On Monday, 11 November 2019 just after 12:30pm GMT, suitably equipped observers in the British Isles can witness the start of a 3.7-hour spectacle that hasn’t been seen for three-and-a-half years — the silhouette of innermost planet Mercury crossing the face of the Sun. Here’s our online guide to observing this fascinating and comparatively rare event in complete safety.
On 18 June at the end of civil twilight in the UK, planets Mars and Mercury lie slightly less than one-quarter of a degree apart in the constellation of Gemini. Observing this conjunction will be a challenge from the UK as the pair will be just 5 degrees high in the west-northwest at civil dusk in bright twilight, which is about 50 minutes after sunset for London.
Mercury attains a very favourable western elongation of almost 28 degrees from the Sun on 11 April, which means that the innermost planet is a morning object in the eastern sky before sunrise. Antipodean skywatchers are in the enviable position of being able to see Mercury and Venus close together for several mornings in a dark sky before the onset of astronomical twilight.
The innermost planet’s best evening showing of the year for northern observers occurs during the fortnight starting 20 February. Skywatchers will get optimal views by sourcing a location that offers an unobstructed view of the horizon from west-southwest through west at the end of civil twilight, which is about 40 minutes after sunset for the heart of the British Isles.
A powerful European Ariane 5 rocket blasted off from French Guiana late Friday and boosted a pair of satellites into space for a seven-year plunge into the inner solar system, a voyage requiring seven planetary flybys to slow down enough in the sun’s gravitational clutches to slip into orbit around hellish Mercury.
Mercury attains its maximum westerly elongation from the Sun on 26 August, meaning that the innermost planet is currently well placed for observation from the UK and Western Europe in the eastern sky around 40 minutes before sunrise. In addition to those in the evening sky, you might just see all five bright naked-eye planets this month!
Have you ever seen the closest planet to the Sun? If you wish to tick Mercury off your To-See list, particularly if you live in the Southern Hemisphere, now until the middle of May is the time to be scrutinising the eastern sky about an hour before sunrise. Mercury also has a close encounter with an old crescent Moon on 14 May.