Starwatch: Mercury joins Jupiter and Venus in the pre-dawn sky

The elusive inner planet Mercury is making an appearance in the morning sky, just before sunrise this week. Two days ago it reached its greatest separation to the west of the sun, a configuration known as greatest western elongation, and hence it rises before the sun. To see it you will need a good eastern horizon. Start looking about an hour before sunrise. On 18 December the sun will rise at 08:02 GMT from London, 08:21 GMT from Manchester and 08:55 GMT from Inverness. The chart shows the view at 07:15 GMT on 18 December from London. That particular morning, Mercury will be joined in the sky by Jupiter. The largest of all the solar system’s planets, Jupiter has just emerged from conjunction, when its orbit carries it behind the sun from Earth’s perspective. Also in the morning sky this week, but much higher in altitude, will be the dazzling “morning star” of Venus. It will be a radiant beacon of white light, outshining everything in the sky except the sun and the moon. Venus will rise at around 4am and stay be visible until the sun peeps above the horizon.