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The Evening Sky in October 2023
The brightest stars are low in the north and south. 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. Places in the north of Aotearoa NZ will see Deneb near the north skyline in the middle of the Milky Way. Deneb is the brightest star in the cross-shaped constellation of Cygnus the swan. It is one of the most distant stars visible to the naked eye, around 2600 l.y away. Its brightness is uncertain because of the distance uncertainty but it could be as bright as 200 000 times the Sun's luminosity. Saturn appears northeast of the zenith. It has a cream colour, unlike any star. It is at one end of a widely spaced line of stars going southward across the sky and down to Canopus. The star Fomalhaut, to the right of Saturn, marks the Southern Fish, Piscis Austrinus. Below and right of Fomalhaut is Achernar, the same brightness as Saturn. The line continues down the sky to Canopus.
Saturn appears as an oval in a low-powered telescope as the ring and planet merge. Larger telescopes show the ring and Saturn's biggest moon, Titan, four ring-diameters from the planet. Smaller moons are closer in. Saturn is 1360 million km away mid-month. The moon will be close to Saturn on the 24th.
Jupiter is a late 'evening star' at the beginning of the month, rising around 10:20. It is the brightest ‘star’ in the night sky, shining with a steady golden light. It rises four minutes earlier each night. By the end of the month it is up at dusk. At dawn it is in the northwest sky but then the second brightest ‘star’ after Venus (see below.) The Moon will be near Jupiter on the 1st and 2nd and again on the 28th and 29th.
Orange Antares is midway down the western sky. It marks the body of the Scorpion. The Scorpion's tail loops up the sky, making a back-to-front question mark with Antares being the dot. The curved tail is the 'fish-hook of Maui' in some Māori star lore. Antares is a red giant star: 600 light years* away and 19 000 times brighter 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.
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. 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, 27 000 light years away, is in Sagittarius. The actual centre, with a black hole 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 dust clouds appear as gaps and slots in the Milky Way. A scan along the Milky Way with binoculars shows many clusters of stars and some glowing clouds of left-over gas. There are many in Scorpius and Sagittarius and in the Carina region below Crux.
The Large and Small Clouds of Magellan, LMC and SMC, look like two misty patches of light in the southeast sky above Canopus. They are easily seen by eye on a dark moonless night. They are galaxies like our Milky Way but much smaller. The LMC is around 160 000 l.y. away; the SMC around 200 000 l.y. away.
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 reaching up toward Antares, 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, centuries ago.
Venus is the ‘morning star’, rising two hours before the Sun all month. It is brighter than Jupiter and silver- white in colour. The Moon will be below Venus on the 11th.
*A light year (l.y.) is the distance that light travels in one year: nearly 10 million million km or 10^13 km. Sunlight takeseight 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.
Notes by Alan Gilmore, University of Canterbury's Mt John Observatory, P.O. Box 56, Lake Tekapo 7945, New Zealand. www.canterbury.ac.nz