As 2016 draws to a close, a planetary gathering is taking place in the constellation of Aquarius at dusk. Venus is the dazzling magnitude -4.3 ‘star’ low in the south-southwest as twilight fades to dark, while first-magnitude Mars lies some 12 degrees (about half the span of an outstretched hand at arm’s length) to Venus’ upper left. As illustrated above, the young crescent Moon also joins the show for a few nights starting New Year’s Eve. But unseen to the naked eye yet readily viewed in small telescopes, outermost planet Neptune is currently drawing toward a much closer conjunction with the Red Planet in the small hours of New Year’s Day.
Both Mars and Neptune will be below the UK horizon when they appear to brush by just 1.2 arcminutes (0.02 degrees) apart around 7h UT on 1 January 2017, but the pair may be seen in close proximity on the early evenings of New Year’s Eve and New Year’s Day.
If you are fortunate to have clear skies over the next two nights and get a chance to contemplate this juxtaposition through a telescope, reflect on the fact that magnitude +7.9 outermost planet Neptune is 4.56 billion kilometres (2.83 billion miles) away from Earth, or 18½ times farther away than magnitude +0.9 Mars. The Red Planet is, therefore, more than six-hundred times brighter than its distant planetary sibling during their epic close encounter. In a high-power telescope, Mars shows a small 5.7-arcsecond-wide disc, while Neptune’s is just 2.2 arcseconds across.
The view from North America
By the time astronomical twilight fades to dark in New York, NY on New Year’s Eve (~6:16pm local time), Neptune and Mars lie just ¼ degree (14 arcminutes) apart. Some three hours later, when darkness falls in Los Angeles, CA (6:23pm local time) on the west coast, the separation of the two planets will have shrunk to 8.4 arcminutes. At this time (02:23UT on 1 January 2017) and for a few hours hence, Mars and Neptune will be visible in the same field of view of telescopes employing magnifications of 300x or more.
The view from Australasia
By 10:30pm local time on the first night of 2017, the summer sky of the New Zealand capital will be dark enough to view Mars and Neptune just 4.9 arcminutes — less than one-tenth of a degree — apart low in the west. Some 1¼ hours later in the Australian capital (9:45pm local time), the sky will be sufficiently dark to see that the separation of the two planets has grown to 7.1 arcminutes.
Wherever you find yourself in the world, we wish you clear skies and a very happy, healthy and prosperous 2017!
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 January 2017 edition of Astronomy Now.
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