See bright Mercury shine before dawn

The last week of October and first days of November, 2021, offer a splendid chance for northern hemisphere stargazers to spot the planet Mercury in the morning sky.

Mercury shines above a high-flying aircraft catching the sunlight on 24 October at Walmer, UK. Image credit: Paul Sutherland

The innermost planet of the Solar System will be on a steep part of the ecliptic – the approximate path of the planets across the sky – which will lift it higher above the horizon than at many appearances.

For those of you at mid-northern latitudes, Mercury will get 10° or more above the horizon at best before the dawn twilight becomes too bright.

During the last week of October, Mercury will shine at around zero magnitude, in the constellation of Virgo. Look roughly due east to see it. You will need a clear horizon, unobstructed by buildings, hills or cloud.

A series of 41 exposures were stacked to produce this image of Mercury rising over the sea at Walmer on 24 October. The star trail above Mercury is Porimma (gamma Virginis), and vapour trails and a ship trail on the horizon are also visible. Image credit: Paul Sutherland

Mercury reaches “Greatest Elongation West”, when it appears its greatest angular distance, of 18° from the Sun, on 25 October. After that, it will gradually sink back towards the Sun from morning to morning, but will become twice as bright by the end of the first week of November.

Related: Read more about Mercury

Look for a fine, waning crescent Moon near Mercury on the morning of 6 November.

With the longer nights for northern dwellers in the last months of the year, it may not be so difficult to get out of bed to see Mercury, because it is rising at a more sociable hour.

Around 6am should be a good time, though check on a planetarium app such as Stellarium, and the changing of the clocks in many countries will also have an impact.

A simple image of bright Mercury shining below Porrima (gamma Virginis). Image credit: Paul Sutherland

Mercury is the closest planet to the Sun, at an average distance of 58 million km, and it is a rocky world like Earth. Its surface is mountainous and heavily cratered, like the Moon, because the planet has only a hint of an atmosphere.

Many people go through life without ever seeing Mercury because its appearances are fleeting and never in a really dark sky. So make the most of this opportunity if you can!


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