Night sky, September 2020: What you can see this month [maps]

A clear night sky offers an ever-changing display of fascinating objects to see — stars, constellations, and bright planets, often the moon, and sometimes special events like meteor showers. Observing the night sky can be done with no special equipment, although a sky map can be very useful. Binoculars or a good beginner telescope will enhance some experiences and bring some otherwise invisible objects into view. You can also use astronomy apps and software to make your observing easier, and use our Satellite Tracker page powered by N2YO.com to find out when to see the International Space Station and other satellites. Below, find out what’s up in the night sky tonight (Planets Visible Now, Moon Phases, Observing Highlights This Month) plus other resources (Skywatching Terms, Night Sky Observing Tips and Further Reading).

Monthly skywatching information is provided to Space.com by Chris Vaughan of Starry Night Education, the leader in space science curriculum solutions. Follow Starry Night on Twitter @StarryNightEdu and Chris at @Astrogeoguy.

Editor’s note: If you have an amazing skywatching photo you’d like to share for a possible story or image gallery, you can send images and comments in to spacephotos@futurenet.com.

Night Sky Guides:

When, Where and How to See the Planets in the 2020 Night Sky
The Top Skywatching Events to Look for in 2020
Best night sky events of September 2020 (Stargazing Maps)
Space Launch Calendar 2020: Rocket launches, sky events, missions & more

Calendar of Observing Highlights

Tuesday, Sept. 1 from 9:55 to 11:13 p.m. EDT — Moon occults star Tau Aquarii

In the eastern evening sky on Tuesday, Sept. 1, observers using binoculars and backyard telescopes (red circle) in the eastern half of North America can see the almost-full moon occult the medium-bright (magnitude 4.05) star designated Tau Aquarii or 71 Aquarii. That star marks the western knee of Aquarius, the Water-Bearer. In the Great Lakes region, the left-hand edge of the moon will cover the star at approximately 9:55 p.m. EDT (or 01:55 GMT on Sep 2). The star will reappear from behind the opposite limb of the moon at about 11:13 p.m. EDT. Ingress and egress vary based on your latitude, so start watching a few minutes before the times quoted above — or use Starry Night or another planetarium app to look up the exact times for your town.

Wednesday, Sept. 2 at 5:22 GMT — Full Corn Moon

The September full moon, traditionally known as the “Corn Moon” and “Barley Moon”, always shines in or near the stars of Aquarius and Pisces. In most years, the September full moon is the Harvest Moon — but October’s full moon will happen closest to the equinox — so it will have that honor. Full moons are positioned opposite the sun in the sky, so they rise at sunset and set at sunrise. Since the full phase will officially occur in the wee hours of Wednesday in the Americas, the moon will already look full when it rises on Tuesday evening.

Wednesday, Sept. 2 evening — Asteroid Pallas changes direction

On Wednesday, Sept. 2, the main belt asteroid designated (2) Pallas will complete a retrograde loop that began in May — causing it to temporarily stop moving through the background stars. On this night, the magnitude 10 asteroid will be located halfway up the southwestern evening sky — about a palm’s width to the right (or 6.25 degrees to the celestial west of the medium-bright star Zeta Aquilae, which marks the western wingtip of Aquila, the Eagle. After tonight, it will return to a regular eastward motion through the stars.

Thursday, Sept. 3 — Northern winter begins on Mars

On Thursday, Sept. 3, the southern polar axis of Mars will reach its maximum tilt of 24 degrees towards the sun, triggering the solstice, and the beginning of winter in Mars’ Northern Hemisphere. Mars’ longer year means that its seasons are longer, too — slightly more than five months. Viewed in amateur telescopes from our vantage point on Earth, Mars’ southern polar cap will shine as a bright, white spot on the red planet (although your telescope’s optics may flip Mars upside-down).

Saturday, Sept. 5 overnight — Bright moon dances with Mars

When the bright, waning gibbous moon rises in the east at about 9:45 p.m. local time on Saturday, Sept. 5, it will be positioned only a finger’s width to the right (or 1 degree to the celestial southwest) of Mars. That’s close enough to appear together in binoculars and telescopes at low magnification (red circle). As the duo crosses the sky together during the night, the diurnal rotation of the sky, and the moon’s eastward orbital motion, will combine to shift the moon clockwise around Mars — placing it above the planet by sunrise on Sunday morning. Since the pair will not set in the west until mid-morning on the 6th — skywatchers have a chance to see Mars in the morning daytime sky using binoculars and backyard telescopes — by using the moon as a reference. Observers in central and northeastern South America, Cape Verde Islands, northern Africa, and southern Europe will see the moon occult Mars around 05:00 GMT on Sunday.

Sunday, Sept. 6 overnight — Gibbous moon and Uranus

When the bright, waning gibbous moon rises in the east at about 10 p.m. local time on Sunday, Sept. 6, it will be positioned several finger widths to the lower right (or 4 degrees to the celestial south) of blue-green Uranus. That magnitude 5.71 planet is visible in binoculars (red circle) and backyard telescopes — if you know where to find it. This bright moon will be too bright for dim-planet hunting. Note the positions of the brighter stars in Cetus (below the moon) and Aries (above Uranus), and use them to find Uranus on a night when the moon isn’t nearby.

Wednesday, Sept. 9 all night — Mars Stands Still

On Wednesday, Sept. 9, Mars will cease its eastward motion through the distant background stars of Pisces, and commence a retrograde loop (red path with labeled dates) that will last through opposition in October, and end in mid-November. To see Mars’ motion, note its position compared to the stars around it and check back on subsequent evenings to see the difference.

Thursday, Sept. 10 at 9:26 GMT — Last quarter moon

At its last quarter phase at 9:26 GMT on Thursday, Sept. 10, the moon will rise around midnight and remain visible in the southern sky all morning. At this phase, the moon is illuminated on its western side, towards the pre-dawn sun. Last quarter moons are positioned ahead of the Earth in our trip around the sun. About 3½ hours later, Earth will occupy that same location in space. The week of moonless evening skies that follow last quarter will be ideal for observing deep sky targets.

Friday, Sept. 11 post-midnight — Crescent moon meets Messier 35

When the waning crescent moon rises shortly after 12 a.m. local time on Friday, Sept. 11, it will be positioned several degrees to the celestial west of the large open star cluster in Gemini known as Messier 35 or the Shoe-Buckle. During the rest of the night, the moon’s orbital motion (green line) will carry it closer to the cluster — bringing it just a finger’s width to the right of Messier 35 before dawn. To see the cluster’s stars more easily, hide the bright moon just beyond the right edge of your binoculars’ field of view (red circle).

Friday, Sept. 11 overnight — Neptune at opposition near Phi Aquarii

On Friday, Sept. 11, Neptune will be directly opposite the sun in the sky. At opposition, Neptune will be closest to us for this year — 4 light-hours or 28.9 Astronomical Units from Earth. It will shine at a slightly brighter magnitude 7.8, and will be visible all night long in good binoculars (red circle) and backyard telescopes in a dark sky. Around opposition, Neptune’s disk size will grow to 2.4 arc-seconds. Throughout September, Neptune will be located among the stars of northeastern Aquarius, about two degrees to the left (or celestial east) of the naked-eye star Phi (φ) Aquarii.

Saturday, Sept. 12 evening — Jupiter completes its retrograde loop

On Saturday, Sept. 12, Jupiter will appear to stop moving with respect to the distant stars — marking the end of a westward retrograde loop (red path with labelled dates:times) that began in mid-May. After tonight, Jupiter will resume its regular eastward motion in northeastern Sagittarius, and will begin to reduce its 8-degree separation from Saturn.

Sunday, Sept. 13 at 9:08 p.m. EDT — Algol at minimum brightness

Algol, also designated Beta Persei, is among the most accessible variable stars for skywatchers. Its naked-eye brightness dims noticeably for about 10 hours once every 2 days, 20 hours, and 49 minutes because a dim companion star orbiting nearly edge-on to Earth crosses in front of the much brighter main star, reducing the total light output we receive. On Sunday, Sept. 13 at 9:08 p.m. EDT (or 1:08 GMT on Monday), Algol will reach its minimum brightness of magnitude 3.4. At that time, for observers in the Eastern time zone, the star will sit 12 degrees above the northeastern horizon. Five hours later, at 2:08 a.m. EDT (or 6:08 GMT), Algol will be high in the eastern sky, and will have brightened to its usual magnitude of 2.1.

Monday, Sept. 14 pre-dawn — Old moon meets Venus near M44

When the waning crescent moon rises at about 3:15 a.m. local time on Monday, Sept. 14, it will be positioned a few finger widths to the left (or 4 degrees to the celestial north) of the bright planet Venus. The pair, which will remain visible in the east until sunrise, will fit together into the field of view of binoculars (red circle) and will make a lovely wide-field photograph when composed with some interesting landscape. Your binoculars might also reveal the large open star cluster known as the Beehive or Messier 44, sitting just above and between the moon and Venus. To see the cluster’s stars more easily, hide the moon and Venus just below your binoculars’ field of view.

Monday, Sept. 14 at 6:57 GMT — Rare double shadow transit with GRS on Jupiter

From time to time, the Great Red Spot (GRS) and the little round, black shadows cast by Jupiter’s four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet’s disk. Commencing a few minutes before midnight on Sunday night, and continuing during the wee hours of Monday, Sept. 14, observers on the west coasts of the USA and Canada, and the Pacific Ocean, can witness the rare event of a double shadow transit — accompanied by the Great Red Spot! At 11:57 p.m. PDT (or 06:57 GMT) Ganymede’s larger shadow and the Great Red Spot will join Io’s smaller shadow already progressing across Jupiter’s disk. The trio will remain visible until Io’s shadow moves off Jupiter at about 1:30 a.m. PDT (or 08:30 GMT). In some regions Jupiter will set during the event, but observers in the Pacific Ocean region can see the entire transit.

Wednesday, Sept. 16 pre-dawn — Morning zodiacal light for mid-northern observers

For about half an hour before dawn during moonless periods in September and October annually, the steep morning ecliptic favors the appearance of the zodiacal light in the eastern sky. This is sunlight scattered by interplanetary particles concentrated in the plane of the solar system. During a two-week period that starts just before the September new moon, look above the eastern horizon for a broad wedge of faint light rising from the horizon and centered on the ecliptic (marked by a green line), which extends below Venus toward the bright star Regulus in Leo. Don’t confuse the zodiacal light with the Milky Way, which is positioned further to the southeast.

Thursday, Sept. 17 at 11:00 GMT — New moon

At its new phase, the moon is travelling between Earth and the sun. Since sunlight is only reaching the far side of the moon, and the moon is in the same region of the sky as the sun, the moon will be completely hidden from view for about a day. Since this new moon is occurring a day before perigee, the moon’s minimum distance from Earth, tides will be larger around the world.

Friday, Sept. 18 after sunset — Crescent moon and Mercury

After sunset on Friday, Sept. 18, sharp-eyed observers might spot the very slim crescent moon sitting just above the western horizon, and a slim palm’s width to the upper right (or 5 degrees to the celestial north) of Mercury. The moon and Mercury will both fit into the field of view of binoculars (red circle) — but ensure that the sun has completely disappeared from view before using them.

Monday, Sept. 21 after sunset — Mercury moves past Spica

Low in the west-southwestern sky after sunset on Monday, Sept. 21, Mercury’s rapid orbital motion (red curve) will bring it very close to Spica, Virgo’s brightest star. Look for brighter Mercury sitting just 40 arc-minutes (about 1.3 times the diameter of a full moon) to Spica’s right (celestial west), allowing both objects to fit into the field of view of a backyard telescope at medium magnification. On the following evening, Mercury will climb to sit a similar distance above Spica. Observers viewing from southerly latitudes will be able to see the duo more easily.

Tuesday, Sept. 22 pre-dawn — Venus passes Vesta

In the eastern pre-dawn sky on the mornings surrounding Tuesday, Sept. 22, very bright Venus will overtake and pass the slower-moving main belt asteroid Vesta. Venus will be dropping sunward while Vesta climbs in the opposite direction. At closest approach on Tuesday morning, Venus will be positioned about two finger widths to the right (or 2 degrees to the celestial south) of Vesta. Magnitude -4.14 Venus will outshine magnitude 8.16 Vesta by more than 8300 times! To see how both objects move compared to the stars around them, try to view the event on several mornings — ideally before 6 a.m. local time, when the sky will be starting to brighten.

Tuesday, Sept. 22 at 13:31 GMT — Equinox

On Tuesday, Sept. 22 at 13:31 GMT, the sun will cross the celestial equator moving southward, marking the autumnal equinox in the Northern Hemisphere and the beginning of autumn there. On the equinoxes in March and September, day and night are of equal length and the sun rises due east and sets due west.

Wednesday, Sept. 23 at 9:55 p.m. EDT — First quarter moon

When the moon completes the first quarter of its orbit around Earth at 9:55 p.m. EDT on Wednesday, Sept. 23 (or 1:55 GMT on Thursday, Sept. 24), the relative positions of the Earth, sun, and moon will cause us to see it half-illuminated — on its eastern side. At first quarter, the moon always rises around noon and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings surrounding first quarter are the best ones to see the lunar terrain when it is dramatically lit by low-angle sunlight.

Thursday, Sept. 24 evening — Gibbous moon near Jupiter

The moon’s monthly visit with the gas giant planets Jupiter and Saturn will commence on the evening of Thursday, Sept. 24. As the evening sky darkens, the bright planet Jupiter will become visible several finger widths to the upper left (or 4.5 degrees to the celestial northeast of) the gibbous moon in the southern sky. The moon and Jupiter will fit into the field of view of binoculars (red circle). Look for somewhat dimmer Saturn sitting off to their upper left (east). By the time they set soon after midnight local time, the moon will slide east, closer to Jupiter — and the diurnal rotation of the sky will raise Jupiter above the moon. This conjunction will make a beautiful wide field image when composed with some interesting foreground scenery.

Friday, Sept. 25 evening — Bright moon below Saturn

The moon’s monthly visit with the gas giant planets Jupiter and Saturn will continue on Friday, Sept. 25. After 24 hours of eastward motion, the bright waxing moon will sit several finger widths to the lower left (or 3.6 degrees to the celestial south of) yellowish Saturn in the southern sky after dusk. The moon and Saturn will fit into the field of view of binoculars (red circle). Look for much brighter Jupiter sitting to their right (west). By the time the moon and Saturn set shortly before 1 a.m. local time, the moon will be farther from Saturn — and the diurnal rotation of the sky will lower Saturn to the moon’s right. This conjunction will make a beautiful wide field image when composed with some interesting foreground scenery.

Sunday, Sept. 27 all night — Sinus Iridum’s Golden Handle

On Sunday night, Sept. 27, the terminator on the waxing gibbous moon will fall just west of Sinus Iridum, the Bay of Rainbows. The circular 155 mile (249 km) diameter feature is a large impact crater that was flooded by the same basalts that filled the much larger Mare Imbrium to its east — forming a rounded handle-shape on the western edge of that mare. The “Golden Handle” effect is produced by way the slanted sunlight brightly illuminates the eastern side of the prominent Montes Jura mountain range surrounding the bay on the north and west, and by a pair of protruding promontories named Heraclides and Laplace to the south and north, respectively. Sinus Iridum is almost craterless, but hosts a set of northeast-oriented dorsae or “wrinkle ridges” that are revealed at this phase.

Tuesday, Sept. 29 evening — Saturn stands still

On Tuesday, Sept. 29, Earth’s faster orbit will cause Saturn to appear to stop moving with respect to the distant stars. The temporary pause in motion (red path with labelled dates:times) marks the end of a westward retrograde loop that began on May 11. After dusk, look for the yellowish, magnitude 0.46 planet in the lower part of the southern sky among the stars of northeastern Sagittarius — seven degrees east of much brighter Jupiter.

Planets

During September, Mercury will steadily swing away from the sun in the western evening sky. Due to the shallow angle of the evening ecliptic, Mercury will remain very close to the horizon for observers at mid-northern latitudes. Those viewing the swift planet from the southern USA will see Mercury more easily — higher, and in a darker sky — especially after the first week of the month. Meanwhile, observers located near the equator and in the Southern Hemisphere will get their best look at Mercury for 2020. Viewed in a telescope during September, Mercury will wane in phase from 91% to 77% illuminated, and the planet’s apparent disk size will increase by about 20%. After sunset on Sept. 18, the very slim crescent moon will sit a slim palm’s width to the upper right (or 5 degrees to the celestial north) of Mercury.

During September, Venus will continue to rise during the wee hours and shine very brightly in the eastern pre-dawn sky. Meanwhile it will be slowly moving sunward — shifting from Gemini into Cancer on Sept. 4 — and then, for the final week of September, through western Leo. Venus will end the month near Leo’s brightest star Regulus. (Venus will pass very close to Regulus on October 2-3.) During September, Venus will diminish slightly in visual brightness. Viewed in a telescope, the planet will exhibit a waning gibbous phase, and an apparent disk size that shrinks from 19.5 to 15.6 arc-seconds. On the mornings surrounding Sept. 13, Venus will pass just to the lower right (or 2 degrees to the celestial south) of the large open star cluster Messier 44 in Cancer. The old crescent moon will join them on the 14th. On the mornings surrounding Sept. 22, Venus will overtake and pass within 2 degrees of the slower main belt asteroid Vesta.

Mars will become a prime target for skywatchers during September — a dress rehearsal for its big opposition event in mid-October — the best in the 2020’s. As the month opens, the red planet will rise shortly before 10 p.m. local time and cross the overnight sky as a -1.83 object among the stars of southern Pisces. On Sept. 9, Mars will cease its regular eastward motion and commence a retrograde loop that will last until mid-November. That reversal will keep the planet within the V of Pisces all month long. By month-end, much brighter (magnitude -2.5) Mars will rise during dusk and invite telescope views all night long, especially after midnight, when it will climb higher in the sky for mid-northern observers. During September, Mars’ apparent disk size will increase from 19 to 22.5 arc-seconds and its phase will grow to almost fully-illuminated. Since Mars’ solstice occurs on Sept. 3, the planet’s bright southern polar cap will be tipped towards Earth — shrinking as it warms, but still prominent in telescopes. On Sept. 5-6, the bright, waning gibbous moon will pass only 1 degree to the southwest of Mars. Observers in central and northeastern South America, Cape Verde Islands, northern Africa, and southern Europe will see the moon occult Mars around 05:00 GMT on Sept. 6. Since the pair will not set in the west until mid-morning on the 6th — skywatchers have a chance to see Mars in the morning daytime sky using binoculars and backyard telescopes — by using the moon as a reference.

During September, Jupiter will continue to be well-placed for evening observing in the lower part of the southwestern sky. The earlier sunsets of autumn will keep Jupiter in sight, even as it slides farther into the west every night. In early September, Jupiter will already be shining in the lower part of the southern sky as dusk begins — with nearby, dimmer Saturn appearing soon afterward. On Sept. 13, Jupiter will complete a retrograde loop that began in mid-May, and resume its regular eastward motion through the stars of eastern Sagittarius. From that point on, Jupiter’s faster orbit will cause it to diminish its angular separation from slower Saturn. During September, Jupiter will drop slightly in brightness — from magnitude -2.55 to -2.35. Its apparent disk diameter will shrink from 44 To 40 arc-seconds. On Sept. 14 at 06:57 GMT Ganymede’s larger shadow and the Great Red Spot will join Io’s smaller shadow already progressing across Jupiter’s disk. The trio will remain visible until Io’s shadow moves off Jupiter at about 08:30 GMT. On Sept. 24 the waxing gibbous moon will sit to the celestial southwest of Jupiter and Saturn — a grouping that will make a beautiful wide field image.

Like nearby Jupiter, Saturn will be well-positioned for evening observing during September — although they will remain rather low in the sky for mid-Northern observers. The ringed planet will move retrograde (westward) through the stars of northeastern Sagittarius until Sept. 29, and then resume regular prograde motion — allowing faster Jupiter to move closer to it during autumn. The rings, and many of Saturn’s moons, are easily visible in backyard telescopes. During September, Saturn will diminish slightly in apparent size, and dim from magnitude 0.3 to 0.4. On Sept. 25, the waxing gibbous moon will sit 3.6 degrees to the south of Saturn. With Jupiter positioned nearby, the scene will make a beautiful wide field image.

During September, blue-green Uranus (magnitude 5.7) will transition from a late-night object to an evening object — eventually rising at 8 p.m. local time by month-end. The planet will be traveling slowly westward in southwestern Aries. Find it 11 degrees south of Aries’ brightest star Hamal, or 5 degrees north of the stars that form the top of Cetus’ head. On Sept. 6, the waning gibbous moon will be positioned 4 degrees south of Uranus.

Neptune will be visible all night during September — moving retrograde (westward) among the stars of eastern Aquarius. On Sept. 11, Neptune will reach opposition. At that time, the blue-tinted planet will be 4 light-hours or 28.9 Astronomical Units from Earth, it will shine at a slightly brighter magnitude 7.8, and will be visible all night long in good binoculars and backyard telescopes in a dark sky. Around opposition, Neptune’s disk size will grow to 2.4 arc-seconds. Throughout the month, the planet will be creeping toward that constellation’s naked-eye star Phi (φ) Aquarii, located about two degrees to Neptune’s west.

Skywatching Terms

Gibbous: Used to describe a planet or moon that is more than 50% illuminated.

Asterism: A noteworthy or striking pattern of stars within a larger constellation.

Degrees (measuring the sky): The sky is 360 degrees all the way around, which means roughly 180 degrees from horizon to horizon. It’s easy to measure distances between objects: Your fist on an outstretched arm covers about 10 degrees of sky, while a finger covers about one degree.

Visual Magnitude: This is the astronomer’s scale for measuring the brightness of objects in the sky. The dimmest object visible in the night sky under perfectly dark conditions is about magnitude 6.5. Brighter stars are magnitude 2 or 1. The brightest objects get negative numbers. Venus can be as bright as magnitude minus 4.9. The full moon is minus 12.7 and the sun is minus 26.8.

Terminator: The boundary on the moon between sunlight and shadow.

Zenith: The point in the sky directly overhead.

Night Sky Observing Tips

Adjust to the dark: If you wish to observe faint objects, such as meteors or dim stars, give your eyes at least 15 minutes to adjust to the darkness.

Light Pollution: Even from a big city, one can see the moon, a handful of bright stars and sometimes the brightest planets. But to fully enjoy the heavens — especially a meteor shower, the constellations, or to see the amazing swath across the sky that represents our view toward the center of the Milky Way Galaxy — rural areas are best for night sky viewing. If you’re stuck in a city or suburban area, a building can be used to block ambient light (or moonlight) to help reveal fainter objects. If you’re in the suburbs, simply turning off outdoor lights can help.

Prepare for skywatching: If you plan to be out for more than a few minutes, and it’s not a warm summer evening, dress warmer than you think necessary. An hour of observing a winter meteor shower can chill you to the bone. A blanket or lounge chair will prove much more comfortable than standing or sitting in a chair and craning your neck to see overhead.

Daytime skywatching: When Venus is visible (that is, not in front of or behind the sun) it can often be spotted during the day. But you’ll need to know where to look. A sky map is helpful. When the sun has large sunspots, they can be seen without a telescope. However, it’s unsafe to look at the sun without protective eyewear. See our video on how to safely observe the sun, or our safe sunwatching infographic.