Starwatch: The August night sky

Graphic: Finbarr Sheehy

August brings Britain’s best views of the summer night sky. Our charts show the Summer Triangle looming in the S, its corners marked (in order of brightness) by Vega in Lyra, Altair in Aquila and Deneb in Cygnus. Capella in Auriga twinkles low in the NNE, below and left of Perseus and the radiant point for the Perseids meteor shower.

This annual display of swift meteors builds from a low level at present to peak on the morning of the 13th before petering out over the following week. An observer under ideal skies might count 80 or more Perseids per hour at maximum, their streaks seen in all parts of the sky as they diverge away from the radiant. With the Moon near new and the radiant climbing through the NE overnight to lie just E of the zenith before dawn, the official outlook for Perseids-watching is very favourable this year.

Perseids derive from Comet 109P/Swift-Tuttle which last reached perihelion, its closest point to the Sun, in 1992. It is now the turn of Comet 67P/Churyumov-Gerasimenko to reach perihelion and, with Europe’s Rosetta probe flying alongside and the Philae lander on its nucleus, we should have an exciting grandstand view as the comet hits peak activity.

Saturn is the brightest object low in the SW at nightfall but sets only minutes after our star map times. Dimming slightly from mag 0.4 to 0.6 during August, it is slow-moving in E Libra where it lies 2° below-right of the first quarter Moon on the 22nd.

After dominating our evening sky for months, Venus and Jupiter are now lost from view in the Sun’s glare. While Jupiter remains out of sight, reaching conjunction on the Sun’s far side on the 26th, Venus sweeps around the Sun’s near side on the 15th to emerge as a brilliant mag -4.3 morning star later in the month. By the 31st, it rises in the E at about 04:45 BST and stands 9° below and right of the much fainter planet Mars, mag 1.8.

Mars may be glimpsed as early as the 12th when it rises in the NE at 04:00 and stands 13° to the left of the slender waning and brightly Earthlit Moon. Use binoculars to catch Mars against the Praesepe or Beehive star cluster in Cancer on the 20th and 21st. Mercury remains hidden in our predawn twilight.