Looking Forward to the Planets in February and March 2021

Mercury passes between the Earth and the Sun on the 8th of February and thereafter moves into the morning sky. This is a very good apparition for equatorial and southern-hemisphere observers but is low as seen from the UK. Mercury, Venus, Saturn, Jupiter and eventually Neptune all cluster close together in this period with a number of conjunctions occurring but unfortunately these may be hard to observe. Mercury passes 4 degrees above Venus on the 13th and 14th of February but with Venus rising around 0715 UT in UK morning twilight, Mercury may be hard to catch. Mercury similarly sits slightly less than 4 degrees above Jupiter on the 14th and 15th but with Jupiter rising at 0700 UT the same visibility problem arises.

Orbital dynamics commit Mercury and Jupiter to a morning dance with the pair drawing much closer on the 5th of March, just 0.3 degrees apart, rising in the south-east around 0600 UT but only achieving 6 degrees of elevation at sunrise for mid-UK latitudes. Mercury’s geatest western elongation is on the 6th of March. On the 30th Mercury sits just below Neptune but the pairing is invisible from the UK.

Venus passes behind the Sun at superior conjunction on the 26th of March, but is lost to UK morning observation much earlier than that due to the very low angle of the ecliptic. If you want to see it then look to the south-east in the predawn sky in early February and you should find it a little before sunrise. Shining at magnitude -3.9 it can be followed into daylight but there are obvious risks to this with Venus still so close to the Sun. Venus passes just below Saturn on the 6th and Jupiter on the 11th but these conjunctions are only well-seen from the equator and the southern hemisphere.

In contrast Mars is best seen in the North. It is becoming small as Earth stretches away from it however south-transit in early February occurs at 1800 UT, after sunset, and at 55 degrees of elevation for the UK. At just under 8 arcseconds in apparent size detailed observation will not be easy but Mars won’t set until after midnight so prolonged observation at high elevation is easy into mid-evening. In the first week of March, Mars passes 3 degrees below the Pleiades making a good observational and photographic opportunity. As the period progresses Mars moves a little more westward with each sunset but remains at high altitude well into the evening and even in late March the red planet becomes visible around 45 degrees up in the south-west after sunset for mid-UK latitudes. By this time its size has fallen to 5 arcseconds and after this serious observation will end.

Jupiter is, as mentioned, a difficult and low morning object, initially rising only very shortly ahead of the Sun. It is certainly best seen from mid to late March onwards, rising around 0510 UT but still reaching less than 10 degrees of elevation by sunrise. Its magnitude -2 disk is nearly 35 arcseconds across and can carefully be followed into daylight with a south-transit of around 0935UT. Saturn is only slightly better placed; rising 20 minutes ahead of Jupiter by late March. Its ring system is similar in size, across, to the disk of Jupiter, and is tilted towards Earth by some 18 degrees with the north of the planet presented towards us by that amount. Like Jupiter it can be followed into daylight but both planets will be much better placed as we move forward into Summer.

Of the ice-giants, only Uranus is reasonably placed for observation as Neptune is in solar conjunction on the 10th of March. Uranus may best be found in early February a little below and to the west of Mars as full-night falls. At 50 degrees of elevation from the UK its 3.6 arcsecond disc will show only subtle shading at the eyepiece but infrared photography may show more detail. By early March Uranus has moved lower to the south-west as darkness falls and may be found some 30 degrees up, midway between Menkar in Cetus and Sheratan in Aries. After this, proper observation will be hampered by ever lower elevation. Catch this blue-green jewel as early in the period as you can for best viewing.

Alan Clitherow.