Sky Diary
Find out what’s up in the night sky:
upcoming astoronomical events, interesting observations, packed with everything a stargazer needs to know
December 2017

*Observations are described for the NORTHERN hemisphere and can be made by naked eye, small binoculars or by small telescope.

Phases of the Moon
Full Moon:December 3
Last Quarter:December 10
New Moon:December 18
First Quarter:December 26

The visibility of this planet on the early morning sky slowly ends, because it moves towards its superior conjuction with Sun - i.e. Venus will be behind the Sun (and so not visible) at the beginning of next year. Consequently, it rises only about 30 minutes before Sun in the first half of December, and cannot be seen in its the second half.


This planet rises around 3 o'clock a.m. local time and its visual magnitude is 1.6 (slightly brighter than the Polaris). Next year 2018, in July, there will the Great Perihelic Opposition of Mars, which repeats each 15-17 years (the last one was in year 2003). Mars will be very bright, its disk in a telescope will have a large diameter and many interesting features will be observable using a large magnification. We shall bring a series articles about the visual observations of Mars next year.

Moon and Aldebaran

Similarly to October 2017, there are now two close approaches of Moon to the star Aldebaran (the constellation Bull). The first close approach is on December 3/4 (the night from Dec.3 to Dec.4), the second one on December 31 early morning. This would be a nice conclusion of year 2017!

Observation of the Moon: Lunar Maria

Visually or in small binoculars, the lunar maria [ˈmaːriə'] (singular: mare [ˈmaːre']) are large, dark plains on the surface of Moon. They were called maria, Latin for "seas", by early astronomers who were thinking they really contain the water. Today we know that they are of volcanic origin and contain various types of basalt. There is also oceanus (ocean) on the Moon, as well as smaller, dark patches with the names lacus (lake), palus (marsh), and sinus (bay). The names of maria can be found on any good Moon atlas. But one mare will be important for our next discussion of Moon's libration. It is placed in the upper right corner of the Moon (i.e. near its north-eastern boundary - remember reversing East and West on the Moon!), and it is called Mare Crisium (the "Sea of Crises"). This mare is easily observable from about 3-4 days after New Moon to about 3-4 days after Full Moon. Please, try to observe it in December by naked eye and/or by small binoculars. Does it preserve its circular form or not? More about this easy and interesting observation in next article.

Article by (C) G. Okša