19 April 2024

Venus and Mars get close in the evening sky

13 February 2015 Ade Ashford

The view is 30° wide, or about 1½ times the span of an outstretched hand at arm’s length. Click the graphic to see a looping animation of the closing gap between Venus and Mars 14th—21st February. AN graphic by Ade Ashford

This week sees the start of a celestial dénouement between Venus and Mars, leading to a close conjunction on 21st February. A two-day-old Moon joins the scene on the 20th for a spectacular grouping: the pair of planets and the 5-percent illuminated lunar crescent all visible within the same binocular field of view.

The direction to look is low to the west-southwest horizon and the best time each evening is 1—1¼ hours after sunset, which is about 6:30 pm GMT for the centre of the British Isles (you can obtain sunset times from our online Almanac). If you leave it much later then you may see both Mars and Venus in a dark sky, but they will be much closer to the horizon.

The closing gap between Venus and Mars is, of course, merely a line of sight effect — the Red Planet is furthest away. The difference in brightness between the two worlds is also considerable: at magnitude -3.9, Venus is 120 times brighter than magnitude +1.3 Mars!

On February 14th, Mars was 2.17 astronomical units (202 million miles; 325 million kilometres) from Earth, while Venus was 1.45 AU (135 million miles; 217 million kilometres) distant. By the 21st, when the two planets will appear just 28 arcminutes apart — less than the diameter of the Full Moon — the distance to Mars will have grown to 2.2 AU (205 million miles; 330 million kilometres), while Venus will be somewhat closer at 1.42 AU (132 million miles; 212 million kilometres).

Sadly, neither planet is particularly well placed for telescopic observation at this time. Mars is a tiny 4.3 arcseconds in diameter with a 97-percent gibbous phase, while Venus grows slightly to 11.8 arcseconds with an 88-percent phase. To make Mars and Venus appear the same size as the Full Moon to the naked eye, you’d need to magnify them 430x and 160x, respectively.

So, for this planetary conjunction at least, the best way to appreciate the spectacle is with your unaided eyes or a pair of binoculars. Clear skies!