Mars gets close to Neptune on December 31

2016 December 23

Stewart Moore

Following opposition on 2016 May 22, Mars is now saying goodbye as it heads into the sunset. Now only a shadow of its opposition glory of magnitude -2.1 and diameter 18 arc seconds, it shines at magnitude +0.9 with a diameter just under 6 arc seconds. Nevertheless, as a first magnitude “star” it is still quite obvious in the south-western sky and on December 31 acts as a guide to outer planet Neptune.

On December 31 the Sun sets (from mid UK latitudes) at around 15:54 with the end of astronomical twilight some 2 hours later at 17:59. At this time Mars will lie at an altitude of 24 degrees in the south-west (azimuth 213 degrees). The crescent Moon – new on the 29th at 07:00 – will be just a couple of degrees above the horizon and brilliant Venus, at magnitude -4.3, will lie approximately between the Moon and Mars, but closer to Mars.

Neptune, at magnitude +7.9, sports a disc diameter of just over 2 arc seconds but should be an easy binocular object less than one Moon diameter north-east of Mars. And being so close to Mars (23 arc minutes away), will comfortably fit into the field of a medium power eyepiece.

If the sky is clear (we can always hope) this should be a fascinating event on which to end 2016.

A very Happy Christmas to all and very best wishes for 2017.