Every keen stargazer feels a quickening of the pulse at seeing a clear sky at dusk. This feeling intensifies when one is in with a chance of getting a naked-eye glimpse of Mercury. It is rightly regarded as somewhat elusive, but the innermost planet’s not particularly difficult to track down if you’re prepared to do a little homework to find out when and where to look for it. Mercury attains an elongation of 18.1 degrees east of the Sun at 1:25am GMT on 27 February.
This year’s finest evening apparition of Mercury for observers in the British Isles lasts about a fortnight starting 20 February. First, you need to find a location that offers you 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 UK. For any given day you can find out the time when civil twilight ends for where you live from our interactive online Almanac.
Mercury is brightest (magnitude -1.0) at the start of this two-week-long observing window around 20 February, and best placed from 25 February through 2 March when it’s 10° high at the end of civil twilight as seen from the centre of the British Isles. And I make no apologies for repeating the usual warning to protect your eyesight: never look for Mercury with binoculars or telescopes until after sunset. Happy hunting!
Why this is a good time to look for Mercury
As winter segues into spring, many casual skywatchers at temperate northern latitudes such as the UK express surprise at how rapidly the waxing young crescent Moon ascends in the western sky on successive nights, in stark contrast to dusk in autumn when the Moon appears to hug the southwestern horizon. The illustration below explains why this is so.