The Evening Sky in October 2016
Download a PDF containing this chart, additional charts for specific areas of the sky and descriptions of interesting objects visible at this time of year.
The Evening Sky in October 2016
Venus is the brilliant evening star appearing in the west at sunset. Above it is Saturn with orange Antares to its left. Higher again is Mars, brighter than Saturn and distinctly orange-red in colour. Venus and Mars hold their elevations, night to night, but Saturn and the stars slip lower. In the last days of the month Venus is between Antares and Saturn. The crescent moon is well to the right of Venus on the 4th, Saturn on the 6th and Mars on the 8th.
The apparent proximity of planets is just a line-of-sight effect. We are moving to the far side of the sun from slow distant Saturn. It is 1590 million km away mid-month. We are also leaving Mars behind but it more nearly matches Earth's speed, hence it is slipping only slowly down the sky. It is 172 million km away on the 15th. Venus is catching us up on the inside lane, 193 million km away mid-month. Saturn is the only one worth a look in a telescope. Venus and Mars are small gibbous disks.
Antares marks the heart of the Scorpion. (Scorpions don't actually have hearts, but this is star lore not entomology.) The Scorpion's tail loops up the sky in the evening, making a back-to-front question mark with Antares being the dot. The curved tail is 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. Red giants are dying stars, wringing the last of the thermo-nuclear energy from their cores. Massive ones like Antares end in a spectacular supernova explosion. Antares is about 20 times heavier than the sun. Above and 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.
Canopus is low in the southeast at dusk often twinkling colourfully. It swings up into the eastern sky during the night. Canopus is 13 000 times the sun's brightness and 300 light years* away. On the north skyline is Vega, setting in the early evening. It is 50 times brighter than the sun, 25 light years away and the 5th brightest star in the sky.
In the southwest are 'The Pointers ', Beta and Alpha Centauri, making a vertical pair. They point down to Crux the Southern Cross. Alpha Centauri, the top Pointer, is the closest naked eye star at 4.3 light years away. Beta Centauri is a blue-giant star, very hot and very luminous, hundreds of light years away.
The Milky Way is brightest and broadest in Scorpius and Sagittarius. In a dark sky it can be traced down to the south. In the north it meets the skyline right of Vega. From northern New Zealand the star Deneb can be seen near the north skyline in the Milky Way. It is the brightest star in Cygnus the Swan. 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, with a black hole three or four million times the sun's mass, is hidden by dust clouds in space. Its direction is a little outside the Teapot's spout. The nearer 'interstellar' clouds appear as gaps and slots in the Milky Way. The dust and gas has
come from old stars that have thrown much of their material back into space as they faded or blew up.
New stars eventually condense from this stuff. A scan along the Milky Way with binoculars shows many clusters of new stars and some glowing clouds of left-over gas. There are many in Scorpius and Sagittarius and in the Carina region.
The Large and Small Clouds of Magellan, LMC and SMC, look like two misty patches of light in the southeast sky. They are easily seen by eye on a dark moonless night. They are galaxies like our Milky Way but much smaller. The Large Cloud is about 5% the mass of our Galaxy and the small one 3%. That is still many billions of stars in each. The LMC is around 160 000 light years away; the SMC around 200 000 l.y.
On moonless evenings in a dark rural sky the Zodiacal Light is visible in the west. It looks like late twilight: a faint broad column of light around Venus, fading out at the Milky Way. It is sunlight reflecting off meteoric dust in the plane of the solar system. The dust may have come from a big comet, many centuries ago.
At the end of the month golden Jupiter is on the dawn horizon at 5 a.m.
*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.