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The first three weeks of May offers an excellent opportunity for observes at Northern Hemisphere and tropical latitudes to spot elusive Mercury. During this apparition the planet is visible just after sunset low down above the west-north-western horizon. Peak altitude occurs on May 7th when greatest eastern elongation is reached. On this day, Mercury will be 21 degrees from our star and visible as a magnitude +0.2 point of light 10 or so degrees above the horizon, 45 minutes after sunset.

Due to the angle of the ecliptic, an apparition of Mercury is often better seen from one particular hemisphere. For this apparition, the Northern Hemisphere wins and this also happens to be the their most favourable evening apparition of the year.

Mercury as imaged by the MESSENGER space probe (NASA)

For example, at peak altitude on the evening of May 7th from 52N (e.g. London, England) Mercury is positioned 11 degrees above the horizon, 45 minutes after sunset. Afterwards its altitude decreases until it's finally lost to the bright evening twilight sometime during the third week of the month. It should be noted that Mercury is at its brightest before elongation - it fades from magnitude -0.4 to +1.5 during the first half of May. Located a few degrees northeast of Mercury is much more brilliant Venus (mag. -4.3).

The chart below shows positions of Mercury and Venus from latitude 52N (e.g. London, England). The view will be similar from other northern temperate locations.

Mercury evening apparition as seen from latitudes of 52N, 45 minutes after sunset

On May 12th, Mercury (mag. +1.0) passes 8 degrees north of orange giant star Aldebaran (α Tau - mag. +0.9) the brightest star in Taurus. The fast moving planet then reaches a stationary point on May 19th. Retrograde motion follows pulling Mercury back towards the Sun with it arriving at inferior conjunction on May 30th.

From the Southern Hemisphere the planet is not well placed for observation but may be glimpsed extremely low down at the start of the month.