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Vesta one of the largest asteroids reaches opposition on the 5th August 2011. Located in the constellation of Capricornus, Vesta will attain a maximum visual magnitude of 5.6, hence naked eye visibility for keen eyed observers from a dark site.

For surburbian observers and those who are not so lucky to have particularly dark skies, Vesta is still an easy binocular / small telescope object. So if you have never seen an asteroid before, now is an excellent time to do so.

Discovery

Vesta was the fourth asteroid to be discovered on the 29th March 1807 by the German astronomer Heinrich Wilhelm Olbers. Along with the other asteroids known at the time (Ceres, Pallas and Juno), Vesta was initially classified as a planet in its own right and subsequently was given its own planetary symbol. With further discoveries, all in the region between Mars and Jupiter, the general term asteroids was coined to describe them. Much later in 2006, the International Astronomical Union (IAU) defined a new classification of dwarf planet of which the largest asteroid Ceres is now a member.

Magnitude

Despite being only the third largest body in the main asteroid belt with a diameter of 530km (330 miles), Vesta is the brightest asteroid. It appears even brighter than the much larger dwarf planet Ceres and asteroid Pallas, which is slightly larger. This is because its approaches closer to the Earth than the other two and additionally has a much higher reflective surface. At favourable oppositions, the maximum visual magnitude of Vesta is 5.1 and therefore easily within naked eye visibility, especially from a dark site.

For opposition this year, Vesta will peak at mag 5.6.

Location

The second faintest constellation of the zodiac Capricornus provides the backdrop for this opposition. Capricornus is located at a declination of about -20 south and therefore never rises particular high in the sky for Northern hemisphere observers. Hence the best views of Vesta are seen from the Southern hemisphere, however for all observers the opportunity exists for a short time, to glimpse with the naked eye the only asteroid that is bright enough to do so.

Vesta - August 2011

Vesta - August 2011 - pdf format

One method to find Capricornus is to first locate 1st mag. Altair the brightest star in Aquila. There are two easily visible stars close to Aquila. About 2 degrees to the NW of Aquila is mag 2.7 Tarazed (γ Aql) and 3 degrees to the SE of Aquila is Alshain (β Aql) at mag. 3.7. Imaging a line connecting all 3 stars together and extend the line south for about 30 degrees. This will lead to the heart of Capricornus. Directly west of Capricornus is the famous Teapot asterism of Sagittarius. During the month of August Vesta moves steadily through the centre region of Capricornus and at month's end it makes a close approach to mag. 4.1 star ψ (psi) Capricorni.

Vesta Position Table

Date Time (UT) RA (J2000) DEC (J2000) Visual Mag. Constellation
Aug-01-2011 00:00 21h 11m 41.92s -22d 28m 34.3s 5.67 Capricornus
Aug-03-2011 00:00 21h 09m 49.64s -22d 44m 23.1s 5.64 Capricornus
Aug-05-2011 00:00 21h 07m 56.12s -22d 59m 49.9s 5.63 Capricornus
Aug-07-2011 00:00 21h 06m 02.09s -23d 14m 50.6s 5.65 Capricornus
Aug-09-2011 00:00 21h 04m 08.26s -23d 29m 21.5s 5.68 Capricornus
Aug-11-2011 00:00 21h 02m 15.29s -23d 43m 19.2s 5.72 Capricornus
Aug-13-2011 00:00 21h 00m 23.86s -23d 56m 40.6s 5.77 Capricornus
Aug-15-2011 00:00 20h 58m 34.61s -24d 09m 23.1s 5.82 Capricornus
Aug-17-2011 00:00 20h 56m 48.18s -24d 21m 24.3s 5.87 Capricornus
Aug-19-2011 00:00 20h 55m 05.15s -24d 32m 42.2s 5.92 Capricornus
Aug-21-2011 00:00 20h 53m 26.12s -24d 43m 15.1s 5.97 Capricornus
Aug-23-2011 00:00 20h 51m 51.65s -24d 53m 01.5s 6.02 Capricornus
Aug-25-2011 00:00 20h 50m 22.26s -25d 02m 00.4s 6.07 Capricornus
Aug-27-2011 00:00 20h 48m 58.45s -25d 10m 10.9s 6.11 Capricornus
Aug-29-2011 00:00 20h 47m 40.68s -25d 17m 32.6s 6.16 Capricornus
Aug-31-2011 00:00 20h 46m 29.36s -25d 24m 05.3s 6.21 Capricornus

Dawn

The Dawn spacecraft was launched on the 27th September 2007 on a mission to first study Vesta and then Ceres. Leaving Earth at a speed of 41,000 km/h (25,600 miles/h) and following a flyby of Mars, Dawn entered orbit around Vesta on the 16th July 2011. It will remain in orbit for about a year to map the surface and conduct scientific experiments before firing its ion thrusters and heading off towards a 2015 rendezvous and subsequent orbit around Ceres.

The spacecraft has already sent back some fantastic photos of Vesta and a couple of them are shown below:

Dawn image of Vesta from 5200km on 24th July 2011 (NASA/JPL Caltech/UCLA/MPS/DLR/IDA)

Dawn image of Snowman Craters on Vesta from 5200km on 24th July 2011 (NASA/JPL Caltech/UCLA/MPS/DLR/IDA)