It is time to bid farewell to Venus. Following a fabulous apparition in the evening sky these last few months, the planet is now disappearing into the evening twilight as it prepares to make its dash between the Earth and sun. This week presents a final treat that will not be easy to see, but will reward the effort. During midweek, Venus will pass within one degree of fellow inner planet Mercury. This is a close conjunction. One degree is just twice the diameter of the full moon. The chart shows the view looking north-west at 21.30 BST on 21 May. Venus will be the brighter of the two planets and will be obvious to the naked eye. Mercury will be tucked under, and much more difficult to glimpse. A pair of binoculars should easily reveal the pair but remember do not use the binoculars until the sun has set. From the southern hemisphere, the pairing takes place at twilight on 22 May. This time, Mercury will be just above Venus.