Royal Astronomical Society of New Zealand

The Evening Sky in September

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.

Three bright planets light up the evening sky along with some of the brightest stars. At the beginning of the month Mercury appears as a lone medium-bright white star low in the west at dusk. It sets two hours after the Sun. On the opposite side of the sky is Saturn, the same brightness as Mercury but cream-coloured.  Around 8 pm golden Jupiter rises in the east.  It is the brightest 'star' in the night sky.  It rises earlier each night so is in the evening sky at dusk by the end of September.  Mercury fades and falls lower in the twilight, disappearing by the 18th.  

Jupiter and Saturn are worth a look in any telescope. A small telescope shows Jupiter's disk and the four 'Galilean' moons lined up on each side of it. A larger telescope shows stripes across the planet made by warm and cold clouds on Jupiter. Occasionally the shadow of a moon crosses Jupiter, making a tiny black spot. Jupiter is at its closest for this year, 590 million km away.  Almost any telescope will separate the planet and the ring. Saturn is 1350 million km away mid-month. The Moon will be near Saturn on the 8th and near Jupiter on the 11th.

Of the bright stars, Arcturus is on the northwest skyline. Its orange light is often broken up into red and green twinkling.  On the north skyline is Vega, a white star, the second-brightest northern star after Arcturus.  Vega is balanced by Canopus, the brightest true star in the evening sky, skimming along the southern skyline. Both stars are shining through a lot of air which makes them twinkle colourfully.  From northern New Zealand the star Deneb can be seen near the north skyline in the Milky Way, well right (east) of Vega. Deneb is the brightest star in Cygnus the Swan, a large cross-shaped constellation.  

Orange Antares, northwest of the zenith, 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. 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.  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 broad faint column of light extending upward (around Mercury at the beginning of the month.) 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.

Mars is in the morning sky (so not on the chart), rising after 1 a.m. It looks like an orange-red star, brighter than Saturn but much fainter than Jupiter. At the beginning of the month it will be between the Pleiades/Matariki star cluster and Aldebaran, the brightest star in Taurus.  Aldebaran has a similar colour to Mars but is fainter. The Moon will be near Mars on the morning of the 17th.

*A light year (l.y.) is the distance that light travels in one year: nearly 10 million million 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.

Notes by Alan Gilmore,
University of Canterbury's Mt John Observatory, 
P.O. Box 56, 
Lake Tekapo 7945,
New Zealand.