On March 31st, the inner planet Mercury reaches greatest western elongation and on this date is positioned 28 degrees from the Sun in the morning sky. This is an excellent opportunity for observers located at southern hemisphere and tropical latitudes; the planet is visible for an extended period of up to 6 weeks from about the middle of March. Unfortunately for those located further north, the angle of the ecliptic is unfavourable and consequently the planet is not suitably placed for observation.

Observing Mercury

A clear and ideally unobstructed view of the eastern horizon is recommended when searching for Mercury. On March 16th, from latitude 35S (approx. equal to Sydney, Cape Town and Santiago) Mercury will appear 11 degrees above the eastern horizon 30 minutes before sunrise. Although placed in the morning twilight, at magnitude 1.4 the planet should be a relatively easy naked eye target.

For this apparition, a good time period to look for Mercury is between March 21st and April 15th, when the planet will be at least 17 degrees above the eastern horizon, 30 minutes before sunrise. Its magnitude will also increase from 0.7 to -0.1 and therefore spotting Mercury should be very easy now, weather permitting of course! The peak altitude occurs on March 31st, the date of greatest elongation west, when Mercury is just over 20 degrees high with a magnitude of 0.2.

Once past greatest elongation west, Mercury continues to brighten as it begins to draw towards the Sun. For this apparition, the planet does not reach maximum brightness (mag -1.0) until the very end of the visibility period, more than 4 weeks after greatest elongation west!

The diagram below shows the March and April morning apparition of Mercury from latitude of 35S. The view will be similar for observers at latitudes near 35S.

Mercury data table from March 15 to April 30, 2013