Finder chart for Pluto during 2007. Chart showing path of Pluto in 2007.

Positions Pluto in 2007.

Pluto was originally thought of as the smallest, and usually the outermost, of the major planets. With the discovery beyond Neptune of a number of other objects of the same sort of size, opinion swung to thinking of it as one of the larger Kuiper belt objects. Some of these, like Pluto, have a period in the raio 3:2 with Neptune.

At the August IAU meeting in Prague it was decided to reclassify the larger of these object, including Pluto, as Dwarf Planets. Whether the name will stick remains to be seen.

In 2007, Pluto's apparent path be just inside Sagittarius in its northwest corner close to Serpens and Ophiuchus. During 2007 Pluto will be remain in a lobe of the Milky Way with numerous background stars of a similar magnitude to the planet. This is likely to make its detection more difficult.

At present, Pluto has a magnitude about 14, so is likely to need a telescope aperture of 25 cm to see. Keen eyed observers viewing under good conditions from a dark site may be able to spot the planet with a smaller telescope. The planet is at opposition on June 19. Thus May, June and July will be the best time for attempting to view it. It is in conjunction with the Sun on December 21, so starts and ends the year too close to the Sun to observe.

The faintness of Pluto, magnitude 14 will make this a very difficult event to observe, especially as the full Moon will be only 14° away. In addition Pluto is a magnitude brighter than the star so the dimming at occultation will be only very slight.

Telescopes with an aperture of at least 30cm (12 inches) are likely to be necessary to actually view the event, but even then the dimming as Pluto moves in front of the star will be too slight for the human eye to detect.

An observer vieing through a sufficiently large telescope near the centre of the path may actually see a "central flash". This can occur when the observer, Pluto and star are exactly in line and Pluto's atmosphere acts as a refracting lens to brighten the light of the star.

Pluto is much smaller than the Earth with a diameter of only 2300 km. The shadow will cross the Earth in a band with the same width. It just happens the only major land mass it crosses is New Zealand, with the centre of the path crossing Canterbury University's Mt John observatory at about 4.23 am on the morning on June 13. Mt John is therefore the world's best placed observatory for viewing this event. Path of event

Such events are very rare. A previous Pluto occultation in 1988 was also visible from New Zealand and demonstrated for the first time the presence of an atmosphere on Pluto as the star's light rays were bent as they grazed past the planet.

A number of international teams will be soming to New Zealand to view this event. They will be using specialised electronic cameras, sensitive to the small changes in light level involved. At least two groups will be going to Mt John, one from Williams College, Massachusetts and another from the Paris Observatory at Meudon, France. Other groups will be observing from near Dunedin, from Carter Observatory in Wellington and from Auckland.

Further information, including some detailed sky photos and charts, can be found at the European IOTA web site.

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