Night sky guide for September 2018

The Moon will be located on the same side of the Earth as the Sun and will not be visible in the night sky on September 9. 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.

The September equinox on September 23 marks the first day of autumn for anybody living in the northern hemisphere and the first day of spring for anybody living in the southern hemisphere. On the day of the equinox, everywhere on Earth has almost exactly 12 hours of day and night, as the Sun's annual journey through the constellations of the zodiac carries it across the celestial equator.

The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated on September 25. 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. This moon is also known as the Harvest Moon. The Harvest Moon is the full moon that occurs closest to the September equinox each year.

• September 3 – Moon at Last Quarter – 02:39 UTC. The Moon will be prominent in the dawn sky, rising at around midnight. Over coming days, the Moon will rise later each day, so that it is visible for less time before sunrise and it less far above the eastern horizon before dawn. By the time it reaches new moon, it will rise at around dawn and set at around dusk, making it visible only during the daytime.

• September 5 – Asteroid 27 Euterpe at opposition. Asteroid 27 Euterpe will be well placed for observation, lying in the constellation Aquarius, well above the horizon for much of the night. Regardless of your location on the Earth, 27 Euterpe will reach its highest point in the sky at around midnight local time.

• September 7 – Close approach of the Moon and M44 – 02:27 UTC. The Moon and M44 will make a close approach, passing within 1°04' of each other. The Moon will be 27 days old.

• September 7 – Neptune at opposition – 18:13 UTC. Neptune will be well placed for observation, in the constellation Aquarius. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time. This is the best time to view and photograph Neptune. Due to its extreme distance from Earth, it will only appear as a tiny blue dot in all but the most powerful telescopes.

• September 9 – Piscid meteor shower. The Piscid meteor shower will reach its maximum rate of activity on September 9 but some shooting stars associated with the shower are expected to be visible each night from September to October. The maximum rate of meteors expected to be visible is around 10 per hour (ZHR). However, this assumes a perfectly dark sky and that the radiant of the meteor shower is directly overhead. By determining the speed and direction at which the meteors impact the Earth, it is possible to work out the path of the stream through the Solar System and identify the body responsible for creating it. To date, however, the parent body responsible for creating the Piscid shower has not been identified. 

• September 9 – New Moon – 18:03 UTC. The Moon will be located on the same side of the Earth as the Sun and will not be visible in the night sky. 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 10 – 21P/Giacobini-Zinner at perihelion and its brightest. Comet 21P/Giacobini-Zinner is forecast to reach its brightest, at around mag 6.5. It will lie at a distance of 1.01 AU from the Sun, and at a distance of 0.38 AU from the Earth.

• September 14 –  Conjunction of the Moon and Jupiter – 02:21 UTC. The Moon and Jupiter will share the same right ascension, with the Moon passing 4°22' to the north of Jupiter. The Moon will be 5 days old. At around the same time, the two objects will also make a close approach, technically called an appulse.

• September 14 – Close approach of the Moon and Jupiter – 04:45 UTC. The Moon and Jupiter will make a close approach, passing within 4°10' of each other. The Moon will be 5 days old. The Moon will be at mag -11.1, and Jupiter at mag -1.9, both in the constellation Libra. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

• September 17 – Moon at First Quarter – 23:16 UTC. The Moon will be prominent in the evening sky, setting around midnight. At this time in its monthly cycle of phases, it appears almost exactly half illuminated.

• September 17 – Conjunction of the Moon and Saturn – 16:30 UTC. The Moon and Saturn will share the same right ascension, with the Moon passing 2°03' to the north of Saturn. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -11.9, and Saturn at mag 0.2, both in the constellation Sagittarius. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

• September 17 – Close approach of the Moon and Saturn – 16:45 UTC. The Moon and Saturn will make a close approach, passing within 2°03' of each other. The Moon will be 8 days old. The Moon will be at mag -11.9, and Saturn at mag 0.2, both in the constellation Sagittarius. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – called a conjunction.

• September 18 – Asteroid 30 Urania at opposition. Asteroid 30 Urania will be well placed for observation, lying in the constellation Pisces, well above the horizon for much of the night. Regardless of your location on the Earth, 30 Urania will reach its highest point in the sky at around midnight local time.

• September 20 – Close approach of the Moon and Mars – 05:21 UTC. The Moon and Mars will make a close approach, passing within 4°43' of each other. The Moon will be 11 days old. The Moon will be at mag -12.3, and Mars at mag -1.6, both in the constellation Capricornus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

• September 20 – Conjunction of the Moon and Mars – 06:41 UTC. The Moon and Mars will share the same right ascension, with the Moon passing 4°46' to the north of Mars. The Moon will be 11 days old. The Moon will be at mag -12.3, and Mars at mag -1.6, both in the constellation Capricornus.

• September 20 – Mercury at superior solar conjunction – 01:38 UTC. Mercury 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. This occurs once in every synodic cycle of the planet (116 days) and marks the end of Mercury's apparition in the morning sky and its transition to become an evening object over the next few weeks. At closest approach, Mercury will appear at a separation of only 1°29' from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare.

• September 23 – September Equinox – 01:40 UTC. The Sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world. The September equinox marks the first day of autumn for anybody living in the northern hemisphere and the first day of spring for anybody living in the southern hemisphere. On the day of the equinox, everywhere on Earth has almost exactly 12 hours of day and night, as the Sun's annual journey through the constellations of the zodiac carries it across the celestial equator. The word equinox is derived from the Latin words aequus (equal) and nox (night) Wherever you live on Earth, on the day of the equinox the Sun will rise from the point on the horizon which lies due east, and set beneath the point which lies due west.

• September 24 – NGC 55 well placed for observation. Across much of the world NGC 55, a barred irregular galaxy in Sculptor will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -39°11', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 30°N. At magnitude 7.9, NGC55 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• September 25 – Full Moon – 02:54 UTC. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. 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. This moon is also known as the Harvest Moon. The Harvest Moon is the full moon that occurs closest to the September equinox each year.

• September 25 – Venus at greatest brightness – 04:17 UTC. In the southern hemisphere, Venus will be well placed for observation in the evening sky, shining brightly at mag -4.6. Venus's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time. It is observable only for a few weeks each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. On these occasions, however, Venus is so bright and conspicuous that it becomes the third brightest object in the sky after the Sun and Moon. It is often called the morning or evening star.

• September 27 – Makemake at solar conjunction – 13:28 UTC. 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.

• September 27 – 47-Tuc well placed for observation. Across much of the world the second brightest globular cluster in the sky, 47 Tuc (NGC 104), in Tucana will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -72°04', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 2°S. At magnitude 4.0, 47-Tuc is tricky to make out with the naked eye except from a dark site but is visible through a pair of binoculars or a small telescope.

Video courtesy Hubble Space Telescope

Sources: In The Sky by Dominic Ford, NASA, The Watchers

Featured image credit: Hubble Space Telescope. Edit: TW