The sky at dusk on Sept. 1 features the moon crossing just 21° above the southern horizon, 5° lower than the midday sun on the winter solstice, Dec. 21.
The brightest stars in September’s evening twilight are Arcturus, well up in the west, and Vega, nearly overhead. Altair and Deneb complete the Summer Triangle with Vega. Look for the first-magnitude zodiacal stars Antares in the south-southwest, 20° west of the moon on Sept. 1, and Spica in the west-southwest, 33° to the lower left of Arcturus. Fainter, 1.6-magnitude Mars on Sept. 1 is 8° to the lower right of Spica and closing the gap between them by 0.6° per day. On Sept. 12 and 13, use binoculars to watch Mars pass 2.2° above Spica in the twilight glow.
At the start of September, you must wait until nightfall, when full darkness descends, to catch Saturn a few degrees above the horizon, just south of due east. For an excellent view, wait another 4 1/2 hours until Saturn ascends to a position high in the south-southeast, about an hour before Saturn reaches its high point directly south. Aim binoculars at the 0.7-magnitude planet, and you will then notice, in the same field below it, four stars forming an approximate rectangle, just less than a degree wide, with its vertical, longer sides nearly 3 degrees tall. Both top stars of the rectangle are near magnitude 5.0, and the two lower stars shine near magnitude 4.5. These four stars mark the shell of now-obsolete asterism Testudo, the Turtle. Two additional stars extending in a straight line from the upper right corner of the rectangle, of magnitude 5.9 and 5.5, define the Turtle’s neck and head. In 1754, the British botanist and author John Hill selected these stars in Pisces to form a new constellation, Testudo (the Turtle). The proposal was largely ignored by astronomers.
It’s time to bring back the Turtle! You can easily notice the motion of Saturn against the background of the Turtle asterism. On morning of Sept. 7, Saturn passes within 0.5 north of 29 Piscium, marking the northeast (upper left) corner of the rectangle. On the morning of Sept. 14, Saturn forms an isosceles triangle with the top stars of the rectangle, and you can use these stars to find faint Neptune nearby, as described below. On the morning of Sept. 19, Saturn passes 0.6° north of 27 Psc at the northwest (upper right) corner of the rectangle.
On Sept. 7, the moon, full earlier that day, rises shortly after sunset, with Saturn following 8° or 9° to the moon’s lower left. The next evening, Saturn and the moon rise more or less together, with the moon about 7° to Saturn’s left. These nights with a bright moon nearby are not good for seeing the Turtle! For several evenings, the moon comes up farther north and not much later each evening—the harvest moon effect! Wait until at least Sept. 12 for a good look at the Milky Way in a dark evening sky for a short while after evening twilight ends.
September’s morning planets: About one hour before sunrise, Venus, shining at magnitude -4 in the east, begins this month 17° up, and drops 5° lower by month’s end. Jupiter, of magnitude -2, is in the east to east-southeast, to the upper right of Venus, by 20° on Sept. 1, increasing to 51° by Sept. 30. Venus in September moves east against background stars by about 1.2° per day, compared to Jupiter’s eastward crawl of 11’ (arcminutes) to 7’ (0.18° to 0.12°) per day. The other bright planet in the morning sky is Saturn, of magnitude +0.7 to +0.6, sinking through the west-southwest toward the western horizon as the month progresses. At opposition as Earth overtakes it on night of Sept. 20-21, Saturn sets 45 minutes before sunrise at month’s end. Saturn is also visible in the evening, rising within an hour after sunset on Sept. 1, and within a few minutes of sunset on the 20th.
On Sept. 14, one hour and 40 minutes before sunrise, the last quarter moon will be almost directly ahead of Starship Earth. Also on Sept. 14, we have a panoramic view of the four giant planets spread out in a 111° arc ahead of us, and we’ll overtake each in turn within an interval of 111 days: Saturn on the night of Sept. 20, Neptune on Sept. 23, Uranus on Nov. 21, and Jupiter on Jan. 9, 2026.
Use binoculars before twilight to locate 5.7-magnitude Uranus, 4.4° south of 2.9-magnitude Alcyone, or Eta Tauri, the Pleiades’ brightest star. It’s helpful to first locate the pair of stars 13 and 14 Tauri (magnitude 5.7 and 6.1), 21’ (arcminutes) or 0.35° apart, 4.5° to 4.6° south and slightly west of Eta Tauri. On Sept. 14, Uranus is 2.9° to 3.2° east of the pair. At magnitude 5.7, 13 Tauri is a close match to Uranus in brightness.
Neptune on Sept. 14 is just 2.3° from Saturn. First note the two fifth-magnitude stars 27 and 29 in Pisces (the top of the rectangle marking the Turtle’s shell), 0.95° apart and each about 0.7° from Saturn, forming an isosceles triangle. The star 29 Psc is the one farther east. The 6.3-magnitude star HIP 417, 2.65° north-northeast of 29 Psc, is a good stepping stone to Neptune. On Sept. 2, Neptune passes 0.4 south-southeast of HIP 417. On Sept. 29, magnitude 7.8 Neptune is 0.5° south and slightly west of HIP 417, almost on the line back toward 29 Psc.
Return your attention to Venus, and note the star Regulus 6° to its lower left on Sept. 14. With Venus included, the arc of five morning planets expands to 145°.
Follow the moon in the morning sky Sept. 7-20. Catch the waning moon near Saturn on Sept. 8 and 9; near the Pleiades cluster Sept. 12; widely north of Aldebaran and the Hyades cluster on Sept. 13; and very near 1.7-magnitude Elnath or Beta Tauri, tip of the northern horn of the Bull, on Sept. 14.
On the morning of the 16th, the waning crescent moon will appear near Jupiter, Pollux and Castor, and on the 17th, near the Beehive cluster (use binoculars). On Sept. 18, the moon will appear 11°-12° above the closing Venus-Regulus pair.
Regulus will appear 0.5° to the lower right of Venus on Sept. 19, while the moon stands about one degree to the lower left of Venus. That’s a 6 percent waning crescent moon with earthshine, a brilliant planet, and a star all within a field less than 2° across—a spectacular sight for the unaided eye, binoculars and telescope! Don’t miss it!
The waning moon will appear for one additional morning, Sept. 20. Look for the 2 percent crescent rising in twilight, 12°-13° to the lower left of Venus. Regulus will then appear 1.1° to the bright planet’s upper right.
The moon returns to the evening sky on Sept. 23, when the 5-percent crescent will be very low in bright twilight, within 3° to the lower left of Spica and 6° to the lower right of Mars. This may require binoculars, and for observers farther north, it will be an even more difficult challenge. On the next evening, the 10 percent crescent will be 8° to the left of Mars. On Sept. 26, the crescent will be 8° to the lower right of Antares, and on the next evening, the 32 percent crescent will be 4° left of Antares.
On Sept. 28, this month’s second far southern moon appears 16° to the east (left) of Antares. On the last two evenings of September, the moon appears in the constellation Sagittarius—on the 29th within, and on the 30th east of, the asterism of the Teapot.
Saturn on Sept. 30 at dusk can be spotted low in east to east-southeast. We must wait until Oct. 5 until the nearly full moon pulls alongside it.
Robert Victor originated the Abrams Planetarium monthly Sky Calendar in October 1968 and still helps produce an occasional issue. He enjoys being outdoors sharing the beauty of the night sky and other wonders of nature.
