Even late-summer clouds don’t must smash an observing session — Saturn (at opposition in 2017) is seen on the middle of this picture in a patch of clear sky. Credit score: Alan Dyer
Venus lingers after sundown. Saturn reaches opposition Sept. 8 and Neptune reaches opposition on the twentieth. Jupiter dominates Taurus and Mars improves because it passes into Gemini. Mercury makes its greatest morning look within the Northern Hemisphere and the final week of September might provide a naked-eye comet.
Venus is seen within the west for as much as an hour after sundown. At magnitude –3.9, it’s straightforward to identify. On the 4th, a waxing crescent Moon is lower than 5° west of Venus. The next night they change locations, now 7° aside with the Moon southeast of Venus. The pair remains to be 5° excessive half-hour after sundown.
By mid-September Venus stays fairly low after sundown and is 3° from 1st-magnitude Spica — can you notice the star south of Venus, whether or not together with your eye or binoculars? Venus strikes into Libra in the previous few days of September. It stands 7° excessive within the western sky half-hour after sundown and stays seen for almost one other hour.
By means of a telescope, Venus reveals a 91-percent-lit disk spanning 11″ on the first. The section reaches 85 % by the thirtieth, with a slight enhance in diameter to 12″.
Saturn is seen all evening, rising quickly after sundown. It reaches opposition on the eighth. The planet stands 1.5° south of 4th-magnitude Phi (ϕ) Aquarii. Saturn’s retrograde movement carries it westward to some extent 3° east of Lambda (λ) Aqr by the tip of the month. The planet reaches its peak magnitude for the 12 months, briefly shining at magnitude 0.5 round opposition. At the moment, Saturn lies 805 million miles from Earth.
An thrilling occasion happens the morning of Sept. 17, as Saturn is occulted by the Full Moon from central and western Canada and the U.S. Within the Mountain time zone, the occasion happens quickly after 5 a.m. MDT, with the Moon about 10° above the western horizon. The Moon is 20° excessive on the West Coast, the place the occasion happens round 4 a.m. PDT. It takes virtually 30 seconds for the disk of Saturn to be lined. The rings will seem very faint in opposition to the good Moon. The Worldwide Occultation Timing Affiliation’s web site lists timing from varied cities: www.lunar-occultations.com/iota/planets/planets.htm.
Saturn is beautiful by means of a telescope. Its disk spans 19″. Our viewing angle will increase from 3.5° to 4.5° as Earth’s orbit carries us barely above Saturn’s ring aircraft. Early subsequent 12 months is the ring-plane crossing; earlier than then, Saturn’s rings attain a peak tilt of simply over 5° earlier than declining.
The most important axis of the rings now spans 43.5″. Look ahead to the 2 evenings on both aspect of opposition to see in the event you discover the rings are brighter than regular — precisely at opposition, the ring particles’ shadows are “hidden” from view as a result of alignment, leading to a brightness enhance. Often called the Seeliger impact (after German astronomer Hugo von Seeliger), the impact can also be enhanced by backscattering of daylight off the advantageous particles.
On Sept. 1, the japanese half of the U.S. sees Saturn rise with Titan only a few arcseconds off its southern limb. Titan shines at magnitude 8.4 and orbits in 16 days. It stands close to the planet once more on the Ninth, seventeenth, and twenty fifth.
On Sept. 2/3, Tenth-magnitude Tethys and Dione transit Saturn. The small, faint moons are arduous to identify in opposition to the intense disk, making this a difficult remark requiring bigger telescopes. Alternatively, high-speed video seize beneath excessive magnification can report the uncommon occasion. Within the Mountain time zone, the pair are in transit as Saturn rises. Tethys leaves the disk round 12:20 a.m. EDT (Sept. 3 within the Japanese time zone solely), with Dione following just below an hour later.
Iapetus reaches its biggest japanese elongation Sept. 3, when it seems close to twelfth magnitude. It stands 9.3′ due east of Saturn. The moon then strikes towards inferior conjunction early on the twenty third, brightening by a full magnitude. U.S. observers will see Iapetus simply 53″ north of Saturn on the night of the twenty second.
Neptune begins the month simply over 12° east of Saturn. It reaches opposition on the twentieth, when it stands 2.69 billion miles from Earth. Shining at magnitude 7.7, it’s a straightforward goal when viewing by means of binoculars. A telescope reveals a 2″-wide disk with a particular bluish hue.
Neptune is southeast of the Circlet in Pisces, only a quick distance from a parallelogram of 4 4th- and Fifth-magnitude stars. Neptune stands 3° north-northwest of the northwesternmost star (27 Piscium). The Full Moon passes inside 2° of Neptune on the 18th.
Uranus stands 5° southwest of the Pleiades (M45) all month after reaching a stationary level Sept. 1. It rises shortly earlier than 11 p.m. native daylight time on the first and two hours earlier by the thirtieth. The planet’s retrograde movement slowly picks up, carrying it some 20′ west through the month. There’s a pleasant pair of Sixth-magnitude stars, 13 and 14 Tauri, comparable in brightness to Uranus (magnitude 5.7) about 4.5° due south of the Pleaides. Uranus is inside 1.5° to the pair’s southwest. By means of a telescope, Uranus’ disk spans 4″.
Jupiter is an excellent object in Taurus, rising round midnight early within the month. The gasoline large dazzles at magnitude –2.3 and sits 10° northeast of Aldebaran, Taurus’ brightest star, on the first. A 20-day-old Moon joins in on the twenty third and twenty fourth.
The best views happen when Jupiter is highest above the horizon within the hour earlier than daybreak. Telescopes reveal darkish bands straddling the equator in addition to the 4 Galilean moons. The disk grows from 39″ on the first to 42″ by the tip of the month.
Europa transits Jupiter Sept. 1 between about 2:45 a.m. and 5:15 a.m. EDT. The beginning of the occasion is simply seen from the Mountain time zone eastward. On Sept. 8, Europa’s shadow transits between 2:40 a.m. and 4:08 a.m. EDT. Europa begins a transit about quarter-hour after the shadow transit ends.
Sept. 14/15 finds Io and its shadow transiting as Jupiter rises throughout the western half of the U.S. The shadow transit begins shortly after 1:10 a.m. EDT on the fifteenth; Io follows round 2:30 a.m. EDT. The shadow exits at 3:20 a.m. EDT and Io exits at 3:41 a.m. EDT.
Ganymede’s expansive shadow transits for the japanese half of the U.S. on Sept. 20/21. The occasion is underway as Jupiter rises and ends round 12:45 a.m. EDT on the twenty first. On Sept. 27/28, the moon’s big shadow crosses Jupiter’s south polar area from about 2:45 a.m. to 4:40 a.m. EDT on the twenty eighth. The curvature of the planet is obvious within the shadow’s elliptical form.
Callisto doesn’t transit, due partly to the inclined angle of the aircraft of its orbit to our line of sight. As a substitute, it skims close to the poles; an instance of this happens in a single day on Sept. 19/20.
Mars glows at magnitude 0.7 between the horns of Taurus as September opens. It crosses into Gemini on the Sixth, when it stands 16° north of Betelgeuse, Orion’s brightest star. Mars rises shortly earlier than 1 a.m. native daylight time on the first and about 40 minutes earlier by the thirtieth. It’s greatest noticed within the pre-dawn hours when it stands excessive within the sky.
The Crimson Planet sits 0.9° due south of M35 on the eighth. Three days later (the eleventh) it stands 1° due north of Eta (η) Geminorum, then takes three extra days to face 1° due north of Mu (μ) Gem on the 14th. The planet ends the month in the midst of Gemini; at magnitude 0.5 it outshines all of the Twins’ stars.
Mars is tiny, spanning simply 8″ by the thirtieth. Over the last three months of the 12 months, it can virtually double in obvious measurement because it heads for an early 2025 opposition. The best characteristic to see when Mars is that this tiny is darkish, delta-shaped Syrtis Main, seen within the pre-dawn hours the primary week of September.
September begins with a beautiful crescent Moon adjoining to Mercury within the morning twilight. They’re effectively above the japanese horizon an hour earlier than dawn. Mercury shines at magnitude 0.5 simply over 4° to the decrease proper (south) of the Moon.
Mercury reaches its biggest elongation west late on Sept. 4. It has brightened to magnitude –0.2 by daybreak on Sept. 5. Now’s Mercury’s greatest morning apparition for observers within the Northern Hemisphere.
By the Ninth, Mercury stands roughly a Moon’s width (30′) from Regulus and shines at a straightforward magnitude –0.7, in contrast with Regulus’ magnitude 1.4. It’s a stunning sight.
Mercury continues brightening, reaching magnitude –1 by the twelfth, when it’s 5° excessive within the japanese sky 45 minutes earlier than dawn. By the nineteenth it is best to nonetheless be capable to comply with the planet, now 3° excessive simply half-hour earlier than dawn however magnitude –1.3. Nonetheless, you’ll possible want binoculars to identify it in vivid twilight. Mercury shortly dips out of view, heading towards superior conjunction Sept. 30.
However even because the morning sky loses a planet, it good points a comet! C/2023 A3 (Tsuchinshan-ATLAS) climbs within the japanese sky earlier than daybreak and stands 14° south of a waning crescent Moon on the thirtieth. The comet is 5° excessive within the east about 45 minutes earlier than dawn. If the comet follows predictions — all the time a giant if — it might be close to magnitude 1, maybe sporting a tail.
A partial lunar eclipse happens Sept. 17/18, beginning at 8:41 p.m. EDT, shortly after moonrise within the Midwest. Most observers throughout the continental U.S. will see first umbral contact at 10:12 p.m. EDT. Previous to this, if the Moon is up, the duskiness of its northern limb might be obvious in twilight quickly after sundown. That is the penumbral shadow, which the Moon entered at first of the eclipse.
At its peak, the eclipse will cowl 8 % of the Moon for almost 63 minutes, with most eclipse at 10:45 p.m. EDT. It is going to be seen throughout the U.S. (aside from Alaska), South America, and most of western Europe and western Africa on the morning of the 18th. The eclipse ends at 12:47 a.m. EDT on the 18th.
The autumnal equinox happens at 8:44 a.m. EDT on Sept. 22 because the Solar, shifting alongside its annual path, dips under the celestial equator.
Rising Moon: Double craters and rilles
Take benefit of September’s gentle evenings to take a break from the deep sky and marvel on the element alongside the Moon’s terminator. When you get previous Tycho’s nice rays and the intense spot of Aristarchus, zoom in on the lunar southwest. Greater energy reduces the brilliance of the moonbeams.
On the fifteenth, the Solar has illuminated the southwestern shore of Oceanus Procellarum. The graceful-centered crater Billy has one of many darkest flooring on the Moon, managing to flee the mottling of a number of lava flows that we will see close by.
Sitting close to the terminator is the fascinating double crater Damoiseau M. The terrain’s complexity is revealed by the low Solar angle — tomorrow evening it received’t be fairly as spectacular. A little bit extra eye-catching simply to the south is one other double crater. On this pair, the japanese one clearly shaped later — it has sharper options and has blown away the opposite’s rim. Extra intriguing is the broad rille Rimae Sirsalis, an extended, straight valley created by the land pulling aside, probably as a result of Orientale affect nonetheless hiding on the western limb. It ought to nonetheless be seen on the sixteenth, however the shorter shadows are much less efficient in revealing the depth. For those who can, look carefully on the fifteenth after which come again after a few hours to see how the lighting has modified.
Meteor Watch: Comply with the ecliptic
There aren’t any main meteor showers throughout September. Nevertheless, a pre-dawn glow attributable to tens of millions of tiny mud particles filling our internal photo voltaic system will be noticed on clear moonless nights from very darkish places. This zodiacal gentle shines with comparable or a bit fainter brilliance than the Milky Manner and is positioned alongside the ecliptic, which is angled steeply to the horizon this month, enhancing your probabilities of seeing it.
The zodiacal gentle is a faint cone-shaped glow with a broad base in Leo that narrows greater within the sky by means of Most cancers and Gemini. With a New Moon on the 2nd, the primary two weeks of September are essentially the most favorable time this month to view this elusive phenomenon. Any glow from cities to your east will restrict the view.
Comet Search: See you subsequent time?
Catch your final seems to be of Comet 13P/Olbers as darkness units in. Plan to be away from metropolis lights, arrange throughout twilight, and have an honest northwest horizon. Sinking under 15° in altitude, fuzzballs like this lose distinction as their gentle attenuates by means of extra of Earth’s ambiance. You’ll desire a 4-inch scope to spy its delicate Ninth-magnitude glow.
Begin at magnitude 4.3 Alpha (α) Comae Berenices, shift north 1° to hit the intense globular star cluster M53, then east one other diploma to see the fainter NGC 5053. Initially of September, the comet is a bit farther east, however is probably going simpler to identify than NGC 5053 as a result of that globular is extra diffuse. Take time to notice their shapes and constructions.
Imagers will get an opportunity to see the coma’s carbon emission shut down. Because the comet crosses the orbit of Mars, our Solar simply isn’t robust sufficient to set off the basic inexperienced glow any longer.
In the meantime, we’re anticipating an excellent sight in October from the up-and-coming C/2023 A3 (Tsuchinshan–ATLAS).
Finding Asteroids: Within the clear
7 Iris stands out effectively from its environment this month, making it straightforward to determine. Not counting a handful of brighter stars, the Ninth-magnitude main-belt asteroid outshines the remainder of the sphere aside from the final week of the month, when it arcs by means of a richer discipline for a masquerade celebration.
As a substitute of leaping proper to our goal, start at Alpha1 (α1) and Alpha2 (α2) Capricorni, the excellent pair on the northwestern level of the Sea Goat. Are you able to break up them with the unaided eye? In any scope they’re two hanging gold stars. Then transfer northeast to seek out Iris.
John Russell Hind picked up Iris in 1847, naming it for the Greek rainbow goddess. Like him, evaluate the view by means of a small scope to a chart to see which dot doesn’t belong, then return one other evening to substantiate it has moved. The final two weeks of September are significantly good for dropping 5 dots onto a circle in a logbook and including Iris when you’ve discovered it. When the Moon passes by on the 14th, it might not intrude as a result of it’s far under the ecliptic, whereas Iris is above it. When the asteroid reaches perihelion in 2028, it can shine at a straightforward binocular magnitude of seven.
