Although Venus has been shining brilliantly in the evening sky during April my ‘star’ of the month was the planet Mercury. From the 1st April to the 16th April I observed Mercury with unaided viewing on six separate evenings. I made a point of observing the western horizon just after sunset from about 8.30pm until 9.15pm each evening when not completely obscured by clouds. Mercury’s angular distance west of Venus was a good guide to locating its position. Mercury has a yellowish colour all of its own and had a bit of a twinkle as it descended into the haze on the horizon. It was a delight to see. It will be back in the evening sky in August so my advice would be to make a bit of an effort and spend the time looking out for it and you will be well rewarded.
The following chart represents the night sky at 11.00pm BST on the 8th of May and at 10.00pm BST on the 23rd May. To use the chart, face south at the appropriate time with the bottom of the chart towards the horizon and you will see the stars in the chart. If you are observing earlier in the evening just turn eastwards by 15 degrees for every hour before the stated time but objects will be lower in the sky.
The constellation Ursa Major- The Great Bear, with its well known asterism, The Plough, has featured the last two months and we start with it again because it is such a good guide in the evening sky. You will find the end of the handle of the Plough directly above your head near your zenith. The stars Alioth, Mizar and Alkaid in the Plough’s handle form a natural arc so follow the direction of this arc down to the brightest star in that region. This is the star Arcturus, the second brightest star visible in the northern hemisphere with a magnitude of around -0.05 and at the relatively close distance of 36 light years. Arcturus is a red giant in the latter stages of its life and will eventually end up as a white dwarf. It is the brightest star in the constellation Bootes- The Herdsman but it is difficult to distinguish such a figure whereas the Kite asterism is easy to see and is what most people recognise as Bootes.The second brightest star in Bootes, Izar, is also shown because it is a beautiful star seen through a telescope, so take a look at it if you get the chance. It is a binary star consisting of an orange giant and a much younger blue white main sequence star.
The constellation Coma Berenices- Berenice’s hair, is also shown on the chart but it consists of relatively faint stars with little to attract the unaided observer. It said to represent the flowing locks of Queen Berenice of ancient Egypt and she apparently cut them off as a tribute to the gods after the safe return of her husband from battle.
Something to look out for
There are two lunar close approaches to keep an eye out for this month. On Tuesday 25th May a 4 day old Moon and Venus will be close in the constellation Gemini. On the following day, 26th May, there will be a close approach of the Moon and Mars in the constellation Cancer. You should be able to see these throughout the appropriate evening.