There is an absolutely beautiful cluster of celestial objects this week to look out for. The crescent moon will find itself close to the planets Venus and Mars, and the stars Castor and Pollux.
The chart shows the view looking west from London on the evening of Tuesday, 23 May, at 22.00 BST. The constellation of Gemini, the twins, will be upright and preparing to sink below the horizon, disappearing from view along with the twilight. Venus and the moon will be in between the body of the twins, which are marked at the heads by the stars of Castor and Pollux. Mars will be sitting off to the left of the constellation, glowing with its characteristic ruddy light. In contrast, Venus and the moon will be shining bright white. Castor and Pollux will be yellowish and blueish respectively.
The moon will be a relatively thin crescent, with only 17% of its visible surface illuminated. So the earthshine may be visible as well (see last week’s Starwatch). From the southern hemisphere the grouping is also easily visible. Instead of twilight, the view will take place in a fully dark sky. The twins will be lying on their sides, low in the north-west.