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Viewing Vesta
Viewing Vesta

Have you ever seen an asteroid? No, not one in a computer game, but one of the thousands of small bodies orbiting the Sun between the orbits of Mars and Jupiter. This month will be a great opportunity to see one.

The first asteroid Ceres (reclassified as a Dwarf Planet in 2006) was discovered by Giuseppe Piazzi on January 1, 1801, the first day of the 19th century; at 957 km in diameter it is the largest asteroid. Vesta was the fourth asteroid discovered six years later in 1807 by Heinrich Wilhelm Olbers. Although at 512 km diameter only half the size of Ceres, it is significantly brighter because of its unusually bright surface material, making it by far the brightest asteroid, the only one visible (barely) to the naked eye.

This month Vesta will be located in the constellation Ophiuchus, roughly 10 degrees northwest of Jupiter. It begins the month at magnitude 5.4, located half way between the 2nd magnitude stars Sabik and Han (Eta and Zeta Ophiuchi), gradually brightening to magnitude 5.2 and moving westward, ending the month about half way between Han and Phi Ophiuchi. This will place it exactly 1 degree south of the bright globular cluster Messier 107, making an interesting pairing in any telescope. When near opposition on May 30, it will be moving almost a quarter of a degree each day, so plotting its position relative to surrounding stars on successive nights will make its identification very easy.

Under clear dark skies, the human eye can see down to about 6th magnitude, so that Vesta should be just detectable with the naked eye in May and June. Any sort of optical power, such as a small binocular, will make it easy to see and identify. Use Starry NightŪ to plot its position from night to night to help in finding it. Here, for example, is a plot of the objects discussed for May 30:

May 2007

Geoff has been a life-long telescope addict, and is active in many areas of visual observation; he is a moderator of the Yahoo "Talking Telescopes" group.

Date Taken: 06/02/2011
Author: Geoff Gaherty
Category: Archives

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