Mars caught by the claw

Les Dalrymple is a guide at Sydney Observatory and a keen all hours observer. Below he discusses one of our nearest neighbours, the red planet Mars.

Many have been outside in the early hours of the morning observing the parade of five planets in the pre-dawn sky. Among those, one more surprise awaits.

During the first week in February, the planet Mars will pass quite close by a medium bright star with an interesting history that is betrayed by its name. That star, Zubenelgenubi (try saying that without a smile on your face), is the brightest star in modern day Libra. Its name translated from the ancient Arabic, means “southern claw of the scorpion” and reveals it to be once part of the adjacent zodiacal constellation of Scorpius. Libra is actually a more recent invention by the Romans using stars abducted from the ancient form of Scorpius and was said to represent the scales held by Astrea — the Greek god of justice.

Mars, Libra and Scorpius in the pre-dawn sky this morning. Image made with <a href=" http://www.stellarium.org/">Stellarium</a>.
Mars, Libra and Scorpius in the pre-dawn sky of 12 February 2016. Image made with Stellarium.

Zubenelgenubi is a fairly nearby star, about 77 light-years away, and lying directly on the ecliptic (the plane of our Solar System), is often occulted by the Sun, Moon and planets. If you view it with binoculars, you will see it is actually two stars very close together and of differing brightness. Mars however, is a mere eleven light minutes away but is close enough to Zubenelgenubi in the sky that only your little finger at arm’s length can barely squeeze between the two.

While Mars is currently first magnitude and 200 million km distant, it is slowly brightening as the Earth (in a shorter orbit) catches up to it on our journey around the Sun. It reaches opposition (the point in the sky opposite to the Sun) on the 22 May, 2016 when it will appear almost as bright as Jupiter, and at about 76 million km distant, will be at its best for telescopic viewing for the next couple of years. During opposition, it will be seen among the stars of western Scorpius.

Why not book a visit to Sydney Observatory in late May or early June to observe the red planet first-hand through our telescopes. As a bonus, Jupiter and Saturn are also in the sky at that time and near their best too!

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