Celestial fireworks

Ken Kennedy of Dundee Astronomical Society tells us what to expect in the August sky. “The Summer Triangle is high in the August evening sky with Vega and Deneb almost overhead,” he says. “From a dark observing site, the cross of Cygnus can be seen aligned along the Milky Way with Deneb at the Swan’s tail and the beautiful double star, Albireo, at the tip of its beak.

“Through a small telescope Albireo is a stellar gem, one of the two stars being golden yellow and the other star a contrasting blue. Lying at a lower elevation in the south is the constellation of Aquila, the Eagle, whose brightest star is Altair.

“Although Aquila is an ancient constellation, it is not endowed with many bright stars and Altair stands out in an area of sky where its brightness is not challenged. Altair is bright because it is only 17 light years distant and is a white star about 1.8 times the mass of the sun. During August, Jupiter and Saturn will be below Altair, low in the south.

“November is associated with fireworks, but there is a treat of celestial fireworks this month. The Perseid meteor shower is most active over the three days of August 11 to 13, with a peak of activity on the 12th at 1pm.

“The best evening on which to look for these meteors will be the 11th into the 12th when more than 80 per hour may be seen. There tends to be a high number of bright meteors in this shower and with warmer conditions than during most meteor showers they are worth going out to have a look late in the evening and even better after midnight.

“The moon will be close to last quarter and will start to cause problems by about 2am. The meteors we see flashing across the sky are particles shed by Comet Swift-Tuttle, a comet discovered in 1862 which has an orbit of the sun of 133 years.

The comet’s orbit takes it relatively close to Earth and it has a particularly close approach in the year 3044.

“Comet C/2020 F3, known as Neowise, after the space telescope which discovered it in March, put on an unexpectedly good show in July. Having been closest to the sun on July 3, it emerged into the evening sky and brightened considerably. By mid July it was a bright naked-eye object low in the north at about midnight. Comet Neowise became fainter during later July and will only be seen during August with binoculars or a small telescope.

“Mercury may be seen low in the north-east before sunrise for the first week in August. Venus rises in the northeast at 2am and will be very bright in the east by 5am. Mars rises in the east at 10.30pm and will be due south as the sun rises.

“As the months pass, Mars will become brighter and by August its diameter will have grown to 18 arc seconds and will be a good target for medium-sized telescopes. It can easily be recognised by its distinct orange colour.

“Jupiter will be bright but low towards the south at 10pm and will be followed at a distance of 8 degrees by Saturn. Saturn is less bright than Jupiter but is at the same elevation so it can easily be found by looking a little eastwards of Jupiter.

“The moon will be full on the 3rd, at last quarter on the 11th, new on the 19th and at first quarter on August 25.”