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Jupiter occulted by the Moon down under
BY MARK ARMSTRONG
ASTRONOMY NOW

Posted: 1 October 2012


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Jup-occ-6-Oct-Perth_400x323 Observers in south-western Australia can witness a great astronomical event on the morning of 6 October when Jupiter, Ganymede, Io and Callisto are occulted by the Moon. This is the view at 4.50am WST as Jupiter is about to be occulted with Callisto waiting its turn. Graphic made using Guide 8 www.projectpluto.com

Observers in south-west Australia are in for a real treat on the morning of 6 October when a waning 73 percent illuminated gibbous moon totally occults the gas giant Jupiter and three of its Gallilean satellites. It will be fascinating to see Jupiter gradually move behind the lunar limb over the course of a few minutes. For observers in a small part of south eastern Australia there is a total occultation, with Hobart favoured and grazing events in Adelaide and Melbourne, but unfortunately the Sun is above the horizon.

The city of Perth will see the disappearance of Ganymede, Io, Jupiter and Callisto at the bright lunar limb (Europa is hidden behind Jupiter at the time of the occultation) and the reappearance too, although the Sun is just rising so making it more difficult to observe, although the Moon is still well up. For the reappearance it's important to know where at the Moon's edge Jupiter and its moons are predicted to reappear. Astronomers use a term called 'position angle' (PA) to describe the relative location of two bodies, most commonly doubles stars or in this case the lunar limb and Jupiter. One easy way of visualising PA is the Moon as a clock-face with north, east, south and west around its edge with a total of 360°, measured anti-clockwise from north. So if a star reappears at due north on the lunar limb the PA is 000°; due east, 090°; due south, 180° and due west, 270°. Jupiter and its moons will reappear at PA 323 to 326°, the north-western lunar quadrant.

Jup-occ-6-Oct-Perth-reappearance_400x305 Jupiter reappears at 5.52am, following Ganymede and Io minutes earlier. Callisto reappears at 6.12am but the Sun is up by then. Graphic made using Guide 8 www.projectpluto.com

This event can be viewed in binoculars but observing with a driven telescope where some magnification can be brought to bear is a much better option. Imagers should have a good time of it with perhaps some enterprising amateurs securing some video footage.

Astronomy Now would be delighted to receive any images or observing reports; send them to gallery2012 @ astronomynow.com

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