See the Mars-Venus-Moon conjunction of 31 January

By Ade Ashford

At dusk on the UK evening of Tuesday 31 January you can see (weather permitting) the 3-day-old crescent Moon, magnitude +1.1 Mars and dazzling magnitude -4.6 Venus all within the same field of view of a typical 7x binocular. AN graphic by Ade Ashford.
Anyone enjoying dazzling Venus in the west-southwest at dusk could be forgiven for thinking that it’s shining at its brightest, but the planet still has some way to go before it reaches its greatest brilliancy of magnitude -4.8 on 17 February.

But Venus is not the only naked-eye planet in the evening sky as night falls. Look half a span of a fist at arm’s length to Venus’ upper left where you will find Mars, which at magnitude +1.1 is 190 times fainter than its dazzling sibling.

The angular separation of Mars and Venus reaches a minimum of just under 5.4 degrees on the UK evening of 2 February; after that, the pair slowly drift apart. (We have to wait until the pre-dawn of 5 October this year to see Mars and Venus close again, separated by just ⅓ degree!)

But before all that, both Venus and Mars have a close encounter with a young Moon in the constellation of Pisces at dusk on Tuesday 31 January. The trio form an equilateral triangle small enough to be encompassed by the field of view of a 7x binocular low in the west-southwest for a couple of hours from 7pm GMT.

If you have a small telescope, Venus displays a 40 percent illuminated disc almost 31 arcseconds in diameter, requiring a magnification of little more than 60× to enlarge it to the same size as the adjacent Moon appears to the unaided eye. Venus is 50 million miles (81 million kilometres) from Earth on 31 January.

Mars, on the other hand, has a minuscule disc just 5.1 arcseconds in size — one-sixth that of Venus — on the UK evening of 31 January owing to a much greater distance of 172 million miles (277 million kilometres) from our planet.

Inside the magazine

For a comprehensive guide to observing all that is happening in the coming month’s sky, tailored to Western Europe and North America, obtain a copy of the February 2017 edition of Astronomy Now.

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