The Evening Sky in October 2015
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 2015
Saturn is the only planet in the evening sky. It is midway down the western sky at dusk and sets in the southwest around 10 pm mid-month. The moon is just below Saturn on the 16th and well to its right on the 17th. Above it, and fainter, is orange Antares, the brightest star in Scorpius.
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 opposite skyline is Vega, setting in the late evening. Vega is 50 times brighter than the sun and 25 light years away. Vega is the 5th brightest star.
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 way; 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. One sees a faint broad column of light passing through Libra. 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.
Bright planets appear in the eastern dawn sky. Brilliant silver Venus rises two hours before the sun through October. That's around 5 a.m. at the beginning of the month. Golden Jupiter is on the dawn horizon at 6 a.m. below and right of Venus. Between the two bright planets, at the beginning of the month, are the white star Regulus and the reddish planet Mars. They are similar in brightness but much fainter than the bright planets. Jupiter moves up the dawn sky. By mid-month it is passing Mars. The pair are less than a full-moon's width apart on the morning of the 18th. Around the 26th Jupiter passes by Venus, making an eye-catching pairing
of bright planets in the dawn. Jupiter and Mars are on the far side of the sun. Jupiter is 920 million km away; Mars 345 million km. Venus is on our side of the sun, 92 million km away on the 15th.
*A light year (l.y.) is the distance that light travels in one year: nearly 10 million million km or 10^13 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.