Starwatch: The summer triangle

We have known the giant “V” of bright stars high in our S sky on August nights as the Summer Triangle since Sir Patrick Moore popularized the name during his early Sky at Night TV programmes in the 1950s. Marked by the stars Vega, Deneb and Altair, and covered by our chart, it crosses the meridian before midnight at present, and still lingers high in the SW at nightfall in November.

The Milky Way flows through the Triangle, and diagonally across our chart from its lower-right corner, but can really only be appreciated in the absence of light pollution and (as tonight) bright moonlight.The Summer Triangle‘s brightest star, Vega, lies in Lyra the Lyre, and shines at mag 0.0 from a distance of 25 light years (ly). Infrared radiation shows it to be surrounded by dust and it may have planets too. Epsilon, 1.6° NE of Vega, is the Double Double – binoculars reveal two stars, each of which is in turn double if viewed telescopically.

We need a telescope, too, for M57 which lies between two stars farther S. Famous as the Ring Nebula, this so-called planetary nebula is the expanding gas shed by a star near the end of its life. Another planetary nebula, M27 or the Dumbbell, is an easier binocular object in the dim constellation of Vulpecula the Fox to the SE, and just above Sagitta the Arrow. Also in Vulpecula is the Coathanger or Brocchi’s Cluster whose binocular-brightness stars are arranged in the form of an inverted coathanger. Farther E, to the left of the Triangle, is the pretty form of Delphinus the Dolphin.

The V-shaped arrangement of the brighter stars in the much more populous cluster M11 led to its name of the Wild Duck Cluster. More than 6,000 ly away, binoculars show it near the SW corner of our chart in Scutum the Shield. Deneb, the leader of Cygnus the Swan, shines at mag 1.2, noticeably fainter than the mag 0.9 of Altair in Aquila the Eagle. Altair, though, lies only 17 ly away while current estimates put Deneb at some 1,550 ly and imply it is one of the powerhouses of our galaxy.

Cygnus is depicted flying to the SW, its wings outstretched from Sadr, and its neck reaching to a beak at Albireo. The latter is an attractive contrasting double star through a telescope. Chi, alongside the neck, pulsates between naked-eye and dim telescopic brightness (roughly mag 5 to 13) every 13 months or so. At present, though, it is approaching a minimum.

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