Sky Diary
Find out what’s up in the night sky:
upcoming astoronomical events, interesting observations, packed with everything a stargazer needs to know
January 2018

*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:January 2
Last Quarter:January 8
New Moon:January 17
First Quarter:January 24
Full Moon:January 31, TOTAL LUNAR ECLIPSE
Total Eclipse of the Moon

January 2018 is an exceptional month regarding the Moon. There are two Full Moons this month, the first one on January 2 and the second one on January 31. Both Full Moons will be so called "Super-moons" because they occur just hours after the Moon reaches the perigeum, i.e. the point in its orbit which is the closest one to the Earth. Moreover, the second Full Moon is connected with the TOTAL LUNAR ECLIPSE, which will be fully observable in Australia, eastern Asia and in Alaska.

Observation of the Moon: Libration

Our Moon has the so-called locked (or synchronous) rotation, i.e. it rotates once per orbiting the Earth. Consequently, in theory, it shows always the same "face" to us and we can never observe its half, which is "behind". However, due to many physical reasons (e.g., the elliptical orbit, an un-even mass distribution, etc), the Moon also oscillates like a pendulum around an axis, which constantly changes its position. This particular motion is called the LIBRATION. Due to this property we can "peek around the edges" and observe around 59 per cent of the Moon's surface. The effect of libration is observable also by naked eye. Take a good atlas of the Moon, find Mare Crisium located on the Moon's north-eastern part (remember, the Moon's East is to its RIGHT on the Northern hemisphere!), and observe it during the month. You will notice that its form changes. Sometimes it is perfectly circular, sometimes it is more elliptical and closer to the Moon's north-eastern edge. This is the consequence of the Moon's oscillation, when Mare Crisium moves either towards the middle of the Moon or in the opposite direction.


Article by (C) G. Okša