The Planets
PICK OF THE MONTH
MERCURY BEST TIME TO SEE: 19 March, 18:50 UT ALTITUDE: 6º (low) LOCATION: Pisces DIRECTION: West FEATURES: Phase, surface shading occasionally visible through larger scopes EQUIPMENT: 3-inches or larger
Mercury reaches superior conjunction on 6 March, so it can’t be seen at the start of the month. However, the planet makes a rapid and impressive recovery mid month, due mainly to the steep angle the ecliptic makes with the western horizon at sunset at this time of year. Mercury never veers that far from the ecliptic and so its position in the sky is at its best in the spring evening skies.
On 14 March it sets 40 minutes after the Sun, so look for it around 20 minutes after sunset. It will be shining at mag. –1.4. Mag. –4.2 Venus sits 13º above Mercury on this date. If you can manage to get a telescopic view of Mercury after the Sun has set, you’ll see it has a tiny, 5-arcsecond disc that is almost a full circle. Mercury’s phase on 14 March is 94% lit.
Over the following days Mercury will be travelling along a distant part of its orbit to Earth, but gradually getting closer to us. The situation continues to improve for the rest of the month, making this an excellent opportunity to spot this elusive planet. Although it can be tricky to identify Mercury in an evening twilight sky at first, once you’ve managed it for the first time, it becomes very much easier on subsequent evenings.
By 31 March, a telescope will show that its disc now appears 7 arcseconds across and just 43% lit. The planet remains bright, being mag. –0.1, and it sets two hours after the Sun. Greatest eastern elongation occurs on 1 April, when the innermost planet will appear to be separated from the Sun by 19º.