On 31 January 2018, a rare lunar trilogy will happen. A Supermoon, Blue moon and a lunar eclipse will occur concurrently.Image: NASA.

Picture: NASA.

This lunar event is significant since it is occurring after 150 years. Such a celestial event last happened in 1866.

As per a previous report, the moon rotates in an elliptical orbit round the Earth. If it comes partly in the shadow of the Earth, it is referred to as the penumbral phase. Soon as it pertains completely in the shadow of the Earth it is referred to as the umbral phase.

When the moon comes from the shadow of the Earth it is called a lunar eclipse.

This is followed by the Supermoon. When the moon is closest to the ground, which is referred to because of its perigee stage, it’s known as the Supermoon.

Lastly, once the sun, moon, and the earth come in a direct line, it’s known as full moon. Now, when two full moons occur in a gap of 29.5 days, that is, in one month, it’s known as Blue Moon.

In 2018, a single full moon had occurred on 1 January and the next is slotted to be about 31 January. Hence, on 31 January, along with the lunar eclipse, Supermoon, a Blue moon may also happen.

Since the lunar event is expected to happen during the night, the moon will not go into total darkness, instead the light will be scattered and may appear red. Thus the name Blood Moon, for the way in which the moon will look on 31 January.