The New Moon will be on September 20 when the Earth, Moon and Sun all lie in a roughly straight line, with the Moon in the middle, appearing in front of the Sun's glare.
The Equinox will be on September 22 the Sun will be above the horizon for exactly half the time, everywhere on Earth, the official start of Spring here in Australia.
Monthly highlights, reposted from Source: American Meteor Society, In The Sky by Dominic Ford, include:
- September 6 - Full Moon - 07:04 UTC. The Moon will reach full phase at 07:04 on September 6. At this time in its monthly cycle of phases, the Moon lies almost directly opposite the Sun in the sky, placing it high above the horizon for much of the night. The sequence of full moons through the year are often assigned names according to the seasons in which they fall. This month's will be the third to fall in northern hemisphere's summer of 2017 – the Fruit Moon. This full moon was known by early Native American tribes as the Full Corn Moon because the corn is harvested around this time of year.
- September 9 - Conjunction of the Moon and Eris - 10:37 UTC. The Moon and Eris will share the same right ascension, with the Moon passing 8°12' to the north of 136199 Eris. The Moon, 19 days old, will be at mag -12.6 in the constellation Pisces, and Eris at mag 18.8 in the neighboring constellation of Cetus.
- September 15 - Conjunction of the Moon and Ceres - 21:56 UTC. The Moon and Ceres will share the same right ascension, with the Moon passing 5°14' to the south of Ceres. The Moon will be 25 days old. The Moon will be at mag -11.0 in the constellation Cancer, and Ceres at mag 8.9 in the neighboring constellation of Gemini.
- September 18 - Conjunction of the Moon and Venus - 00:57 UTC. The Moon, 28 days old, and Venus will share the same right ascension, with the Moon passing 0°32' to the south of Venus.The Moon will be at mag -9.6, and Venus at mag -3.9, both in the constellation Leo. The pair will be a little too widely separated to fit comfortably within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.
- September 20 - New Moon - 05:31 UTC. At new moon, the Earth, Moon and Sun all lie in a roughly straight line, with the Moon in the middle, appearing in front of the Sun's glare. In this configuration, we see almost exactly the opposite half of the Moon to that which is illuminated by the Sun, making it doubly unobservable because the side we see is unilluminated. Over coming days, the Moon will rise and set an hour later each day, becoming visible in the late afternoon and dusk sky as a waxing crescent which sets soon after the Sun. By first quarter, in a week's time, it will be visible until around midnight. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.
- September 21 - Conjunction of the Moon and Makemake - 12:18 UTC. The Moon, one day old, and Makemake will share the same right ascension, with the Moon passing 26°00' to the south of Makemake. The Moon will be at mag -8.4 in the constellation Virgo, and Makemake at mag 17.0 in the neighboring constellation of Coma Berenices.
- September 22 - September Equinox - 19:53 UTC. On this day, the Sun will be above the horizon for exactly half the time everywhere on Earth. According to the astronomical definitions of the seasons, this day marks the beginning of autumn in the northern hemisphere and of spring in the southern hemisphere.
- September 23 - Conjunction of the Moon and Haumea - 22:44 UTC. The Moon and dwarf planet Haumea will share the same right ascension, with the Moon passing 24°13' to the south of Haumea. The Moon will be at mag -9.9 in the constellation Virgo, and Haumea at mag 17.4 in the neighboring constellation of Bootes.
- September 26 - Makemake at solar conjunction - 07:04 UTC. Dwarf planet Makemake will pass very close to the Sun in the sky as its orbit carries it around the far side of the solar system from the Earth. At closest approach, Makemake will appear at a separation of only 27° from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare. At around the same time, Makemake will also be at its most distant from the Earth - receding to a distance of 53.39 AU – since the two planets will lie on opposite sides of the solar system. If Makemake could be observed at this time, it would appear at its smallest and faintest on account of its large distance.
Credit for top image: https://watchers.news/2017/09/01/night-sky-guide-september-2017/