Mercury Analemma

March 28, 2005


Provided and copyright by: Tony Cook
Summary authors & editors: Tony Cook

This photo sequence shows the planet Mercury in the evening sky exactly 33 minutes after sunset on 12 dates from the 17th of March 2004 to the 5th of April 2004 -- taken from Leeds, United Kingdom. Gaps in the sequence were a result of cloudy evenings. Mercury was brightest on the 18th of March and reached its greatest elongation, 19 degrees from the Sun, on the 29th of March.

This year the best evening viewing of Mercury for the Northern Hemisphere started around the 27th of February, with Mercury at its brightest on the 4th of March and at its greatest elongation, 18 degrees from the Sun, on the 12th of March. After which, it has rapidly dimmed and dipped lower in altitude each night as it approaches inferior conjunction with the Sun on the 29th of March.

Oddly, for this "prime" evening showing, Mercury isn't well separated from the Sun. However, the steep angle of the ecliptic on these late winter dates ensured that Mercury would be just above the horizon after twilight ended. The next time we'll be able to see Mercury in the evening sky, in late June and early July, it'll reach a greater elongation of 26 degrees but will appear at a much lower altitude above the horizon, deep in the summer twilight zone when it sets. Thus, it won't be as easy to detect for mid latitude, Northern Hemisphere observers. This variation in observing is because Mercury has the second most eccentric orbit (after Pluto) of all the planets. Mercury's visible greatest separation from the Sun ranges from 18 to 28 degrees.

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