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With New Year fast approaching sky watches have a final chance this year to catch a glimpse of the elusive planet Mercury low down in the morning sky. On the 23rd December the closest planet to the Sun reaches greatest western elongation and is visible as a morning object just before sunrise. At this time Mercury will be separated from the Sun by 22 degrees.

A good time to look for Mercury is on the morning of the 22nd or 23rd of December as not only will Mercury be visible but also a slim lunar crescent and 1st magnitude star Antares, resulting in a nice celestial conjunction.

Mercury, Moon and Antares - December 2011 Northern Hemisphere view

Mercury, Moon and Antares - December 2011 Northern Hemisphere view - pdf format

Look to the south-east part of the sky near the horizon about 1 hour before sunrise on the 22nd December. For this view, Northern Hemisphere astronomers have it slightly better than those in the South. From London (51.5N), Mercury will appear nearly 8 degrees high, shining at magnitude -0.3, with a 7% lit Moon about 11 degrees to the right (west). Six degrees, south of Mercury and only a little over 1 degree above the terminator is Antares. Being so low down and at magnitude +1.05 binoculars will make it much easier to spot the red supergiant and brightest star in Scorpio.

Twenty-four hours later the positions will have hardly changed with the exception of the Moon. The Moon is now an extremely slim crescent, only 2% illuminated lying below (south) Mercury and to the left or east of Antares.

Mercury, Moon and Antares - December 2011 Southern Hemisphere view

Mercury, Moon and Antares - December 2011 Southern Hemisphere view - pdf format

For a Southern Hemisphere observer, for example from Sydney (34S), the role is reversed. Antares will appear higher in the sky than Mercury, with the latter hovering only about 3.5 degrees above the horizon. As before, the crescent Moon will appear high in the sky on the morning of the 22nd before closing the gap between itself, Mercury and the Moon the next morning. Binoculars will again aid the viewer.

Mercury from the Messenger space probe (NASA/Johns Hopkins Applied Physics Laboratory/Carnegie Institution of Washington)

Mercury will continue to remain visible low towards the east until it disappears in the glare of the Sun towards the end of the month.

Caution

As always please use EXTREME CARE when using binoculars during daytime or twilight. Please make sure the Sun is below the horizon and don't look with binoculars at the region of sky where the Sun has just set. The golden rule is NEVER look at or near the SUN with any type of optical instrument, as it will cause irreversible EYE DAMAGE.