This is Dudley Observatory’s Skywatch Line for Friday, December 25, through Sunday, December 27, 2015, written by Alan French.
We have a rare Christmas full Moon to enjoy. It has been 38 years since there was a Full Moon on Christmas, the last being in 1977. The wait for the next Christmas Full Moon will not be as long – only 19 years.
Reaching full very early Christmas day, the Moon will rise at 5:09 pm Friday. Look for it toward the east northeast as it peaks above the horizon. With the proper choice of foreground this rising Christmas full moon would make a fine photo.
A rising full Moon can be a lovely sight. With its light passing through a thicker layer of atmosphere and more of the shorter wavelengths toward the blue end of the spectrum scattered, it is often orange. Its shape can also be distorted, often giving it a flattened appearance. An illusion also makes it appear larger when near the horizon.
The Moon will be due south and highest at 12:36 am Saturday morning, but catch it when you can – it will be a pretty sight among the bright stars of winter all night.
A bright waning gibbous Moon will rise at 6:09 pm Saturday and 7:11 pm Sunday.
Mercury is an elusive target. Because it orbits close to the Sun it can never appear high in the dark sky, and only makes brief excursions into the early morning or evening twilight skies. Right now Mercury is in the evening sky and can be spotted as darkness falls.
Look for Mercury at 5:15pm toward the southwest. It will be just under five degrees above the horizon, so you’ll need a good clear view to the southwest. Haze or clouds over hang near the horizon and might make it impossible to spot by eye. If so, try finding it by scanning the horizon with binoculars.
If the weather is uncooperative or you are unable to find Mercury, keep trying on following nights. Mercury is slowing fading, but it is also slowly moving higher into the evening sky, reaching just less than seven degrees above the horizon on the first days of January.