September 2021 Celestial Calendar by Dave Mitsky
All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
9/1 The equation of time, which yields the difference between mean solar time and apparent solar time, equals 0 at 8:00; the Moon is 1.4 degrees north of the bright open cluster M35 in Gemini at 11:00
9/2 The Moon is 6.6 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 23:00
9/3 The Moon is 3.0 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 5:00
9/4 The Moon is 3.1 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 7:00
9/5 Venus is 1.6 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 21:00
9/6 The Moon is 4.5 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 0:00; Mercury is at aphelion (0.4667 astronomical units from the Sun) at 0:00
9/7 New Moon (lunation 1221) occurs at 0:51; the Moon is 3.8 degrees north-northeast of Mars at 20:00
9/9 The Moon is 5.9 degrees north-northeast of Mercury at 2:00; the Moon is 5.3 degrees north-northeast of Spica at 22:00
9/10 The Moon is 3.7 degrees north-northeast of Venus at 6:00
9/11 Asteroid 2 Pallas (magnitude +7.8) is at opposition in Pisces at 2:00; the Moon is at perigee, subtending 32' 26" from a distance of 368,462 kilometers (228,951 miles), at 10:03
9/12 The Moon is at descending node (longitude 244.7 degrees) at 17:00
9/13 The Moon is 4.1 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 3:00; the Lunar X, also known as the Werner or Purbach Cross, an X-shaped clair-obscur illumination effect involving various ridges and crater rims located between the craters La Caille, Blanchinus, and Purbach, is predicted to be visible at 22:08; First Quarter Moon occurs at 20:39
9/14 Mercury is at greatest eastern elongation (27 degrees) at 4:00; Neptune (magnitude +7.8, angular size 2.3") is at opposition at 9:00
9/16 The Sun enters Virgo (ecliptic longitude 174.2 degrees) at 20:00
9/17 The Moon is 3.7 degrees southeast of Saturn at 5:00; Mars crosses south of the celestial equator at 20:00
9/18 The Moon 3.8 degrees southeast of Jupiter at 10:00
9/20 The Moon is 3.7 degrees southeast of Neptune at 13:00; Full Moon (known as the Barley, Corn, or Fruit Moon, and this year's Harvest Moon) occurs at 23:54
9/21 Mercury is 1.4 degrees south-southwest of Spica at 15:00
9/22 The Sun's longitude is 180 degrees at 19:22; the northern hemisphere autumnal equinox occurs at 19:22
9/24 The Moon is 1.3 degrees southeast of Uranus at 18:00
9/26 The Moon is 4.3 degrees southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 3:00; Mercury is at its southernmost latitude from the ecliptic plane (-7.0 degrees) at 6:00; the Moon is at the ascending node (longitude 63.4 degrees) at 8:00; the Moon is 6.0 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 21:00; the Moon is at apogee, subtending 29' 32" from a distance of 404,640 kilometers (251,432 miles), at 21:44
9/27 Mercury is stationary, with retrograde (westward) motion to begin, at 4:00
9/28 The Moon is 1.6 degrees north of M35 at 19:00
9/29 Last Quarter Moon occurs at 1:57; the Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to be visible at 21:48
9/30 The Moon is 6.3 degrees south of Castor at 8:00; the Moon is 2.8 degrees south of Pollux at 13:00
Jean-Dominique Maraldi discovered the globular cluster M15 on September 7, 1746. On September 11, 1746, Jean-Dominique Maraldi discovered the globular cluster M2. Nicolas-Louis de Lacaille discovered NGC 104 (47 Tucanae), the second largest and brightest globular cluster, on September 14th, 1751. William Herschel discovered the barred spiral galaxy NGC 7753 on September 12, 1784. William Herschel discovered the Saturnian satellite Mimas on September 17, 1789. Comet C/1793 S2 (Messier) was discovered by Charles Messier on September 27th, 1793. Karl Harding discovered asteroid 3 Juno on September 1, 1804. Neptune was discovered by Johann Gottfried Galle on September 23, 1846, using Urbain Le Verrier’s calculations of its position. On September 19, 1848, William Bond discovered Saturn’s fourteenth-magnitude satellite Hyperion, the first irregular moon to be discovered. On September 13, 1850, John Russell Hind discovered the asteroid 12 Victoria. E. E. Barnard discovered Jupiter’s fifth satellite, fourteenth-magnitude Amalthea, using the 36-inch refractor at the Lick Observatory, on September 9, 1892.
Only very minor meteor showers occur this month.
Information on passes of the ISS, the USAF’s X-37B, the HST, Starlink, and other satellites can be found at http://www.heavens-above.com/
The Moon is 23.3 days old, is illuminated 35.7%, subtends 29.6 arc minutes, and is located in Taurus on September 1st at 00:00 UT. The Moon is at its greatest northern declination on September 2nd (+25.9 degrees) and on September 29th (+26.0 degrees) and its greatest southern declination on September 15th (-26.0 degrees). Longitudinal libration is at a maximum of +5.2 degrees on September 20th and a minimum of -5.3 degrees on September 5th. Latitudinal libration is at a maximum of +6.6 degrees on September 19th and a minimum of -6.5 degrees on September 6th. Favorable librations for the following lunar features occur on the indicated dates: Crater Schickard on September 3rd, Lacus Spei on September 14th, Mare Humboldtianum on September 18th, and Crater Graff on September 30th. The Moon is at perigee (at a distance of distance 57.77 Earth-radii) on September 11th and at apogee (at a distance 63.44 Earth-radii) on September 26th. New Moon (i.e., the dark of the Moon) occurs on September 7th. Full Moon occurs on September 20th. Browse http://www.lunar-occ...ota/iotandx.htm for information on lunar occultation events. Visit https://saberdoesthe...does-the-stars/ for tips on spotting extreme crescent Moons and https://curtrenz.com/moon.html for Full Moon and other lunar data. Browse https://skyandtelesc...ads/MoonMap.pdf and https://nightsky.jpl...ObserveMoon.pdf for simple lunar maps. Click on http://astrostrona.pl/moon-map for an excellent online lunar map. Visit http://www.ap-i.net/avl/en/start to download the free Virtual Moon Atlas. Consult http://time.unitariu...moon/where.html for current information on the Moon and https://www.fourmila.../lunarform.html for information on various lunar features. See https://svs.gsfc.nasa.gov/4874 for a lunar phase and libration calculator and https://quickmap.lro...2vIBvAXwF1SizSg for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on https://www.calendar.../2021/september for a lunar phase calendar for this month. Times and dates for the lunar crater light rays predicted to occur this month are available at http://www.lunar-occ...o/rays/rays.htm
The zodiacal light, or the false dawn, is visible about two hours before sunrise from a dark site for two weeks beginning on September 5th. It can be seen in Leo, Cancer, Gemini, and Taurus. Articles on the zodiacal light appear at http://www.atoptics....ighsky/zod1.htm and http://oneminuteastr...zodiacal-light/
The Sun is located in Leo on September 1st. It enters Virgo on September 16th. The Sun crosses the celestial equator from north to south at 19:22 UT on September 22nd, the date of the autumnal equinox.
Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on September 1st: Mercury (magnitude -0.1, 5.9", 74% illuminated, 1.15 a.u., Virgo), Venus (magnitude -4.0., 15.1", 73% illuminated, 1.11 a.u., Virgo), Mars (magnitude +1.8, 3.6", 100% illuminated, 2.63 a.u., Leo), Jupiter (magnitude -2.9, 48.9", 100% illuminated, 4.03 a.u., Capricornus), Saturn (magnitude +0.3, 18.3", 100% illuminated, 9.06 a.u., Capricornus), Uranus (magnitude +5.7, 3.7", 100% illuminated, 19.09 a.u. on September 16th, Aries), Neptune (magnitude +7.8, 2.4", 100% illuminated, 28.92 a.u. on September 16th, Aquarius), and Pluto (magnitude +14.3, 0.1", 100% illuminated, 33.62 a.u. on September 16th, Sagittarius).
During the month of September, Mercury and Venus are located in the west, Jupiter and Saturn in the southeast, and Neptune in the east during the evening. At midnight, Jupiter and Neptune can be found in the south, Saturn in the southwest, and Uranus in the east. Uranus is in the southwest and Neptune is in the west in the morning sky.
Mercury continues a poor evening apparition for mid-northern hemisphere observers this month. The speediest planet achieves aphelion on September 6th and greatest eastern elongation on September 14th. A very thin waxing crescent Moon passes almost six degrees north of Mercury on the evening of September 8th. On September 9th, Mercury lies 13 degrees to the lower right of the waxing crescent Moon and just over three degrees above the western horizon. Mercury passes less than two degrees northeast of Spica on September 21st.
Venus sets about 30 minutes after Mercury. By month's end, Venus sets about two hours after the Sun. The brightest planet increases in brightness from magnitude -4.0 to magnitude -4.2, increases in apparent size from 15.1 arc second to 18.6 arc seconds, and decreases in illumination from 73% to 63%. Venus passes less than two degrees north of Spica on September 5th. The three-day old waxing crescent Moon passes four degrees north of Venus on September 9th.
Mars is too close to the Sun to observe this month.
Jupiter decreases in brightness from magnitude -2.9 to magnitude -2.7 and shrinks in angular diameter from 48.9 arc seconds to 46.4 arc seconds over the course of September. Jupiter passes 1.5 degrees north of the third-magnitude star Deneb Algedi on September 12th. The waxing gibbous Moon passes four degrees south of the Jupiter on September 18th. Transits by Europa, Europa's shadow, Ganymede, and eventually Ganymede's shadow take place beginning at 8:59 p.m. EDT on September 5th. This event occurs again on the night of September 12th/13th starting at 8:26 p.m. EDT. Io and Ganymede are less than six arc minutes apart at 10:20 p.m. EDT that night. Information on Great Red Spot transit times and Galilean satellite events is available on pages 50 and 51 of the September 2021 issue of Sky & Telescope and online at http://www.skyandtel...watching-tools/ and https://www.projectp...om/jeve_grs.htm
During September, Saturn fades from magnitude +0.3 to magnitude +0.5 and shrinks in apparent size from 18.3 arc seconds to 17.7 arc seconds. Its rings are tilted 19 degrees with respect to the Earth. The waxing gibbous Moon passes four degrees south of the Ringed Planet on the night of September 16th/17th. Titan, Saturn’s largest and brightest satellite, shines at magnitude +8.5. It's due north of the planet on September 3th and September 19th and due south of it on September 11th and September 27th. An eighth-magnitude field star joins Titan to Saturn's southwest on September 12th. The star lies to the southeast of the planet on September 13th. Saturn’s peculiar satellite Iapetus glows at eleventh magnitude on September 1st as it is passes 1.5 arc minutes southwest of the planet. By the time Iapetus reaches western elongation nine arc minutes due west of Saturn on September 20th, it will have brightened to about tenth magnitude. For further information on Saturn’s satellites, browse http://www.skyandtel...watching-tools/
Uranus lies halfway between the fifth-magnitude stars Omicron and Sigma Arietis at the beginning of the month. By the final day of September, it is located within 25 arc minutes of Omicron. The waning gibbous Moon passes about one degree southeast of Uranus on September 24th. Visit http://www.nakedeyep....com/uranus.htm for a finder chart. Five of the brightest Uranian satellites (Miranda, Ariel, Umbriel, Titania, and Oberon) can be located using the Sky & Telescope interactive observing tool at https://skyandtelesc...moons-ofuranus/
Neptune is located almost five degrees east of the fourth-magnitude star Phi Aquarii as September begins. The ice giant planet lies less than four degrees east of the star at the end of the month. It passes within 1.5 arc minutes of a sixth-magnitude star on September 23rd. Neptune subtends 2.3 arc seconds, shines at magnitude +7.8, and lies at a distance of 4.0 light hours when it reaches opposition on September 14th. The Full Moon passes less than four degrees southeast of Neptune on September 20th. See http://www.nakedeyep...com/neptune.htm for an online finder chart. An article on Neptune complete with a finder chart appears on pages 48 and 49 of the September 2021 issue of Sky & Telescope. Triton, Neptune's brightest satellite, can be located using the Sky & Telescope interactive observing tool at https://skyandtelesc...triton-tracker/
The dwarf planet Pluto is located near the Teaspoon asterism in northeastern Sagittarius at a declination of nearly -23.0 degrees. Finder charts can be found at pages 48 and 49 of the July 2021 issue of Sky & Telescope and on page 243 of the RASC Observer’s Handbook 2021.
For more on the planets and how to locate them, see http://www.nakedeyeplanets.com/
The Distance, Brightness, and Apparent Size of Planets graphic at https://www.timeandd...lanets/distance displays the apparent and comparative sizes of the planets, along with their magnitudes and distances, on a given date and time.
Comet C/2020 T2 (Palomar) is predicted to be the brightest comet visible this month. It heads to the southeast through Virgo and into Libra. The periodic comet 15P/Finlay passes northeastward through Taurus and into Gemini. Comet 67P/Churyumov-Gerasimenko is a rather faint target as it travels northeastward through Aries and Taurus. This periodic comet orbits the Sun once every 6.5 years between the orbits of Jupiter and Earth. It was visited by the Rosetta spacecraft and the Philae probe seven years ago. Visit http://cometchasing.skyhound.com/ and http://www.aerith.ne...t/future-n.html and https://cobs.si/ for additional information on comets visible this month.
Asteroid 89 Julia shines at ninth-magnitude as it heads northwestward through Aquarius. It passes several degrees north of the globular cluster M2 on September 24th and September 25th. Asteroid 2 Pallas reaches opposition in Pisces on September 11th. A finder chart can be found on page 49 of the September 2021 issue of Sky & Telescope. Other asteroids brighter than magnitude +11.0 reaching opposition this month include 532 Herculina on September 19th and 980 Anacostia on September 30th. On the morning of September 17th, the dwarf planet/asteroid 1 Ceres passes just four arc minutes south of the fifth-magnitude star Sigma1 Tauri. Data on asteroid occultations taking place this month is available at http://www.asteroido.../2021_09_si.htm and http://www.poyntsour.../New/Global.htm
An online data generator for various astronomical events is available at https://astronomynow.com/almanac/
The famous eclipsing variable star Algol (Beta Persei) is at a minimum, decreasing in brightness from magnitude +2.1 to magnitude +3.4, on September 1st, 4th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 27th, and 30th. Consult page 50 of the September 2021 issue of Sky & Telescope for the minima times. On the morning of September 8th, Algol shines at minimum brightness (magnitude +3.4) for approximately two hours centered at 2:55 a.m. EDT (6:55 UT). It does the same at 11:44 p.m. EDT (3:44 UT September 13th) on the night of September 12th. For more on Algol, see http://stars.astro.i.../sow/Algol.html and http://www.solstatio...ars2/algol3.htm
Weather and observing conditions forecasts are available at https://www.cleardar.../csk/index.html
Data on current supernovae can be found at http://www.rochester...y.org/snimages/
Telrad finder charts for the SAC’s 110 Best of the NGC are available at http://sao64.free.fr...ataloguesac.pdf
Information pertaining to observing some of the more prominent Messier galaxies can be found at http://www.cloudynig...ur-astronomers/
Author Phil Harrington offers an excellent freeware planetarium program for binocular observers known as TUBA (Touring the Universe through Binoculars Atlas), which also includes information on purchasing binoculars, at http://www.philharrington.net/tuba.htm
Deep-sky object list generators can be found at www.virtualcolony.com/sac/ and www.tonightssky.com/MainPage.php and https://telescopius....?fromdsobrowser
Eighty binary and multiple stars for September: 12 Aquarii, Struve 2809, Struve 2838 (Aquarius); Alpha Capricorni, Sigma Capricorni, Nu Capricorni, Beta Capricorni, Pi Capricorni, Rho Capricorni, Omicron Capricorni, h2973, h2975, Struve 2699, h2995, 24 Capricorni, Xi Capricorni, Epsilon Capricorni, 41 Capricorni, h3065 (Capricornus); Kappa Cephei, Struve 2751, Beta Cephei, Struve 2816, Struve 2819, Struve 2836, Otto Struve 451, Struve 2840, Struve 2873 (Cepheus); Otto Struve 394, 26 Cygni, h1470, h1471, Omicron Cygni, Struve 2657, 29 Cygni, 49 Cygni, 52 Cygni, 59 Cygni, 60 Cygni, 61 Cygni, Struve 2762 (Cygnus); Struve 2665, Struve 2673, Struve 2679, Kappa Delphini, Struve 2715, Struve 2718, Struve 2721, Struve 2722, Struve 2725 (in the same field as Gamma Delphini), Gamma Delphini, 13 Delphini, Struve 2730, 16 Delphini, Struve 2735, Struve 2736, Struve 2738 (Delphinus); 65 Draconis, Struve 2640 (Draco); Epsilon Equulei, Lambda Equulei, Struve 2765, Struve 2786, Struve 2793 (Equuleus); 1 Pegasi, Struve 2797, h1647, Struve 2804, Struve 3112, 3 Pegasi, 4 Pegasi, Kappa Pegasi, h947, Struve 2841, Struve 2848 (Pegasus); h1462, Struve 2653, Burnham 441, Struve 2655, Struve 2769 (Vulpecula)
Notable carbon star for September: LW Cygni
Fifty deep-sky objects for September: M2, M72, M73, NGC 7009 (Aquarius); M30, NGC 6903, NGC 6907 (Capricornus); B150, B169, B170, IC 1396, NGC 6939, NGC 6946, NGC 6951, NGC 7023, NGC 7160, NGC 7142 (Cepheus); B343, B361, Ba6, Be87, Cr 421, Do9, IC 4996, M29, M39, NGC 6866, NGC 6871, NGC 6888, NGC 6894, NGC 6910, NGC 6960, NGC 6992, NGC 6994, NGC 6995, NGC 7000, NGC 7008, NGC 7026, NGC 7027, NGC 7039, NGC 7048, NGC 7063, NGC 7086 (Cygnus); NGC 6891, NGC 6905, NGC 6934, NGC 7006 (Delphinus); NGC 7015 (Equuleus); M15 (Pegasus); NGC 6940 (Vulpecula)
Top ten binocular deep-sky objects for September: IC 1396, LDN 906, M2, M15, M29, M30, M39, NGC 6939, NGC 6871, NGC 7000
Top ten deep-sky objects for September: IC 1396, M2, M15, M30, NGC 6888, NGC 6946, NGC 6960, NGC 6992, NGC 7000, NGC 7009
Challenge deep-sky object for September: Abell 78 (Cygnus)
The objects listed above are located between 20:00 and 22:00 hours of right ascension.