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Thursday, April 27, 2017


The Moon Occults Regulus (4 May 2017)

The northern horizon as seen from Adelaide at 18:17 ACDST Thursday 4 May, the bright star Regulus is close to the Moon an hour before it is occulted. Similar views will be seen elsewhere in Australia at the equivalent local time, see the table below. Click to embiggen.The Moon and Regulus at 19:24 ACST  Thursday 4 May just before the Moon covers Regulus.Click to embiggen.

On the early evening of Thursday 4 May the bright star Regulus is occulted by the Moon as seen from the most of Australia. This is the second of two occultations of Regulus, the brightest star in the constellation of Leo the lion, this year. The previous one was in February, and images can de seen here.

The Moon is a very obvious signpost for where to look and Regulus will be the brightest object near the Moon. Start watching about half an hour before the occultation (see table of times below) to get set up and become familiar with the sky. Although this event is easily seen with the unaided eye, given the brightness of the Moon the occultation is best seen  in a small telescope or binoculars.

Regulus will appear to "wink out" as it goes behind the dark limb of the Moon, at just past first quarter, the dark edge of the Moon will be sufficiently dark for the disappearance to be dramatic, although seeing the edge will be difficult. Reappearance on the bright limb will be harder to see as you have to be looking just at the right moment.

Reappearance as seen from Hobart at 21:19 AEST.Reappearance as seen from Brisbane at 21:36 AEST. Note the difference in location where Regulus reappears.

The occultation occurs in the early evening, a good time to get the kids involved (although maybe a littel close to dinner time), the Moon will be reasonably high above the northern horizon. The Moon is easily visible and a ready signpost to Regulus.

If using a telescope, it is advisable to set up and practise on the Moon a day or so before the event, so you are familiar with your telescope set-up. Set up at least half an hour ahead of time so that you can be sure everything is working well and you can watch the entire event comfortably (trying to focus your telescope moments before the occultation will cause a lot of unnecessary stress).

Regulus will be clearly visible with the unaided eye, binoculars or in a telescope near the Moon before the occultation. Here's some images from the occultation of Regulus back in February, so you know what to expect.However, the first quarter Moon will not be as bright as the nearly full Moon, so photography will be easier.

PlaceDisappears Bright Limb Reappears Dark Limb
Adelaide ACST19:2420:39
Brisbane AEST20:1421:36
Canberra AEST20:1121:31
Darwin ACST18:3320:05
Hobart AEST20:1921:19
Melbourne AEST20:0921:21
Perth AWST-18:01
Sydney AEST20:1421:35

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