Brian Jones: Summer skies
Each season presents us with a different collection of stars, with winter, spring, summer and autumn all heralded by particularly prominent groups. Autumn nights reveal the legendary winged horse Pegasus carrying Perseus and Andromeda back home to the island of Seriphos and the dark winter sky plays host to the mighty hunter Orion, who strides majestically across the southern sky attended by his two faithful hunting dogs. Springtime sees the celestial lion Leo chasing the heavenly twins Gemini into the sunset while the summer skies are dominated by the three constellations Lyra, Cygnus and Aquila.
Stars from two of these summer constellations feature in an old Japanese legend which tells of two lovers – the beautiful Orihime and the shepherd Hikoboshi. After their marriage, they began to neglect their work to be with each other. This angered the gods who punished the couple by sending them to opposite banks of the heavenly river. They are only allowed to meet on one night – July 7th – which is celebrated as a holiday by children in Japan.
If you want to see Orihime and Hikoboshi, look high overhead after the sun has set. The first star to appear will be the brilliant Vega, the brightest star in the small but distinct constellation of Lyra and which, according to legend, represents Orihime. Halfway between Vega and the south-eastern horizon will be another bright star. This is Altair, the leading star in the constellation of Aquila the Eagle, and which represents Hikoboshi. If the night is dark and clear you may see the heavenly river stretching between them, running from the northern horizon right across the sky and down towards the south. This heavenly river is in fact the Milky Way.
Our Sun is just one member of a gigantic spiral formation of stars called the Galaxy, and the faint misty band of light we see crossing the night sky is our view as we look down along the galactic plane. The Milky Way is formed from the combined glow of countless thousands of stars, each of which is a member of our Galaxy and all of which lie along the plane of the Galaxy. Although the vast majority of the individual stars within the Milky Way are invisible to the naked eye, their combined light produces the faintly luminous band we see spanning the heavens.
A number of constellations depict birds, and the celestial aviary includes, amongst others, a peacock, a toucan and the legendary phoenix. Not all of these are visible from northern latitudes, although Cygnus the Swan, the most conspicuous of the celestial birds, is. Deneb, the brightest star in Cygnus, can be seen to form a large triangle with Vega and Altair. Known as the Summer Triangle, this formation is very conspicuous and straddles the Milky Way.
Deneb is located to the east of Vega and, depicting the tail of Cygnus, this star marks the top of a large cruciform pattern. From Deneb the rest of Cygnus can be picked out easily, the swan’s outstretched wings and characteristic long neck prominent as it flies along the Milky Way. When seen on a clear, moonless night, the overall effect of this prominent pattern of stars seen against the backdrop of the Milky Way can be quite striking.
Cygnus is associated with many stories. On the Euphrates it was likened to the fabulous Roc of the stories of Sinbad the Sailor. The group also bears the unofficial title of the Northern Cross, and the American astronomer Percival Lowell wrote of it in 1844 that the countless splendours in the sky were ‘crowned by the blazing Cross hung high o’er all’ – praise indeed!
The third and southernmost of the three stars forming the Summer Triangle is Altair, the brightest star in the constellation Aquila the Eagle. Located over the south eastern horizon during summer evenings this constellation, it’s leading star Altair in particular, is fairly prominent. Now that the warm summer evenings are upon us, why not check out the Summer Triangle? We’ve looked at Cygnus and Lyra in previous blogs, although Aquila has yet to feature, so we’ll check this constellation out next month. Until then, happy stargazing!
