PICK OF THE MONTH
MERCURY
BEST TIME TO SEE:
31 December, 07:20 UT ALTITUDE: 5º (low) LOCATION: Ophiuchus DIRECTION: Southeast FEATURES: Phase, surface markings through larger instruments EQUIPMENT: Naked eye, 8-inch telescope to see the disc
Mercury can be glimpsed low in the southwest just after sunset at the start of the month. The planet is dimming at this time and falls from mag. +0.2 on the 1st to mag. +1.5 by the 6th, when it will appear just 1.25º from mag. +0.9 Saturn. Look for the pair low in the southwest 25 minutes after sunset. Note that they will be very low at this time, so a flat horizon in that direction will be required to see them.
Mercury reaches inferior conjunction on 12 December, after which it rapidly reappears in the morning sky. It appears to pass mag. –3.8 Venus by a little over 2º on 15 December but, both planets being very close to the Sun, the chances of seeing this conjunction are slim. This won’t be helped by Mercury being a rather dim mag. +3.7. By 17 December Mercury will have brightened to mag. +2.4, and can be seen 1º south of an extremely thin waning crescent Moon. Planet and Moon will be above the southeast horizon about one hour before sunrise.
Things rapidly improve over the following mornings, with the planet appearing to move ever further from the Sun. As it does so, its brightness continues to increase and this makes locating Mercury in the dawn twilight, low above the southeast horizon that bit easier to do.
On the morning of 31 December, Mercury rises almost two hours before the Sun and will appear at mag. –0.2. The planet reaches greatest western elongation on 1 January 2018, when Mercury will appear separated from the Sun by 22.7º. This is a great way to welcome the New Year in if you’re a fan of the Solar System’s inner planet.