In an earlier post I drew your attention to Venus and Mars in the evening sky at dusk. The pleasure derived from sighting the brightest planet, hanging like a small lantern above the horizon in the deepening twilight, is always enhanced by the proximity of the Moon. Fortunately, such a conjunction occurs on the evening of Saturday 3 December.
Observers in the UK will find Venus almost directly below the three-day-old Moon low in the south-southwest in deep twilight an hour after sunset on 3 December. Some 5½ degrees separates the two celestial bodies, so it will be difficult to fit the pair in the same field of view of most 10×50 binoculars, but 8x and 7x instruments will encompass them easily. In a telescope, Venus displays a gibbous 17.2-arcsecond-wide disc that requires a magnification of 105x to enlarge the planet to the same angular size as the Moon appears to the unaided eye.
The view from America
Five or more hours west of the British Isles, as evening twilight deepens on the eastern seaboard of North America on 3 December, the angular separation of Venus and the (by now) four-day-old Moon has increased to 7 degrees and the Moon will have slipped over the constellation border into Capricornus. Look in the southwest an hour after sunset.
On the US west coast, if you wish to see the crescent Moon and Venus at their closest, you should look in the southwest an hour after sunset on the evening of 2 December. The pair lie 7 degrees apart as seen from Los Angeles an hour after sunset on this date, whereas they are 8 degrees apart on the evening of 3 December.
The Antipodean view
In Australasia, observers should look to the west an hour after sunset on 3 December to see the waxing crescent Moon 6 degrees to the lower right of Venus. If the west-southwest aspect of your Antipodean sky is particularly clear and unobstructed, you may be fortunate to also see innermost planet Mercury (magnitude -0.5 before atmospheric extinction) hugging the horizon in eastern Sagittarius, a span of an outstretched hand at arm’s length to Venus’ lower left.
Inside the magazine
For a comprehensive guide to observing all that is happening in this month’s sky, tailored to Western Europe, North America and Australasia, obtain a copy of the December 2016 edition of Astronomy Now.
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