Jupiter at Opposition - May 4, 2006

Dia 1:The sky looking south at midnight (01h 00m BST) on May 4 2006.
Fig 1:  Jupiter in Libra. A photograph looking south April 19 2006 at 01h UT. A 2 minute exposure, 36mm f/2.8 ISO 400.
Fig.  2    Jupiter in Libra. A photograph looking south April 27 2006 at 23h 30m UT. A 2 minute exposure, 36mm f/2.8 ISO 400.
Fig 3: Jupiter in Libra. A photograph looking south April 29 2006 at 23h  47m UT. A 2 minute exposure, 36mm f/2.8 ISO 400.
Fig. 4    Jupiter imaged May 01 at 23 58m UT. A 5 sec. exposure, 450mm f/4.5  ISO 400.    The stars alpha(1) & alpha(2) Libra are seen at the bottom of the photograph.
Fig. 5    Jupiter imaged May 01 at 23 58m UT. A 1/4 sec. exposure, 600mm f/6  ISO 400.

Jupiter has been a conspicuous object low down in the south-east of a late evening for several weeks now.

It comes to opposition on May 4th.

Jupiter is not well placed from high northern latitudes for telescopic work.

Its low altitude also appears to offset its apparent brightness when compared to the bright star Arcturus above (see Dia. 1), which it outshines tenfold.

The planet is presently retorgrading in the constellation Libra.

The motion is readily appreciated with reference to the star alpha(2) Libra (see Figs 1-3). This is quite discernible over the space of two days (Figs 2- 3). Note the light pollution from Kirkwall, particularly in Fig. 1.

Those interested in the motion of Jupiter's four large satellites may photograph them using modest equipment.

For example, using a 400mm (600mm 35mm camera effective) f/6 lens will capture the satellites digitally in a1/4 sec exposure or less. (See Fig. 5)

A tripod is essential and the shutter should be operated by cable release or time delay setting.

Even so, at this magnification, the diurnal motion will show in slightly elongated images which may be further distorted from the slightest camera shake.

The 5 second exposure shown in Fig. 4 was obtained with the camera attached to a motor driven equatorial mount.

The star alpha(2) Libra, magnitude 2.7, is somewhat confusing in its names and definitions.

It is in fact the brighter of two stars 230 arc seconds apart. The second star, magnitude 5.3, is designated alpha(1) Libra.

This is because it precedes the brighter star in Right Ascension. But, one might ask, why call it alpha at all? It might be understandable if the designation had been applied to the pair before they were known to be double.

However, at this separation (somewhat greater than the eye's resolution) and, despite the difference in brightness, the duplicity must have been known from pre-telescopic times.

For good measure the brighter alpha(2) is also known by a variety of names including Zubenelgenubi and Zubeneschamali.

But the latter is by general consent the name given to beta Libra (magnitude 2.6 and therefore brighter than alpha!) situated about 9 arc degrees above.

Libra, as most people will know, lies between the sprawling Virgin and the brilliant Scorpius.

It is, along with Pisces, the faintest of the Zodiacal constellations so that Jupiter's presence makes a valuable marker for those a little at sea in the region.

Jupiter continues to retrograde until July 4 after which forward motion is restored.

It completes another retrograde loop during late 2006 and throughout 2007 within the constellation Scorpius itself.

The planet will be in Sagittarius during 2008 after which northern observers may look forward to its gradual return to more favourable elevations.

JV 02.05/06