Mercury at greatest elongation east

2013 Oct 9

Mercury will be bright and well placed for observation in the evening sky.

Mercury is always close to the Sun in the sky since its orbit lies closer to the Sun than the Earth’s. On this day, however, it will reach its furthest point to the east of the Sun, meaning that it will set more than over an hour behind the Sun, appearing prominent at mag -1.9 on the western horizon for a brief time shortly after sunset.

Mercury is never very far from the horizon after the Sun has set, and so a clear western horizon is needed to get a good view of it.

At the moment of greatest elongation, Mercury will lie in the constellation Libra, at a distance of 25°20′ from the Sun. Its declination will be -17°53’00” , and so it will be seen to best advantage in the southern hemisphere.