Mercury reaches greatest eastern elongation on 10 February when it will appear east of the Sun separated by 18.2˚. This places it in the evening sky where it joins its Solar System neighbour Venus.
Unlike Venus, which reaches greatest eastern elongation on 24 March, Mercury’s greatest separation from the Sun means that it cannot be seen against truly dark skies.
Consequently, you’ll need to have a flat, uncluttered west-southwest horizon and clear skies to have the best chance of spotting this elusive world in February.
Venus by contrast will appear much higher in the sky after sunset.
Mercury is very well placed at the start of the month when it will appear bright and well separated from the Sun. On the 1st it shines at mag. –0.9.
By the time it reaches greatest elongation on the 10th, although its magnitude will have dropped to –0.4, its separation from the Sun will mean that it will set around 110 minutes after sunset.
Separation remains good for much of February, but Mercury’s brightness will continue to drop and this will make it harder to see.
It’ll probably be lost soon after 20 February when it shines at mag. +2.4, but sets just over an hour after the Sun. Inferior conjunction occurs on 26 February.
Getting a steady telescopic view of Mercury is quite tricky unless you’re set up to view it in daylight. Its inevitably low altitude after sunset means it’s subject to the vagaries of poor atmospheric seeing.
At the start of February, the planet presents a tiny 5 arcsecond gibbous disc, 83%-lit. At elongation on 10 February, the phase will appear at 50% illumination and the disc will be slightly larger at 7 arcseconds.
On the 20th, the dimmer planet will present an 8%-illuminated crescent, 9 arcseconds across.
Venus is the dominant planet in UK skies, a beacon in the southwest after sunset.On 1 February, a scope will show its 73%-illuminated disc 15 arcseconds across and shining at mag. –4.0.
It will set nearly four hours after the Sun on the 1st and be visible against dark skies for a couple of hours. By the month’s end, it remains visible for four hours and 20 minutes after sunset, shining at mag. –4.1.
Its appearance against a dark sky will have increased to around 2.5 hours by the 29th, its altitude being about 20˚.
On the 29th, changes in the apparent size and shape of Venus will be evident througha scope. It has an 18 arcsecond disc, 62%-illuminated.
How to see the planets this month
Best time to see: 29 February, shortly after sunset
Best time to see: 29 February, 05:30 UT
Altitude: 5˚ (low)
Mars is a morning planet rising a couple of hours before the Sun. It’s located in the constellation of Sagittarius and never rises high above UK horizons. Its shining at mag. +1.3 and appears small through a scope. On the 29th, Mars presents a 5 arcsecond gibbous disc, 90%-lit.
Best time to see: 29 February, 05:45 UT
Altitude: 3.5˚ (low)
The precession of morning planets continues after Mars with Jupiter. Unfortunately, as it is also located in Sagittarius, it remains too low for serious UK viewing at present. Jupiter shines at mag. –1.8 on the 29th.
Best time to see: 29 February, 06:00 UT
Altitude: 3˚ (low)
Wait long enough in the morning sky, and you’ll find Saturn bringing up the rear behind Mars and Jupiter. On 29 February, when all three planets have achieved a reasonable separation from the Sun in the morning sky, they form a distinctive line low in the southeast. And it remains low too, as all three planets are currently situated along the lowest part of the ecliptic as seen from the UK. On the 29th, Saturn is mag. +1.0.
Best time to see: 1 February
Uranus is fairly well positioned at the month’s start, but is west of south at true darkness. By the month’s end this situation has worsened and as true darkness falls the mag. +5.8 planet will be about 20˚ lower in the sky in the southwest.
Best time to see: 1 February
Neptune is located in Aquarius near to mag. +4.2 Phi (φ) Aquarii. Its position is now compromised, with the mag. +7.9 planet appearing low over in the west-southwest as darkness falls at the month’s start. As the month ends twilight will have engulfed Neptune.
Pete Lawrence is an experienced astronomer and a co-host on The Sky at Night. This article originally appeared in the February 2020 issue of BBC Sky at Night Magazine.