Adrian Dening's Stars Over Somerset

Thursday, 2 January 2025 16:46

Monday 6th to Sunday 12th January 2025

On Monday 6th, a little after dark, there is an opportunity to see the clair-obscur visual effect known as the "Lunar X & V" on the Moon's surface. At 6pm, a waxing quarter Moon will be located towards the south, with Venus and Saturn disappearing below the horizon to the south west, while Jupiter and the constellation of Orion will be found towards the south east.

Sunlight falling at particular angles on the Moon creates different visual effects at different times during its orbit around us and in the case of the "Lunar X & V" (that resemble the shape of those two letters in the alphabet) the effect can be seen on the terminator, which is the barrier between sunlight and darkness on the Moon's surface. The "X & V" are only visible for a brief period at the time of a waxing quarter Moon and are caused by sunlight hitting the rim of certain craters.

You will need binoculars or a telescope to see the shapes, but beside the "V" is a dark, flat area called the Sea of Tranquility that can easily be spotted with the naked eye. It is where Apollo 11 landed in 1969.

Early astronomers with basic telescopes used to think that because these areas were dark and flat, they must be oceans of water. Of course we now know that not to be the case. The Sea of Tranquility does have a slightly bluish tint however, which is thought to be due to a higher metallic content in its rocks - nothing to do with water at all!

Sticking with the lunar theme this week, if you go back outside around 9pm on Thursday 9th, an 81%-lit waxing gibbous Moon will be located towards the south, just to the left of the Pleiades open cluster of stars.