Autumn arrives at the end of the month, but summer isn’t quite over for stargazers. There are still a few warm evenings left for observing Mars and Saturn. Meanwhile, Jupiter and Venus are visible in the morning sky this September, but you’ll need to observe Venus at dawn as the month begins, before it vanishes in the glow of daybreak. And don’t forget the Moon, which appears near the planets and some bright stars.
The Sun, Moon and planets among the stars
A beautiful quartet graces the sky on the evenings of September 1 & 2: The first quarter moon joins Mars, Saturn and Antares, the brightest star in Scorpius. Try not to miss this grouping! Over the following two evenings, the Moon crosses in front of the Milky Way above Sagittarius, which is located close to the southern horizon.
Looking east on the morning of September 5, about 45 minutes before sunrise, Venus can be seen shining just above the star Regulus, in Leo the lion; Jupiter is located off to the right of the duo. A few nights later, on September 8, the full moon shines among the stars of Aquarius. Then late in the evening of the 13th and 14th, the waning gibbous moon will appear near two interesting objects: the Pleiades star cluster and the orange star Aldebaran, both in the constellation of Taurus. (As for the Sun, it will cross the imaginary border between Leo and Virgo on September 17.)
To follow the Moon you’ll have to get up early — or go to bed late — depending on your lifestyle. Around 4:30 on the morning of September 20, a thin waning crescent moon will pass below the giant planet Jupiter. Twenty-four hours later, the lunar crescent will join Regulus, in Leo.
On September 24, the new moon will be hidden in the Sun’s glare, but it returns to the evening sky on the 28th. Look to the west about 30 minutes after sunset and you’ll see a waxing lunar crescent shining between two planets — Saturn to the right and Mars to the left. The following evening, three objects form a vertical line above the western horizon: the Moon is on top, Mars is in the middle and Antares is at the bottom.
The constellations represent persons, animals and objects. Leo the lion (visible in spring), Taurus the bull (visible in winter) and Scorpius the scorpion (visible in summer) already existed about 6000 years ago. Around half of the celestial imagery known today comes mainly from the ancient Greeks. These images were later adopted by Ptolomy, who was born in 90 A.D. In 1930, the International Astronomical Union adapted 88 constellations to cover the sky of both hemispheres North and South.
This month, far from the city and ambient light, the Milky Way can be seen extending from the southwest to northeast horizon and passing overhead. With the naked eye, and good vision, about 3000 stars can be seen in the sky.
At the zenith, the three bright stars that form the Summer Triangle are still visible: There’s Deneb in Cygnus, Vega in Lyra and Altair in Aquila. Looking toward the south, Sagittarius appears just above the horizon. Its brightest stars, connected together, form the shape of a teapot: The steam escaping from the spout is the Milky Way!
Autumn allows us to rediscover two constellations visible in the east: the Great Square of Pegasus forms the front part of a winged horse’s body, and Andromeda the Princess represents the daughter of Cepheus and Cassiopeia, the king and queen of Ethiopia. Cassiopeia is easy to recognise in the northeast; its stars form the shape of the letter “W”.
The Great Bear appears low on the northern horizon. The handle of the Big Dipper curves toward the bright orange star, Arcturus, in the constellation of Boötes the Herdsman, above the western horizon.
Summer gives way to autumn on September 22: The fall equinox occurs on that day at 10:29 P.M. (EDT).