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Catch fleeting Mercury in the morning

Started by Geoffw, November 03, 2021, 07:14:36 am

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If you've never seen Mercury, then the next few mornings offer a great opportunity - but you'll need to be quick!

Mercury photographed in the morning sky on 28 October from Walmer, Kent, by Paul Sutherland

The closest planet to the Sun can never be seen in a truly dark sky because it cannot venture far enough away from it in the sky.

We only see it with the naked eye on one of its fleeting appearances in the evening or morning twilight, soon after sunset or just before dawn.

Currently, Mercury is in the morning sky and gets high enough above the horizon to be observable before the sky becomes too bright. The ecliptic - the path along which the planets appear to travel - is tilted steeply to the horizon on autumn mornings, from northern latitudes, so Mercury gets between 5° and 10° above the horizon before being lost in the dawn glow.

You need to look roughly eastwards to see Mercury, in Virgo. You will also need a clear horizon free of low cloud, buildings and hills. A sea horizon is ideal.

Mercury reached Greatest Elongation West on 25 October, when it lay 18° from the Sun, and shone at around -0.6, which is brighter than most stars.

Since then it has been slipping slowly back towards the Sun but you will have several more days into the first week of November to catch the planet it weather conditions are favourable.

Between 6.30 and 7am BST is an optimal time to seek out Mercury before the clocks go back on 31 October. After that, look an hour or so earlier local time, of course.

A fine waning crescent Moon will lie near Mercury on the morning of 6 November.

Binoculars will help you locate Mercury due to the brightening twilight sky and its low altitude. Make sure you don't scan the sky with them after sunrise when it will be to late to see Mercury anyway.

Mercury will reach Superior Conjunction, on the far side of the Sun, on 29 November, after which it moves back into the evening sky.