Total Eclipse of the Moon – 31 January 2018

On 31 January, 2018 a total eclipse of the Moon will be visible from eastern Europe, eastern Africa, Asia,   Australia, the Pacific Ocean and North America. During this lunar eclipse, the full Moon will pass through the Earth’s shadow (or umbra) lasting around 5 hours and 10 minutes from beginning to end.

Eclipse visibility diagram

Eclipse 2018 diagram
Courtesy of Fred Espenak –

Although not the deepest of total lunar eclipses, the total phase of the eclipse of January 2018 will last a  fairly respectable 1 hours and 17 minutes. The Moon will pass through the Earth’s shadow (or umbra) just underneath its central line.

Moon Earth shadow diagram
Courtesy of Fred Espenak –

How will the eclipse look in 2018?

The Moon will slowly turn from its familiar pearly white color to a reddish colour then back to its original colour all over a period of around five hours. The shade of red can vary from eclipse to eclipse depending on a few factors including conditions in the Earth’s upper atmosphere and the position of the Moon along its orbit. If there have been any significant volcanic eruptions for example, this can cause the eclipsed Moon to appear a much darker red than of other eclipses. The added amount of volcanic ash and dust in the Earth’s atmosphere can block more of the Sun’s light from refracting around the Earth during the eclipse causing deep, dark red effects.

The total lunar eclipse on 28 September, 2015 (photographed above) was considered particularly dark and this was not just down to volcanic eruptions or air pollution. The 2015 eclipse was during a perigee Moon when the Moon is closest to the Earth (coining the phrase ‘Supermoon Eclipse’ at the time). This meant that the Moon was deeper in to the Earth’s umbral shadow.

The eclipse on 31 January will also co-inside with a perigee Moon (on 30th) once again making this a ‘supermoon eclipse’. It’s hard to predict with certainty how red the  eclipse on January 31, 2018 will be. It’s best to wait and see and enjoy any surprises that this eclipse may reveal. During totality, many more stars can be seen than what could be seen during the full Moon. It’s a good photographic opportunity for a wide field shot of the eclipsed moon complimented by a background of stars.

Lunar Eclipse 31 January 2018 Animation

Lunar Eclipse Animation - 31 Jan 2018
Animation by Tomruen – Wikipedia

What causes the ‘Blood Red Moon’

During lunar eclipses, the Moon turns an orange-red colour which is the reason why lunar eclipses are sometimes referred to as a Blood Moon. This effect is caused by something called Rayleigh scattering. This is the same effect that causes the sky to look blue during the day and red during sunrise or sunset. During a normal full Moon, the Moon is simply reflecting back light from the Sun when it is on the opposite side of the Earth from the Sun. During a lunar eclipse, the Earth lies directly between the Sun and the Moon meaning the light should be totally blocked. However, some of this light gets scattered and reflected around the Earth’s atmosphere reaching the Moon. As sunlight passes through our atmosphere, the green to violet portion of the light spectrum is filtered out leaving the primarily red light to reach the Moon and reflect back to us. This is what causes the reddish colour of the Moon during a lunar eclipse.

Why is the 31 Jan, 2018 eclipse considered rare?

Although a total lunar eclipse is not rare (lunar eclipses occur once or twice a year on average), this eclipse coincides with a supermoon as outlined earlier. This is still not that rare as supermoon eclipses can occur every few years or so.  What makes this eclipse rare is the fact that it coincides with three significant lunar events. A total lunar eclipse, a supermoon (Perigee) and a blue Moon (when two full Moon’s occur in the same calendar month).  Having all three of these possibilities happen at once is quite rare indeed.

The last blue Moon lunar eclipse was March 31, 1866! The next blue Moon total eclipse will be Dec. 31, 2028. Read More about these lunar rarities in our article

The next Total Lunar Eclipse?

2018 is a good year for total lunar eclipses as the January eclipse is one of two total lunar eclipses to occur in 2018. The next total lunar eclipse takes place on 27 July 2018. More information on our dedicated page.