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Saturday, August 25, 2007

Astronomy: Viewing Vesta

If you've never seen an asteroid, the next few days present an excellent opportunity to remedy that lacuna. Asteroid 4 Vesta is the second most massive asteroid in the main belt, but, with a more reflective surface than dwarf planet 1 Ceres, is the brightest of the asteroids—in late May and early June Vesta reached magnitude 5.4 and was visible to the unaided eye in a dark and transparent sky.

It's faded now to magnitude 7.2, which is easily visible in binoculars or a small telescope, and over the next few days will be exceptionally easy to spot because it will be gliding past brilliant Jupiter in the southwest sky at dusk for observers in the northern hemisphere. On August 30th at 4h Universal Time, Vesta will be just 24 arc-minutes from Jupiter. If you aim your binoculars at Jupiter, you'll see Jupiter, its Galilean moons, the magnitude 4.6 star ω Ophiuchi, and Vesta within the five degree field of view typical for binoculars. This page (scroll down to “August 24–31”) provides day-by-day descriptions of the encounter for observers in the U.K., which are applicable for anywhere in the mid-latitudes of the northern hemisphere; the further south your latitude, the higher Jupiter will be in the sky and the more time you'll have before it sets.


Click image for an enlargement.

Around 22:00 local time (20:00 UTC), I easily spotted Vesta with the Vernonscope 80mm apochromatic refractor and a 40mm wide-angle eyepiece. The photo above was taken with a Nikon D200 digital SLR with an 18–200mm zoom lens at the maximum of 200mm (equivalent to a 300mm lens on a 24×36mm film camera) at f/5.6 with sensitivity set to ISO 1600. Exposure was 2 seconds, which is about as long as you can go at this focal length without noticeable star trails becoming evident. The camera was tripod mounted and the exposure was made with an electronic cable release in mirror lock-up mode to minimise vibration. Here is a computer rendering of this scene produced by the Your Sky virtual telescope.

If the weather co-operates (HAH!), I'll try to take photos each night throughout the conjunction and assemble an animation of the event. (2007-08-25 21:08 UTC)

Posted at August 25, 2007 13:58