September’s sky brings the autumnal equinox, the harvest Moon paired with Saturn, and bright planets visible throughout the night. Also see Jupiter’s moons eclipse each other, the year’s earliest-rising last quarter Moon, and Neptune at its best.
The Sun
Days with an excess of 13 hours of sunlight come to an end on the 3rd. We won’t see 13 hours of daylight again until April 6.
The Equation of Time is 0 on the 2nd, and from now through December 25, the Sun will be ahead, or “fast.”
The last sunset in the 7:00pm hour is on the 12th. The next time the Sun sets later than 7:00pm will be March 23, 2027.
On the 16th, the Sun enters Virgo, the constellation that hosts our star for the longest duration during its annual path along the ecliptic, 44.5 days.
The autumnal equinox occurs at 8:05pm on the 22nd, when the center of the Sun crosses the celestial equator (0° declination) moving southward. Owing to atmospheric refraction and the Sun being a half-degree wide in our sky, the true “equal night” occurs three days later, on the 25th.
You may have learned that the Sun rises in the east and sets in the west, but only near the equinoxes is this entirely true. From now until December solstice, the Sun will continue to rise and set farther south of the cardinal points.
The Moon
The waning gibbous Moon approaches the Pleiades Cluster (M45) on the night of the 2nd-3rd, appearing as close as 1.2° west of the cluster just before twilight.
Last quarter Moon is at 3:51am on the 4th, and rising at 10:30pm the evening before, it is the earliest-rising last quarter Moon of 2026. Note also that the Moon is just west of the line connecting Capella and Aldebaran, lying just outside of the Winter Hexagon asterism.
The waning crescent Moon passes Mars this week, appearing 5.6° west-northwest of the red planet on the 6th, then 7.6° east of it the next morning.
On the 8th, the 9.1% waning crescent Moon will be 4.5° west-northwest of Jupiter. Turn your binoculars towards the Moon to observe not only the beautiful Earthshine, but also to see the Beehive Cluster, M44, 2.0° to the west.
An occultation of Jupiter by the Moon takes place at 2:57pm that afternoon, but at a solar elongation angle of just 30.5°, it is not recommended to try to see this one.
The following morning, on the 9th, the even more slender 3.6% crescent Moon lies directly between Regulus and Jupiter.
There is an opportunity to spot the very old Moon (just 18 hours before new) early in the morning of the 10th, when the 0.6% illuminated crescent rises at 5:38am.
The Moon is new at 11:57pm on the 10th, beginning Lunation 1283.
On the 13th, find the crescent Moon low in the west-southwest near Venus and Spica. It sets less than an hour after sunset. On the following night, it is better positioned higher in the sky, and 5.5° east-southeast of Venus.
Find Antares 5.1° west-northwest of the wide crescent Moon on the 17th.
The Moon is first quarter at 4:44pm on the 18th. Culminating at just 19.3° at 6:41pm, this is the most southerly first quarter Moon of the year. From sunset until 8:15pm, the first quarter Moon passes directly in front of the center of the Milky Way.
Join a worldwide celebration of the Moon on September 19 for International Observe the Moon Night, made special this year by the success of the Artemis II mission, the first crewed flight to the Moon in more than a half-century, and the first on in which humans saw a significant position of the lunar farside.
The dark limb of the 87% waxing gibbous Moon occults magnitude 4.2 iota Capricorni at 1:38am on the 23rd. Reappearance occurs 62 minutes later, when the star reappears from beyond Mare Undarum, the Sea of Waves, on the eastern limb.
Full Moon is at 12:46pm on the 26th. The full Moon closest to the autumnal equinox is traditionally called the Harvest Moon. For us in Rhode Island, the Moon rises at 6:23pm, just 12 minutes before sunset, meaning that the Moon will be fully above the horizon before the Sun sets. These are the best photographic full Moons because the foreground landscape is under golden hour illumination, so be sure to find an unobstructed eastern horizon
Another thing that makes the 2026 Harvest Moon special is its proximity to Saturn. After the Moon rises on the 26th, look for Saturn just below and to the left (southeast) of the Moon. The pair remain within 6 degrees of each other throughout the night.
The waning gibbous Moon, Uranus, and the Pleiades are all within a 6° circle (same field of view in binoculars) on the final evening of September.
The Planets
Mercury is in the evening sky, but is undergoing one of its least favorable apparitions of the year. The innermost planet sets less than a half hour before sunset until the 11th, and sets at a maximum of 45 minutes past sunset at the beginning of October.
During the last week of September, Mercury and Venus lie nearly parallel to the horizon, with Mercury to the right of Venus. The innermost planet attains a higher elevation than Venus on the 27th, when the pair are separated by 12.5°.
September is the last month to get a good look at Venus as the Evening Star. On the 1st, it lies 1.5° south-southwest of Spica (alpha Virginis), and continues to appear relatively close to the star for the next several days as the planet moves east-southeastward at 3/4° per day.
Venus will now be over ½ arcminute across, and observing it with a small telescope will clearly reveal its distinct crescent phase.
Watch the waning crescent Moon near Venus on the 13th and 14th.
Venus rapidly moves out of view in the southwestern sky during the latter half of September. It begins to set before the end of nautical twilight on the 18th, but do make the effort to see its thinning crescent and growing globe as the inner planet gets closer to Earth.
At a distance of 0.388 au, Venus reaches its maximum brightness on the 24th, at magnitude -4.8. Unfortunately, due to its position south of the ecliptic, combined with the low angle of the ecliptic on the horizon during this time of year, its brilliance is significantly diminished compared to when it is positioned higher in the sky during the later stages of twilight. We will see a much more favorable maximum brilliance of Venus on November 24, when the Morning Star shines at magnitude -4.8 near Spica.
Venus sets before Mercury on the 28th, and on the last evening of September, its 16% illuminated crescent sets just 35 minutes after sunset.
On the 1st of the month, Mars forms an isosceles triangle with Betelgeuse and Aldebaran, notable as all three objects have a reddish glow.
Mars lies along the line connecting Pollux and Betelgeuse on the 7th.
Mars rises at about 1:30am in Gemini, and has brightened to magnitude 1.2, closely matching nearby Pollux. As Mars draws closer to Pollux, compare the ruddy hue of the planet with the yellow-orange glow of the class K0 giant star.
The waning crescent Moon joins Mars on the 6th and 7th, and the Red Planet passes 0.9° north of Wasat (delta Geminorum) on the 9th and 10th.
Look for NGC 2420, a magnitude 8.3 open star cluster that lies over 10,000 light years away, 1.0° south of Mars on the 16th and 17th. On the 18th, Mars lies on the eastern segment of the Winter Hexagon asterism, and on the following morning it departs the familiar star pattern that it has been a temporary resident of since July 17.
Rising just after 1:00am, Mars crosses from Gemini into Cancer on the 24th. On the 25th, it will be in line with Castor and Pollux, as its brightness now slightly exceeds that of the nearer star.
Jupiter resides in Cancer at the beginning of September, rising at about 4:00am. Now that the giant planet is rising higher in the sky during astronomical darkness, we can once again observe its four large Galilean moons: Io, Europa, Ganymede and Callisto.
Last year we observed Saturn’s ring plane crossing, a phenomenon that occurs once every 15 years when Saturn passes through its equinoxes, and its equatorial plane is aligned with the Sun. This event allows us to view not only the rings edge-on, but also see the ringed planet’s moons pass in front of, and behind the planet. Jupiter also goes through seasons, although far less dramatic, with its axial tilt of 3.1° compared to Saturn’s 26.7°, and without a visible ring system to give us a clear hint. It does, however, have its four large Galilean moons, all of which orbit within 0.5° of the planet’s equatorial plane, and during the several weeks preceding and following Jupiter’s equinoxes, they can be seen occulting and eclipsing each other.
These mutual satellite events can be observed beginning in September and will last through March 2027. Since Jupiter is visible in our sky for a relatively short amount of time each morning in September (less than 90 minutes at the beginning of the month, and three hours at the end of the month), there are only a few chances to view these events, but there will be more opportunities later in the year when Jupiter is visible in the night sky for longer amounts of time.
Europa eclipses Io at 3:43am on the 17th, followed by an occultation at 5:54am. Another eclipse of Io by Europa occurs at 5:57am on the 24th. This time, the occultation occurs during daylight.
Jupiter, the king of the planets, enters Leo, the king of the beasts, on the 23rd.
Europa again eclipses Io at 5:57am on the 24th. This time, the occultation occurs during daylight.
Saturn
Saturn rises before Venus sets on the 2nd, marking the first night since mid-January when there is always at least one bright planet above the horizon during nighttime hours. The next time we will have a duration of night that is absent of any bright planets will be on March 26.
Saturn moves into Cetus on the 5th, and remains a resident of the celestial whale through February 2027. As the ringed planet is now only a month from opposition, it now appears at its largest and brightest in our sky, but the shadow of the planet on the ring just off of the eastern limb becomes less prominent, reducing the three-dimensional appearance of the ringed planet.
As Saturn nears opposition in early October, notice how the shadow of the planet on its rings becomes significantly less pronounced. The planet is also at its brightest, not only because there is less shadow and that we’re closest to it, but also, the opposition effect of the sunline on the rings results in the maximum amount of sunlight to reflect back towards us.
The ringed planet is joined by the full Harvest Moon on the 26th-27th.
Uranus
Uranus begins September as an evening planet, rising in Taurus before 11:00pm. With binoculars or a small telescope, Uranus appears as a magnitude 5.7 blue-green starlike object about midway between Aldebaran and the Pleiades Cluster.
Uranus is stationary on the 8th, and undergoes its apparent retrograde (westward) path through February 8, 2027.
Look for 37 and 39 Tauri, a pair of stars of magnitude 4.4 and 5.9, respectively, separated by 10 arcminutes, and oriented such that the brighter star is nearer the Pleiades. Follow the line through the dimmer star away from the Pleiades just over 2° to find magnitude 5.7 Uranus, which will have a pale blue-green hue.
Neptune
Neptune is at opposition in Pisces on the 26th, bringing the planet to its closest point to Earth for the year, at 28.876 au. For a few weeks surrounding opposition, Neptune shines at its brightest, magnitude 7.7, and appears largest in the sky. Observers with large telescopes under steady skies should be able to resolve Neptune’s 2.4 arcsecond disk and spot its largest moon Triton at magnitude 13.4 and elongated up to 16 arcseconds from the planet during its 5.88-day orbit.
Neptune can be found by extending the eastern segment of the Great Square of Pegasus southward by the same length. To zero in on the eighth planet, look 7.2° due west of Saturn – this is about half the height of the Great Square. With binoculars or a small telescope, you’ll come across two pairs of 7th-8th magnitude stars in a semi-parallelogram. The two parallel pairs are 1/3° and 1/2°, are oriented east-southeast to west-northwest (8 o’clock to 2 o’clock), and are separated from each other by about 0.9° in an east-northeast to west-southwest (10 o’clock to 4 o’clock) orientation. Look at the westernmost star of the western pair, HD 940. Neptune is 1.4° due south of this star in early September, and moves west-northwestward at about one arcminute per day..
Minor Planets
Pluto is in Capricornus, 9.0° south of Dabih (beta Capricorni).
Although we’re now a few weeks past its opposition, September is an ideal time for observing Pluto during the evening hours, as the 35 au distant dwarf planet is already well above the horizon after twilight fades. Pluto is at a dim 14.5 magnitude, putting it within reach of a 12-inch telescope under ideal conditions.
Observers and imagers alike may spot the magnitude 11.3 galaxy NGC 6907 just 1.1° south of Pluto. The barred spiral, located 103 million light years away, occupies just 3 arcminutes of sky.
Although its brightness will almost certainly wash it out, the 78.5% gibbous Moon can be used to locate Pluto just 0.9° to its south on the 21st.
Ceres, shining at magnitude 8.9 from a distance of 3 au in Gemini, passes 1.2° east of Tejat (mu Geminorum) on the 1st, and moving eastward at ⅓° per day.
On the 12th, it crosses the line about ¼ of the way from Mebsuta (epsilon Geminorum) to Alhena (gamma Geminorum).
Pallas, at magnitude 8.7 in Cetus, is several degrees south-southwest of Vesta, and moving south-southwestward.
Find theta Ceti (magnitude 3.6), and move 2.6° east-northeast towards magnitude 5.9 HD 5962. Pallas passes just 0.6° east of this star from the 9th-11th, while moving south-southwestward at about 18 arcminutes per day.
Towards the end of September, Pallas appears to approach magnitude 5.5 47 Ceti, ending the month just 0.5° north-northwest of the star.
2 Pallas, at magnitude 8.5, is just 3.0° east of theta Ceti on the 14th, and moves south-southwestward by 18 arcminutes per day.
Our brightest asteroid Vesta is now quite easy to observe, despite its location in a region of Cetus with few bright guide stars. The giant asteroid will be brighter than magnitude 7 until mid-November, making it an easy target for binoculars, even during bright moonlit nights.
Moving retrograde in Cetus, it is 2.8° southwest of Alrescha (alpha Piscium) on the 1st. As it continues to move south-southwestward several arcminutes per day, find magnitude 5.9 HD 11803, located 1.8° southwest of Alrescha. Continue southwest about 2.5° to find a zigzag of four 8th magnitude stars that stretches in a roughly north-south orientation, and is 1.2° in length. In early September, Vesta is 1.6° due east of the third star from the north. Vesta’s position with respect to the zigzag pattern should be easy to follow throughout the month as it moves southwestward at an increasing rate.
Later in the month, start at Alrescha (alpha) and xi Piscium and move 8° south-southwest of Alrescha to magnitude 5.0 HD 10550. The three stars form a slender triangle that will be just larger than a typical binocular field of view. Vesta, at magnitude 6.8, will be the brightest object closest to the center of this triangle. Its southwesterly motion of about ⅓ of a full Moon width per day should be easy to distinguish against the fixed stars.
Asteroid 192 Nausikaa, a main-belt asteroid that is about 85 kilometers in diameter, comes to opposition on the 30th at a distance of 0.817, bringing it to easy telescopic visibility at magnitude 8.5. It can be found 0.5° northeast of 36 Piscium and is moving westward at ¼° per day.
Stars & Beyond
September evenings, in many ways, offer ideal conditions for skywatching: nights are trending cooler, but not yet too cold to discourage the fair-weather astronomers among us from venturing outside, darkness sets in earlier and we gain 90 minutes of astronomical darkness during the month, and, lastly, some of the best sights in the sky are readily visible early in the evening along the summer Milky Way.
High overhead lies the departing season’s most prominent star pattern, the Summer Triangle. Anchoring it is Vega, its brightest star. Moving southward towards Altair we arrive at one of the season’s most notable binocular objects. Colander 399, sometimes referred to as Brocchi’s Cluster, and more commonly known as the Coathanger. Not a true cluster, the Coathanger is a chance alignment of ten stars from magnitudes 5.1 to 7.2 that lie at a range of distance from 235 to 1700 light years. Categorized as an asterism, its conspicuous 1.5° long bar is aligned exactly east-west, and it is the eastern end of it that brings us to an actual open star cluster. Imagine extending the bar by an extra star by looking just ¼ ° to the east of 7 Vulpeculae, the easternmost star of the Coathanger asterism to find NGC 6802.
A treat for those who enjoy observing object pairs, or, more specifically, an object within an object, NGC 6802 in Vulpecula lacks a Messier or Caldwell designation, but is easy to locate
Featured as one of the objects in Phil Harrington’s Binocular Observing Olympics list at the 2026 Stellafane Convention, NGC 6802 is easily visible with 10×50 binoculars from Stellafane’s Bortle 3-4 skies, and the cluster begins to take on a speckled appearance as some of its component stars begin to resolve under very dark skies.
NGC 6802 contains over 100 stars in an apparent rectangular area about 4 arcminutes north to south by 1 arcminute east-west, with its brightest members shining at 12th magnitude. A 4-inch telescope may resolve a dozen members, and the diffuse glow will progressively resolve into more stars with increasing aperture. The moderate density of NGC 6802 combined with its compact size give a hint of its great distance of over 10,000 light years.
The next time you visit the Coathanger, take a deeper journey into the Milky Way to explore the lesser-known but worthwhile cluster NGC 6802.
Elsewhere in the sky we see the Big Dipper low in the northwest, beginning to assume its “upright” position, as if standing ready to collect the late summer harvest.
The photons from the next anticipated outburst of the Blaze Star, T Coronae Borealis, are presumably still on their way to our solar system, but its host constellation is getting lower in the west each evening. By the end of September, it is out of the sky by midnight.
In the east, the Great Square, autumn’s prominent star figure, stands on its southeastern corner star, Algenib (gamma Pegasi) as the “Great Diamond” combs into the sky, slowly replacing the summer star patterns. Along with Pegasus rises Andromeda, to the northeast, and its prized Great Galaxy.
Finally, predawn observers will find the entire Winter Hexagon above the horizon, bringing with it the ideal conditions for observing some of our favorite winter objects in non-winter temperatures.
