BAS Observer December 2017

6 BAS OBSERVER The sky in December by Peter Allison A nother trip around the Sun is almost complete. It will take many more future trips to see everything the sky and astro-catalogues have to offer, so start planning your observing dates and targets for 2018 – and your next trip around the Sun. Dark-sky nights So which days are unsuitable for Christmas parties this month? From about Thursday, 7th December, the Moon starts setting late enough to give some reasonably dark observing hours before it rises late in the evening. After New Moon you will have to wait until it sets to have a properly dark sky, so 7th–1 9 th December looks best this month. BEST DARK-SKY OBSERVING DATES FOR DECEMBER Day Date Moonrise Dark sky from sundown until moonrise Thursday 7th Moon rises at 10.06 p.m. Friday 8th Moon rises at 10.55 p.m. Saturday 9 th Moon rises at 11.3 9 p.m. Sunday 10th Moon rises after midnight. Monday 1 1 th Moon rises at 12.1 9 a.m. Tuesday 1 2 th Moon rises at 12.56 a.m. Wednesday 13th Moon rises at 1.32 a.m. Thursday 1 4 th Moon rises at 2.06 a.m. Friday 15th Moon rises at 2.42 a.m. Saturday 1 6 th Moon rises at 5.28 a.m. Sunday 17th Moon rises at 6.15 a.m. Moon interference until evening moonset Monday 18th New Moon Alignment stars Two prominent and widely spaced stars that are good for telescope alignment are Aldebaran in the constellation Taurus (the Bull), located on the ecliptic, and bright Canopus in the constellation Carina. Aldebaran is a great alignment star as it is bright and distinctly orange and therefore difficult to confuse with other stars in the eyepiece. Similarly, Canopus is also very bright, the second brightest of all stars in the sky after Sirius, and also easy to distinguish in the eyepiece. Taurus Carina Alignment stars: • Canopus • Aldebaran