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Astronomical Note

For Earth-based observers, Mercury is often caught in the solar glare due to its tight orbit around the Sun. Your best bet for seeing this speedy planet is at twilight in the days around greatest elongation - when the angle between it and the Sun reaches a local maximum as seen from the Earth. Elongations are either East of the Sun (rising after the Sun) or West of the Sun (rising before the Sun). These elongations alternate throughout the year: an Eastern elongation is followed about 6-weeks later by a Western elongation which is followed about 10-weeks later by an Eastern and so on. Western elongations follow Eastern ones closely because the planet is racing past us during this time. The longer interval from Western to Eastern elongation is due to Mercury racing around the Sun and coming out "behind" us. 

You’ll get about six elongations in a typical year. The number of days either side of an elongation that Mercury is visible depends a lot on how far down to the horizon you can see. Mercury is brilliant, at about magnitude zero, around these times and twilight extinguishes most surrounding stars: you should have no trouble picking it out. If you have a clear horizon during an elongation, don’t put off an observation: Mercury, the fleet-footed messenger of the gods, doesn’t hang around for long.