September brings a daytime occultation of Jupiter by the Moon, visible across Québec, while Venus shines brilliantly at dusk. This month also features Neptune at opposition, several close passes of the Moon near Saturn, Uranus and the Pleiades, as well as the autumnal equinox.
Times are given for Montréal in Eastern Daylight Time (EDT).
Sky events not to be missed
- September 2–3: The Moon passes near the Uranus–Pleiades pair. Below them, the star Aldebaran rises in the eastern sky.
- September 8: Jupiter is occulted by a very thin crescent Moon, visible during the day across Québec at around 2:50 p.m. EDT. Take extreme care with optical instruments: never point them toward the Sun.
- September 10: New Moon late in the evening, with Uranus beginning its retrograde motion the same day.
- September 14: A thin crescent Moon and earthshine appear near Venus at dusk, while Mercury gradually returns, very low in the western sky.
- September 22: Venus reaches its greatest brilliance, followed by the autumnal equinox at 8:05 p.m. EDT.
- September 25–27: Saturn and Neptune take centre stage around the Full Moon, with Neptune reaching opposition on September 25.
- September 29–30: The Moon returns near the Pleiades and Uranus, which are visible in the east as this celestial pair rises.
Celestial events, day by day
September 1: The Moon (82%) is positioned to the right of Saturn during the second half of the night from August 31 to September 1. This is the first Moon–Saturn encounter of the month. Neptune is visible to the right of Saturn with binoculars.
September 2: The Moon passes near Uranus and the Pleiades open star cluster (M45). On the evening of September 2, the Moon is to the right of this pair, then to the left on the evening of September 3, beginning around 11 p.m. EDT in the eastern sky. Uranus, located to the left of the Pleiades, requires binoculars or a small telescope to be seen. The star Aldebaran rises slightly lower in the sky.
September 3: Saturn and Neptune, both visible throughout the month, make their closest approach to one another. The two planets are visible in the east around 9 p.m. as Saturn rises. Neptune remains to the right of Saturn and can only be seen with binoculars or a telescope.
September 4: Last Quarter Moon (50%) at 3:51 a.m. EDT.
September 4: Venus reaches aphelion (the point in its orbit farthest from the Sun) at 11:06 a.m. EDT.
September 6: The Moon (28%) pays Mars a visit as it rises, around 2 a.m. EDT. The Red Planet is just below the Moon. On September 7, the pair is still visible, but the Moon (18%) is positioned to the left of Mars.
September 6: The Moon (22%) reaches perigee, its closest point to Earth, at a distance of 368,228 km.
September 8: As Jupiter rises, just before sunrise at around 4 a.m. EDT, the Moon (9%) is positioned just above it. Slightly higher and to the right of Earth’s natural satellite is the Beehive Cluster (M44).
September 8: Daytime occultation of Jupiter by the Moon, visible across Québec. A very thin crescent Moon (7%) passes in front of Jupiter. The event begins around 2:50 p.m. EDT, when the planet disappears behind the Moon’s disk, and reappears around 3:50 p.m. Observe with binoculars or a telescope, taking care never to point your instruments toward the Sun.
September 10: Uranus begins its retrograde motion at 3:29 p.m. EDT. This apparent change in direction is caused by Earth’s movement around the Sun and precedes Uranus’s opposition.
September 10: New Moon (0%) at 11:26 p.m. EDT.
September 14: Just after sunset, low in the western sky, the Moon (15%) and its earthshine pass near Venus, which is about to set. Venus shines brightly to the right of the thin crescent Moon. Mercury also begins to reappear, very low on the western horizon and difficult to spot, even with a perfectly clear view to the west.
September 18: First Quarter Moon (50%) at 4:43 p.m. EDT.
September 18: The Moon (53%) reaches apogee, its farthest point from Earth, at a distance of 404,261 km at 11 p.m. EDT.
September 22: Venus reaches its greatest brilliance at 1:32 p.m. EDT. With a magnitude of about -4.8, it is especially bright in the evening sky, even as it sets earlier each day.
September 22: Autumnal equinox at 8:05 p.m. EDT. Summer officially gives way to autumn.
September 25: Just after the nearly Full Moon (99%) rises in the east, the Neptune–Saturn pair appears around 7:30 p.m. EDT. Neptune, to the left of the Moon, can be seen with binoculars, and Saturn rises a little later to the right of Neptune.
September 25: Neptune reaches opposition. This is the best time of the year to observe it. From Montréal, Neptune can be seen for much of the night in the constellation Pisces, from about 9 p.m. until 4:39 a.m. EDT. Binoculars or a telescope are required to see it.
September 26: The Moon (100%) continues its journey, moving between Saturn, to its left, and Neptune, to its right. This marks the Moon’s second encounter of the month with the pair, visible in the east around 7:30 p.m. EDT.
September 26: Full Moon (100%) at 12:48 p.m. EDT.
September 27: The Moon (98%) is about to leave the Saturn–Neptune pair, moving farther away from Saturn to its left. It nevertheless spends one last night with the two planets.
September 27: Mercury reaches aphelion, the point in its orbit farthest from the Sun, at 4:57 a.m. EDT.
September 29: The Moon (89%) passes the Pleiades open star cluster (M45) for the second time this month. Rising in the east around 9 p.m. EDT, the pair remains visible throughout the night. Uranus is also visible just below the Pleiades. On the following night, September 30, the Moon is to the left of M45.
