September brings a very good opportunity to sight the so-called "elusive" planet Mercury. Normally positioned too low to the horizon and mired in the glare of the sun, Mercury is favorably positioned to see low in the eastern morning sky about an hour before sunup during the first half of the month. A crescent moon will be near to this speedy little world on the 1st.
As the month progresses, another planet that is noticeably improving in visibility is orange Mars, which is slowly brightening as it approaches Earth and ascends the east-northeast sky after midnight. Jupiter gleams brilliantly against the stars of Taurus the Bull and appears in the east-northeast during the late-evening hours. Saturn is positioned directly opposite to the sun in the sky early in the month and as a result is in the night sky all night long.
Ironically, the most difficult planet to sight this month is by far the brightest: Venus. It's now an "evening star," but hangs very low to the western horizon and disappears only about an hour after sundown.
Related: Night sky, September 2024: What you can see tonight [maps]
Read more: Best telescopes for seeing planets in 2024
Looking for a telescope to see the planets in June? We recommend the Celestron Astro Fi 102 as the top pick in our best beginner's telescope guide.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm's length measures roughly 10 degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Be sure to check out our best telescopes for viewing planets guide and our more general guides for the best binoculars and the best telescopes. If you're interested in taking your own impressive skywatching images, we have recommendations for the best cameras for astrophotography and the best lenses for astrophotography.
The sun
The sun arrives at the September equinox on Sept. 22 at 8:44 a.m. EDT (1244 GMT), heading south across the celestial equator. This event marks the start of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.
Mercury
Mercury starts the month as a +0.5-magnitude "star" rising in the east-northeast shortly after morning twilight begins; it's near the peak of a brief but relatively high leap into the dawn sky in early September. About 45 minutes before sunrise on Sept. 1, look for a razor-thin waning crescent moon (just 2% illuminated) sitting 4½-degrees to the upper left of Mercury.
The speedy little planet stands 18-degrees west of the sun on Sept. 4. This is the minimum value for a greatest elongation, yet the apparition is favorable for mid-northern observers because the ecliptic is nearly perpendicular to the horizon. Mercury rises about 1½ hours before the sun and attains an altitude of 8-degrees in mid-twilight. On Sept. 9 Mercury, now at magnitude -0.8, stands almost 10-degrees above the eastern horizon a half hour before sunup.
That's good, because Mercury is only a mere half-degree to the left of the much fainter star, Regulus. Binoculars will probably be needed to see the +1.3-magnitude star that low in bright twilight. Mercury appears markedly lower each morning after that that. It continues to brighten rapidly, reaching a brilliant magnitude of -1.2 by the 15th, but by then it's quickly sinking back down. Thereafter, Mercury leaves the morning sky as it heads toward superior conjunction (beyond the sun) on the 30th.
Venus
Venus begins September only 5-degrees above the western horizon, 30 minutes after sunset for viewers at mid-northern latitudes. But even by the end of September this planet is still very low at dusk. On the evening of Sept. 5, look well to the left of Venus to also catch sight of a slender waxing crescent moon.
Mars
Mars starts September in Taurus about nine degrees east of Jupiter, and then crosses over into Gemini the Twins on Sept 6. It rises in the middle of the night but is best seen at dawn's first light, when it shines high in the east-southeast predawn sky. It brightens slightly from magnitude +0.7 to +0.5 in September, and on the morning of Sept. 25 it can be found about 5-degrees to the lower right of the moon.
Jupiter
Jupiter is placed amidst a splendidly rich and bright field of stars. Shining at a dazzling magnitude -2.4, Jupiter is found a few degrees to the west of the horn tips of Taurus the Bull and soaring high above Orion the Hunter.
The best telescopic views of Jupiter's intricate details of cloud bands and four largest moons, the Galilean satellites, come after midnight or, best of all, when it is very high around morning twilight. On Sept. 23, the big planet rises north of east around 10:30 p.m. local daylight time, well to the right of a waning gibbous moon.
Saturn
Saturn reaches opposition on Sept. 8 and shines at magnitude +0.6 for most of the month. It's always the favorite planet to show the public through telescopes at star parties, and September finds it visible all night at its closest and biggest of the year. Look for Saturn low in the east-southeast in twilight.
As night deepens, you'll see that this lovely world stands awesomely alone in the midst of the faint stars of Aquarius the Water Carrier. It's fairly high in the south by midnight and its flattened globe currently appears only about half as wide as Jupiter's, but its rings spread wider than Jupiter. They are tilted only about 4° from edge on, though.
At nightfall on Sept'' 16, low in the east-southeast, take note of Saturn positioned about a half-dozen degrees to the left of the nearly full moon. During the course of the overnight hours, the moon will slowly glide toward Saturn at a rate of roughly its own diameter per hour. By dawn the following morning, the moon and Saturn will be separated by less than two degrees.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications.
Editor's Note: If you get a great photo of any of the planets and would like to share it with Space.com's readers, send your photo(s), comments, and your name and location to spacephotos@space.com.
Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.
