Bright stars dominate

Ken Kennedy, of the Dundee Astronomical Society, tells us what we can expect to see in the August sky.

“Cygnus, the Swan, can be considered the summer equivalent of winter’s great constellation, Orion, as it is easily recognisable as a bright cross representing a swan flying along the length of the Milky Way.

“Look up high towards the south on August evenings and two bright stars will dominate, – Vega, of the constellation Lyra and to its east Deneb, the brightest star of Cygnus and one of the Summer Triangle. It is easy to imagine the swan with Deneb at the tail and Albireo at its head with wings extended towards delta and epsilon Cygni.

“The stars at the head and tail of Cygnus are remarkable in their own way. The distance to Deneb is slightly uncertain but is around 2,000 light years and with a diameter of 200 times that of our sun the luminosity has been estimated as being around 60,000 times greater than our sun’s.

“The brightness of Deneb is slightly variable and it is believed to be a pulsating variable which may indicate that it is evolving into a red supergiant star which will explode as a supernova in a few tens of millions of years, long before the end of our own sun’s life.

“Last month I mentioned the multiple star epsilon Lyrae as a challenging set of stars to separate with a moderate sized telescope. Double or multiple stars are probably more common than single stars like our sun and Albireo, in Cygnus, is one not to be missed as the two easily separated stars shine in wonderfully contrasting colours, one being blue and the other golden yellow. I never tire of looking at this beautiful pair of stars.

“For readers who have been looking for noctilucent clouds (NLC) this summer, skies have been very poor with few clear nights. Reported sightings of NLC from observers throughout Europe have been fewer than for many years. The AIM satellite which records NLC from orbit is out of action and the reason for the low numbers of NLC displays is not clear at present.

“The menu for August includes the annual fireworks, the Perseid meteor shower. The Perseids, as they are generally known, is accepted by many as the best meteor shower of the year. The best nights to watch for Perseids will be the 11/12th and the 12/13th as maximum occurs at 7pm on the 12th.

“Mercury is elusive this month as it is hidden in evening twilight at the start of August then moves towards the sun later in the month. Venus rises about three hours before the sun and shines brilliantly in the east at around 3am before fading into the dawn light.

“Mars gradually moves westwards from the sun but is not far enough away by the end of the month to be seen. Jupiter is low in the west at 10pm for the first week in August but by the middle of the month will set about that time. Saturn is low in the south-west in late evening setting at around 12.30am by mid month.

“The moon is full on the 7th, at last quarter on the 15th, new on the 21st and at first quarter on August 29.”