The Evening Sky in August 2016
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The Evening Sky in August 2016
All five naked-eye planets are visible in the early evening sky. Mercury, Venus and Jupiter are low in the west and shuffle around through the month. Mars and Saturn are north of overhead near Antares. Bright stars are widely scattered. Vega on the north skyline is balanced by Canopus low in the south. Orange Arcturus is in the northwest. The Southern Cross, Crux, and the Pointers are midway down the southwest sky. The Milky Way spans the sky from northeast to southwest.
Venus, the brilliant silver 'evening star' sets in the west an hour after the sun at the beginning of the month, extending to nearly two hours by the end. Jupiter, higher in the west and golden-coloured, sets steadily earlier through the month: at 9 pm at the start of August and before 8 pm at the end. Mercury makes its best evening sky appearance of the year. It is roughly midway between Jupiter and Venus at the beginning of the month. Around the 20th Mercury will be left of Jupiter but much fainter. It begins to sink back into the twilight at the end of the month. On August 27-28 Jupiter and Venus will be close together, easily included in the same view in a telescope.
At the beginning of August Mars, Saturn and Antares make an isosceles triangle north of the zenith. Mars is the brightest of the three and the same colour as Antares. Saturn is cream-coloured. Saturn stays put against the background stars. Mars moves steadily eastward. On the 25th Mars will be two degrees, four full-moon diameters, from Antares making a striking pairing of orange 'stars'. The planet groupings are line-of-sight effects, of course. On the 25th, when the planets are in groups, Mercury is 118 million km away, Venus 233 million, Mars is 128 million, Jupiter 951 million and Saturn 1475 million km.
Canopus, the second brightest star, is near the south skyline at dusk. It swings upward into the southeast sky through the morning hours. On the opposite horizon is Vega, one of the brightest northern stars. It is due north in mid-evening and sets around midnight.
Midway down the southwest sky are 'The Pointers ', Beta and Alpha Centauri. They point down and rightward to Crux the Southern Cross. Alpha Centauri is the third brightest star and the closest of the naked eye stars, 4.3 light years* away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away and thousands of times brighter than the sun.
Arcturus, in the northwest at dusk, is the fourth brightest star and the brightest in the northern hemisphere. It is 120 times the sun's brightness and 37 light years away. When low in the sky Arcturus twinkles red and green as the air splits up its orange light. It sets in the northwest around 10 pm.
Antares marks the heart of the Scorpion. The Scorpion's tail hooks around the zenith like a back-to-front question mark. Antares and the tail make the 'fish-hook of Maui' in Maori star lore. Antares is a red giant star: 600 light years away and 19 000 times brighter than the sun. Below or right of the Scorpion's tail is 'the teapot' made by the brightest stars of Sagittarius. It is upside down in our southern hemisphere view.
The Milky Way is brightest and broadest overhead in Scorpius and Sagittarius. In a dark sky it can be traced down past the Pointers and Crux into the southwest. To the northeast it passes Altair, meeting the skyline right of Vega. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. The thick hub of the galaxy, 30 000 light years away, is in Sagittarius. The actual centre is hidden by dust clouds in space. The nearer dust clouds appear as gaps and slots in the Milky Way. Binoculars show many clusters of stars and some glowing gas clouds in the Milky Way.
The Large and Small Clouds of Magellan LMC and SMC look like two misty patches of light low in the south, easily seen by eye on a dark moonless night. They are galaxies like our Milky Way but much smaller. The LMC is about 160 000 light years away; the SMC about 200 000 light years away.
*A light year (l.y.) is the distance that light travels in one year: nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes four years to reach the nearest star, Alpha Centauri.