Partial lunar eclipse 4 June
BY MARK ARMSTRONG
Posted: 3 June 2012
The path of the Moon through the penumbra and umbra. Graphic: Fred Espenak/NASA/GSFC.
The transit of Venus is not the only event taking place this month; a partial lunar eclipse takes place on 4 June (UT) and although it lacks the beauty of a copper-coloured moon at a total eclipse, there is still a very real fascination to be had from seeing a large chuck 'bitten out' of the Moon. As with all eclipses, only certain parts of the world are favoured to lesser or greater degrees, with large parts of the Earth missing out completely. Look out for it in much of the Americas, the Pacific, East Asia and Australia. The Earth's umbral (the central, darker part) shadow will reach 38 percent into the lunar disc at 11.03 UT, plunging much of the Moon's southern hemisphere into darkness. Before the main partial eclipse, the Moon enters the Earth penumbral shadow (the outer, much dimmer part), but the effect is very subtle.
Sky gazers on the Hawaiian Islands will be amongst the first to see the eclipse and all of it too, with the penumbral shadow making its subtle presence felt on 3 June at 10.48pm local time in Honolulu. The Moon will be 40 degrees up already, so from dark sites and, hopefully a transparent sky, something will be seen. The main event starts at midnight with mid partial eclipse at 1.04am. By just after 2am the Moon moves out of the umbral shadow and the whole thing ends at 3.18am.
A map of the Earth showing the regions of eclipse visibility. Graphic: Fred Espenak/NASA/GSFC.
Moving to mainland USA the further west you are the better but even on the west coast the Moon is less than 20 degrees up at mid eclipse and not much further east inland starts to sink into the mire prior to setting. Observers in Los Angeles and San Francisco will see the start of the penumbral eclipse at 1.46am local time, with the start of the partial eclipse at 3am. The Moon will only be 17 degrees up at mid eclipse just after 4am and about 45 minutes and seven degrees away from setting at the end of the partial phase at 5.06am.
From Phoenix the partial eclipse begins at 4am with the Moon 23 degrees up and will sink by a further 10 degrees up to mid eclipse time at 5.04am. The last part of the partial phase will be blighted by ever-increasing twilight and adverse altitude. At the time the partial phase ends at 6.06am the Moon is on the horizon and the Sun is almost up. Those observing from Denver can see the start of the partial phase at 4am but the Moon has sunk to an altitude of only six degrees and there is rapidly brightening skies by mid-eclipse at 5.04am. From Houston the start of the partial phase is marred by a lunar altitude of only 15 degrees and only a short time after that to witness it, but as far east as Chicago it will hard to see even a hint of the start of the penumbral stage at 3.46am, with the Moon almost having set by the time of the partial phase at 5am.
From Africa, Europe and most of Asia none of the eclipse is visible. Skywatchers in eastern Asia fair better; from Shanghai in China the eclipse is visible in less than ideal circumstances at moonrise, with the end of the partial phase occurring at 8.06pm local time, the Moon a mere 13 degrees up. Perhaps the very end penumbral phase at 9.20pm will be seen in favourable atmospheric conditions, the Moon having climbed to 25 degrees. Japanese observers in Tokyo fare slightly better with mid eclipse occurring at 8.04pm local time with the Moon 12 degrees up. As the eclipse progresses the Moon will gradually haul itself further clear of the sunrise east-south-east horizon, reaching a respectable 20 degrees by the end of the partial phase at 9.06pm.
Australia and New Zealand observers will have a great view of the eclipse, with the whole event visible east of Western Australia. In Perth the start of the partial phase will occur at 6pm in deepening twilight with the Moon eight degrees up, rising to 20 degrees by mid eclipse. Further east in Adelaide the beginning of the penumbral phase occurs at 6.18pm, coinciding with the dark getting properly dark but the Moon only 13 degrees up. Observing circumstances are much more favourable by mid-eclipse at 8.34pm, with the Moon riding high at an altitude of 40 degrees, and for the rest of the eclipse. Over on the east coast skywatchers can see all the eclipse with the luxury of the Moon above 20 degrees altitude and in astronomically dark skies. In Sydney the eclipse starts at 6.48pm with the Moon slipping into the Earth's dark umbral shadow at 7.30pm. Mid-eclipse is around 8.30pm with the Moon leaving Earth's dark, central shadow at around 9.30pm. In New Zealand the eclipse starts with the Moon already above 40 degrees altitude and by mid-eclipse time at around 11pm it will be 65 degrees up. The eclipse ends on 5 June at 1.20am local time.
This is the best lunar eclipse in 2012 and there won't another partial eclipse until April 2013 and an even longer wait until April 2014 for the next total lunar eclipse. So make the most of this event and if clear skies are forecast for your area, then try to take the opportunity to view one of astronomy's great show's. Astronomy Now would love to see your images; please send them to gallery2012 @ astronomynow.com