Here’s a quick look at what’s going on in the sky during the month of September 2018. Remember, by early September, you’ll be able to spot Orion the Hunter rising in the early dawn hours!
All events are Eastern Time and as seen from the Northern Hemisphere:
September 2—Last Quarter Moon at 10:37 p.m. In this phase, the Moon appears as a half Moon. One-half of the Moon is illuminated by direct sunlight while the illuminated part is decreasing, heading toward the New Moon (invisible) phase. It’s called the “Last Quarter” Moon because this is the last quarter of the 29+ day lunar cycle. Note how it occurs approximately 7 days from the full Moon.
September 5—Look to the east before dawn to see if you can catch the phenomenon known as “False Dawn” or “Zodiacal Light,” best visible these next few months. You might think you’re seeing dawn break or the glow of some distant city, but it’s actually sunlight reflecting off dust particles. Read more about this phenomenon here.
September 7 – The waning crescent Moon is at perigee, its closest point to Earth in its orbit.
September 9—New Moon, at 2:01 p.m. At this stage, the Moon is not illuminated by direct sunlight and is completely invisible to the naked eye.
September 11–13—Look to the west, one hour after sunset, to catch the planets Venus and Jupiter with the waxing crescent Moon. Venus will be very low on the horizon. On the 13th, Jupiter and the Moon form a “wink.”
September 16—First Quarter Moon, 7:15 p.m. In this phase, the Moon looks like a half-Moon—one-half of the Moon is illuminated by direct sunlight while the illuminated part is increasing, on its way to full. It’s called the “first Quarter” Moon because, in this phase, the Moon is in its first quarter of the 29+ day lunar cycle.
September 17–19—As darkness falls, look to the southern sky to see the waxing gibbous Moon near Saturn and Mars. On the 19th, Mars will be directly below the Moon. Grab your telescope to make out Saturn and its rings, which will be to the right of the Moon on these nights.
September 19 –The Moon is at apogee at 8:47 p.m., meaning it’s farthest away from Earth in its orbit. An easy way to remember: Apogee “A” = Away.
September 21–Venus reaches greatest brilliancy on September 21st, shining at magnitude –4.8 and casting an eerily brilliant light from low in the west. Since the end of February, it has been a very prominent object in the evening sky soon after sunset. By month’s end, the Red Planet sets well before the end of twilight. Its sunlit hemisphere currently is oriented mostly away from the Earth, so it appears as a crescent. Telescopic observers may want to keep Venus under surveillance and watch this crescent grow rapidly thinner and longer. Even with steadily held binoculars, you might discern it, especially toward the end of the month, but unfortunately, Venus may be a bit too low after sunset to show a steady image. By mid-October, Venus sets only a half-hour after the Sun and then will be gone. It will pass between the Earth and the Sun on October 27th, then a couple of weeks later it will reappear in the predawn sky as a “morning star.”
September 22—The Autumnal Equinox, 9:54 p.m. While there’s nothing to see in the sky, this is the official first day of fall!
September 24—Full Moon at 10:52 p.m. At this phase, the visible Moon is fully illuminated by direct sunlight. But is it the full Harvest Moon or the full Corn Moon? Because this full Moon is nearest the autumnal equinox (September 22 in 2018) so it is the Harvest Moon. When the September full Moon is not the Harvest Moon, we call it the Corn or Barley Moon.
With contributions from Astronomer Joe Rao.