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Moon occults dwarf planet Ceres for North America

Posted: 8 September 2012

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Ceres Occultation This is the view of Ceres' reappearance form New York shortly after 4.18am EDT. The Moon is 46 degrees up.

Dwarf planet Ceres, the largest body in the Asteroid Belt, is occulted by a 42 percent illuminated Moon in the early hours of 9 September. The vast majority of Canada and the United States will be able to observe this event, apart from the far south of the US and the further east you are the easier the viewing will be, with the Moon higher in the sky.

Because of the Moon's glare and the comparative faintness of Ceres (magnitude +8.8) it will be difficult to observe the disappearance of Ceres at the bright lunar limb (and that event is not visible on the west coast) but the reappearance of the dwarf planet at the dark limb will be an easy observation for observers equipped with tripod-mounted big binoculars or small telescopes, as long as you are peering at the right place on the lunar limb for a Ceres' reappearance; it's important to know where at the moon's edge Ceres is 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 Ceres. 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°.

There will be a grazing occultation for observers along a narrow path running across central Texas, northern Louisiana, central Mississippi, northern Alabama, eastern Tennessee and finally Virginia. Those south of the line will miss out on an occultation all together with the lucky ones along the graze line and north of it for the total occultation.

All of the pertinent information, including timings, position angles and lunar altitude for many towns and cities across North America can be found at

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