Transient Events That Can Give Us a Good Enough Reason to Get Outside and Do a Little Observing
September 2026
All month: in the evening sky, Venus and Mercury are challenging targets near sunset, while Neptune and Saturn liven up the later evening scene, and Uranus follows not too far behind them. Meanwhile, Jupiter climbs out of the Sun’s glare to join Mars in the early morning time slot. Mercury emerges into the sunset sky following its Aug 27 conjunction, but our view is impeded by the flat evening ecliptic, which keeps the planet close behind the Sun all month. It sets just 30 minutes after sunset on Sept 13, and 42 minutes after sunset on Sept 30, when it will show us a 6 arcsecond gibbous disk shining at mag -0.1. Venus is in the final weeks of its long evening apparition, setting 82 minutes after the Sun as the month begins but only 36 minutes after sunset as it ends. Its disk swells from 30 to 47 arcseconds during the month as its illuminated portion shrinks from 39% to 16%, giving it a wonderful crescent shape by Sept 10. It blazes at mag -4.6 on Sept 1, reaches greatest brilliancy at mag -4.8 on Sept 18, and finishes September at mag -4.7. As Venus drops below the horizon in the west, Neptune rises in the east, peeking over Earth’s edge a few minutes before 8:30 pm as the month begins and two hours earlier as it ends, its 2½ arcsecond blue disk glowing at a binocular-friendly mag 7.8. It reaches opposition on Sept 25, overwhelmed by a nearly-full moon 9° away. Saturn rises a half hour later, its 20 arcsecond disk brightening from mag +0.5 to +0.3 as it rushes towards opposition on Oct 4. The rings tilt 8° to our perspective, exposing the planet’s south polar region. Uranus is the next planet to rise, at 11 pm as September begins and 9:05 pm as it ends. Its blue-green disk sits between the Hyades and the Pleiades all month. It measures 4 arcseconds and shines at mag 5.7, teasing the edge of naked eye visibility if you’re at a dark site. All three of the late evening planets stay up past sunrise, giving the morning people plenty to look at. The morning show is augmented by Mars, which rises around 1:30 am on Sept 1 and a half hour earlier on Sept 30, its 5 arcsecond disk brightening from mag +1.3 to +1.1 but still too small for meaningful observation of surface details. The last planet up is Jupiter, crossing the horizon a few minutes after 4 am as the month begins and at 2:40 am as it ends, brightening from mag -1.8 to -1.9 as its disk grows slightly, from 32 to 33 arcseconds. It’s a busy month among the asteroids, with 192 Nausikaa reaching opposition at mag 8.4 on Sept 30, and a pair of big ones – 2 Pallas and 4 Vesta – lit up like beacons as they head toward their own oppositions in October. This month’s charts will help you find them.
Sept 6 and 7: if you’re up very late or very early either of these mornings, look to the east for a color-contrast pairing of Mars and the crescent Moon, framed by the stars of the Winter Hexagon. The duo crosses the horizon by 1:30 am CDT on the 6th, with Mars chasing the Moon across the sky, and by 2:00 am on the 7th, when it’s the Moon’s turn to do the chasing. Neither of them ever catches the other, and morning twilight erases the scene around 6 am.
Sept 8: the Moon occults Jupiter in daylight this afternoon. Both the disappearance and reappearance happen just 30° from the Sun: be sure to use solar precautions, and observe from a shaded spot so the
obstruction that produces the shade stands between the Sun and your eyes. Start watching no later than 1:45 pm CDT. First find the narrow crescent Moon (only 7% illuminated) 45° above the WSW horizon and 30° right of the Sun. Use binoculars if you can’t spot it naked-eye – you’ll need them (or probably a telescope) in any event, to see the planet’s disappearance. Jupiter is the tiny bright dot (mag -1.8) just to the left of the Moon, near the middle of its bright limb. It arrives at the edge at 1:50 pm and will take more than a minute to slowly slip behind the lunar disk. An hour later, at 2:51 pm, watch the middle of the Moon’s dark edge to spot the planet slowly peek out and emerge from hiding.
Sept 11: if you observed any of the Titan shadow transits last Fall (or if you’re kicking yourself because you missed them all), get your largest aperture scope – at least 8” but preferably more – crank up the power to at least 200x, and try for a shadow transit of Saturn’s mag 10.4 moon Dione late tonight. The little moon, only 700 miles wide, casts its shadow across the planet’s northern edge from 1:05 to 2:30 am CDT, moving from east to west, although your best chance of seeing it will be between 1:30 and 2:00 am when it’s near Saturn’s meridian. Dione itself skims along the very edge of the planet, so close to its north limb that it’s difficult to spot from 1:20 to 2:45 am. Meanwhile, Saturn’s mag 10.2 moon Tethys slips into Saturn’s shadow SW of the planet at 1:10 am, and slides behind the planet’s disk at 1:26 am.
Sept 13: new moon arrived at 10:27 pm CDT on Sept 10, and set less than 30 minutes after the Sun on Sept 11 and 12, but at 7:35 pm tonight (a half hour after sunset) it will be 9% illuminated, 3½° above the horizon, and 30° left of the spot where the Sun went down. If you can’t find it at first, look 5½° below right of brilliant mag -4.7 Venus. If you miss it tonight, try tomorrow, when the 16% illuminated crescent will be 5½° left and slightly above Venus. For a twilight observing challenge, see if you can spot mag 1.0 Spica (Alpha [] Virginis) either night, 8½° directly to the right of Venus, at the same elevation.
Sept 17: the Moon, a day before first quarter, chases 5° behind Antares (Alpha [] Scorpii) tonight. Be sure to catch the color contrast before they both set around 10 pm CDT.
Sept 19: the Moon, now a day past first quarter, poses inside the Teapot of Sagittarius as it makes a brief low pass along the south side of the sky, reaching only 20° elevation and setting before midnight.
Sept 22: the autumnal equinox arrives at 7:05 pm CDT, nailing the lid on another summer, and promising longer nights to come. Later, mag 5.4 star 30 Capricorni slips behind the dark edge of the 86% lit gibbous Moon at 8:40 pm, followed by mag 4.3 Iota () Cap at 12:34 am.
Sept 23: it’s another occultation late tonight, as the narrow dark edge of a 93% lit Moon covers up mag 5.4 star 38 Aquarii at 12:41 am CDT.
Sept 26: as the Sun sets, the full Moon rises, with Saturn following an hour later. The pair cross the sky with the planet maintaining a respectful 6° distance until it disappears in morning twilight.
Sept 30: today is the spring equinox for the northern hemisphere on Mars, which also marks the Martian new year (see https://www.planetary.org/articles/mars–calendar if you don’t believe me). Celebrate in whatever way you think best.
Rick Gering / September 2026