Pluto or sharing the orbits of the outer moons Nix and Hydra.  Observers should be watching carefully for possible irregular fading of the target star lasting for several seconds around the expected times. Tabled below are the expected times for the orbits to cross the star as seen from the Australian region.  The latter events are unlikely to be observable from the East coast due to very low altitude and twilight.

Below are a number of graphics generated using Occult 4 showing the view THROUGH the Earth and Pluto system towards the target star showing the relative positions of the satellites at the times tabled above.  Interested observers can also download here the Element file for Occult 4 for this event.

Any observations of this event (either positive, negative or clouded out) should be sent as soon as possible after the event to Graham Blow or Steve Kerr.

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