Mercury, Venus and Saturn line up

If you have never seen Mercury before, now is a very good opportunity. The innermost planet that never strays very far from the Sun is currently well placed in the morning sky.

Mercury, Venus and Saturn photographed from Walmer, UK.
Mercury, Venus and Saturn photographed from Walmer, UK. Credit: Paul Sutherland

And as an additional treat for early risers, this fleeting and elusive world is very neatly lined up with two other pre-dawn planets, Venus and Saturn.

Venus is so brilliant at magnitude -4 that it is very obvious, shining over in the south eastern sky. So find that first and then use it to spot Saturn to its upper right (if you’re in the northern hemisphere) and Mercury to lower left.

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You’ll have to be quick to see Mercury as it doesn’t hang about, taking just 88 days to orbit the Sun. It reaches what is called its greatest western elongation on the 4th of December when it will rise about two hours before the Sun, shining at magnitude -0.5. That will be the optimum date to see the planet but you can catch it for a few days after that date too before it draws back towards the Sun again.

If you’re wondering what the bright star is just below Venus in the photo, which was taken on the morning of 2 December from Walmer, Kent, that’s the wonderfully named Zubenelgenubi, otherwise known as alpha Librae.

For more information on what is in the night sky right now, check out Skymania’s monthly chart here.

Positions of the planets on 4 December as seen from the latitude of London
Positions of the planets on 4 December as seen from the latitude of London

Mercury was in the news again this week after NASA’s Messenger space probe found evidence of water ice in the craters around its poles. Large amounts of hydrogen were detected around the planet’s north pole after being liberated by cosmic rays striking the surface.

It suggests there are deposits of ice in regions which never get any of the sunlight that would cause them to evaporate away, or more correctly to sublimate.

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By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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