The Full Moon on January 31

Published 2018 January 30

As the Moon orbits our planet, the angle from which the Sun illuminates the Moon changes constantly. From Earth, we thus see the Moon going through a cycle of phases of shadow. When the Moon is fully illuminated as seen from the Earth, the phase is known as a Full Moon.

The cycle of phases takes 29.53 days to complete (known as a synodic month). It is thus possible to have two Full Moons (or any other phase, for that matter) within a calendar month (except in February which has at most 29 days).

A second Full Moon in a month in informally known as a “blue moon”, while the second New Moon in a month is termed a “black moon” (Sky Guide, p 118).

During January 2018, it is Full Moon on the 2nd at 04:24 and on the 31st at 15:27. The Full Moon on the 31st is thus a Blue Moon.

During it’s orbit around the Earth, the distance between the Earth and the Moon is also constantly changing. The point in the orbit where the Moon is nearest the Earth is known as perigee. The moment of perigee is given in the celestial almanac section of the Sky Guide (pp 6-61).

The Moon reaches perigee on January 01 at 23:56 and on January 30 at 11:55.

When the time of a New or a Full Moon “closely” coincides with the time of perigee, that phase is sometimes called a “super moon” (Sky Guide, p 121), because the Moon’s angular size is then larger since it is closer (see the diagram below). The Full Moon on January 31 is thus a Super Moon.

Thus, the January 31st Full Moon is both a Blue Moon and a Super Moon.

Lunar phase and distances 2018

Around the time of a Full Moon it sometimes happens that the Earth’s shadow falls on the Moon. Such an even is known as a lunar eclipse. Informally, a lunar eclipse, particularly a total lunar eclipse, is known as a “blood moon”, since the Moon appears to turn reddish.

In a calendar year there will always be at least two lunar eclipses, and at most five. During 2018 there are two lunar eclipses, on January 31 and July 27. Both are total eclipses. The event on January 31 won’t be visible from southern Africa since it happens at about 15:30, but can be seen from most of North America, Oceania, Russia, Asia, Middle East, northern Scandinavia and eastern Europe.

So, the January 31st Full Moon is both a Blue Moon and a Super Moon and a Blood Moon, although from southern Africa, we will experience a Super Blue Moon only.

Two astronomy meetings you don’t want to miss

During March, two astronomy symposia, running back-to-back, will be hosted in Cape Town. Over five delightful days, the two symposia truly span the ages.

The first, hosted by the SAAO, is the “History Symposium 2018” (March 07 – 08), which will review the history of astronomy in South Africa.

The second, hosted by ASSA, is the Society’s 11th symposium, and is titled “Amateur Astronomy in the Digital Data Age” (March 09 – 11). The meeting will explore the various ways in which amateurs can collaborate with professionals, particularly by the use of data products from modern large scale astronomical surveys.

Register for both symposia to ensure your attendance, and join us for five days of astronomy goodness!

ScopeX 2018

Published 2018 January 12

The ScopeX organizing team has announced that ScopeX 2018 will be held on 15 September 2018. This year’s theme is “solar system weather”. Find out more at

ASSA announces the Overbeek Medal for observational excellence

Published 2017 July 24

Overbeek Medal

During a recent meeting of ASSA Council, the Overbeek Award was formalized.

The Overbeek Medal is to be given to any amateur ASSA member who has had his/her observational astronomy published in a recognized astronomical journal, including the Monthly Notes of the Astronomical Society of Southern Africa, MNASSA. (Read more)

Call for Observations: Meteors from comet C/2015 D4 (Borisov)

Published 2017 July 15
Southern African observers have a unique opportunity to confirm the existence of the potential meteor stream from comet C/2015 D4 (Borisov) on the early morning of 2017 July 29. The earth passes very close to the predicted centre of the 1-revolution stream at 02h22 SAST, at which time southern Africa is favourably placed to observe potential meteors from the comet’s debris stream. The next opportunity with earth so close to the centre of the stream only occurs in 2029, when southern Africa is also favoured, but the comet is then a further twelve years past perihelion. Observations are requested this year to confirm any meteors from the parent comet which passed perihelion in its 700 year orbit most recently in 2014. Read more.

ASSA Annual General Meeting 2017

Published 2017 June 26
The ASSA AGM will be held on 2017 August 02 at 20:00 at the SAAO Auditorium, Observatory, Cape Town. The meeting will be hosted by the ASSA Cape Centre.

Big 5 of the African Sky

Published 2017 June 23
The Big 5 of the African Sky – the five best deep-sky objects – are beautifully placed at this time of year for observing.

Find out more about the Big 5 and how to observe them and also how to qualify for this beautiful personalized mug!

SkyGuide 2017 competition winners

Published 2017 March 21, Updated 2017 May 08

Competition winner G. H. van der Poll (right) received his prize from ASSA President Dr. Pierre de Villiers at an event held in Fish Hoek last week. The prize, an iOptron Astroboy I, was sponsored by Andrie van der Linde of Eridanus Optics.

The second-place winner, Lynn Koch of Malmesbury, will soon receive a selection of astronomy books sponsored by Struik Nature.

11th ASSA Symposium

Published 2017 May 1

ASSA Symposium 2018 website

The 11th ASSA Symposium will be held in Cape Town from Thursday, March 08 to Sunday, March 11, 2018.

The theme – Amateur Astronomy in the Digital Data Age – has been chosen to promote the link between professional and amateur astronomers. The advance of astronomical technology with large surveys has opened new avenues where the amateur community can contribute to science: variable and double star work, comet discovery, supernova discovery, etc.

The four-day event starts with a “History of Astronomy in Southern Africa” session on Thursday, March 08. The “Astronomy in the Data Age” session starts on Friday, March 09. The symposium dinner is on Saturday, March 10.

Visit the ASSA Symposium 2018 website for further details. Past symposia are documented in the Historical Section’s symposia archive.

2017 astronomical highlights not to miss

(Download a large 2-Meg version of this image)