The Evening Sky in September 2017

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 September 2017

Jupiter is the 'evening star', appearing midway down the western sky soon after sunset. It sets before 9 pm mid-month. We are leaving Jupiter behind on the far side of the Sun. It is 940 million km away. A small telescope shows Jupiter's disk and the four 'Galilean' moons lined up on each side of it. The thin crescent Moon will be below Jupiter on the 22nd.

Saturn is the only other naked-eye planet in the evening sky. It is just north of overhead at dusk, the brightest 'star' in that area. It sets in the southwest around 1 a.m. Saturn is 1500 million km away mid-month. Saturn is worth a look in any telescope. Good binoculars will show it as an oval, the planet and rings blended together. The Moon will be near Saturn on the 27th.

Arcturus is on the northwest skyline. Canopus, the brightest true star in the sky, skims along the southern skyline. Both stars are shining through a lot of air which makes them twinkle colourfully. Canopus, being white, shows all colours like a diamond. Orange Arcturus twinkles red and green. Canopus is matched on the northern skyline by Vega, the second-brightest northern star after Arcturus.

Canopus is a truly bright star: 13 000 times the sun's brightness and 300 light years* away. Vega is 52 times brighter than the sun and 25 light years away. 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. Deneb is around 1400 light years away and 50 000 times brighter than the Sun.

Orange Antares, well left of Saturn, marks the body of the Scorpion. The Scorpion's tail hooks toward the zenith like a back-to-front question mark. It 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. It is a relatively cool 3000 C, hence its red-hot colour. 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.

Midway down the southwest sky are 'The Pointers ', Beta and Alpha Centauri. They point down to Crux the Southern Cross. Alpha Centauri is the third brightest star. It is also the closest of the naked eye stars, 4.3 light years away. Beta Centauri, along with most of the stars in Crux, is a blue-giant star hundreds of light years away.

The Milky Way spans the sky from north to south. It 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, 27 000 light years away, is in Sagittarius. The actual centre is hidden by dust clouds in space. At the very centre is a black hole four million times the sun's mass. Dust clouds near us 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 in the south sky. They are 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.

On moonless evenings in a dark sky the Zodiacal Light is visible in the west. It is a faint broad column of light surrounding Jupiter and extending upward toward 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.

Venus (not shown on the chart) is the brilliant 'morning star' rising after 5 a.m. all month. It appears a bit north of due east. It is up 80 minutes before the sun at the beginning of September but only 50 minutes before the sun at the end. So it will be increasingly difficult to see from places with high hills to the east. Mars and Mercury are hidden low in the dawn twilight,

*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 sunlight four years to reach the nearest star, Alpha Centauri.

Newsletter editor:

Alan Gilmore Phone: 03 680 6817
P.O. Box 57 Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
Lake Tekapo 7945
New Zealand