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HomeMitsky's Celestial Calendar

Dave Mitsky's Celestial Calendar for September 2018

All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)


9/1   The equation of time equals 0 at 14:00

9/2   Venus is 1.4 degrees south of the first-magnitude star Spica (Alpha Virginis) at 9:00; the Moon is 8.8 degrees south-southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 9:00; Mercury is at perihelion (0.30749 astronomical units from the Sun) at 10:00; asteroid 115 Thyra (magnitude +9.9) is at opposition in Pegasus at 12:29

9/3   The Moon is 1.2 degrees north-northwest of the first-magnitude star Aldebaran (Alpha Tauri), with an occultation taking place in far northern Canada and Greenland, at 2:00; Last Quarter Moon occurs at 2:37; a double Galilean satellite shadow transit begins at 18:31; the Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to be visible at 18:52

9/5   Venus is at aphelion (0.72824 astronomical units from the Sun) at 8:00; Mercury is 1.0 degree north of the first-magnitude star Regulus (Alpha Leonis) at 23:00; asteroid 27 Euterpe (magnitude +9.8) is at opposition in Aquarius at 23:39

9/6   The Moon is 7.3 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 4:00; Saturn is stationary in right ascension at 9:00; Saturn is stationary in longitude at 10:00; the Moon is at the ascending node (longitude 125.4 degrees) at 22:43

9/7   The Moon is 1.4 degrees south of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 3:00; a double Galilean satellite shadow transit begins at 7:50; Neptune (magnitude +7.8, apparent size 2.4") is at opposition at 18:00

9/8   The Moon is at perigee, subtending 33' 04" from a distance of 361,351 kilometers (224,533 miles), at 1:20; the Moon  is 1.7 degrees north-northeast of Regulus at 14:00; the Moon is 0.89 degree north-northeast of Mercury at 23:00

9/9   New Moon (lunation 1184) occurs at 18:01

9/10 Comet 21P/Giacobini-Zinner is at perihelion (1.013 astronomical units from the Sun) at 7:46

9/12 The Moon is 7.1 degrees north-northeast of Spica at 8:00; Mercury is at its greatest heliocentric latitude north (7.0 degrees north of the ecliptic plane) at 15:00; the Moon is 9.9 degrees north-northeast of Venus at 22:00

9/14 The Moon is 4.2 degrees north-northeast of Jupiter at 5:00

9/15 The Moon is 8.8 degrees north of Antares at 21:00

9/16 Mars (magnitude -1.7) is at perihelion (1.38144 astronomical units from the Sun) at 13:00; First Quarter Moon occurs at 23:15

9/17 Sunrise takes place at the isolated lunar mountain Mons Pico at 9:24; the Moon is 2.1 degrees north of Saturn at 17:00

9/18 Sunrise takes place at the isolated lunar mountain Mons Piton at 00:19; asteroid 173 Ino (magnitude +10.3) is at opposition in Cetus at 1:56; the Lunar X (the Purbach or Werner Cross), an X-shaped illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to occur at 6:26

9/19 Asteroid 30 Urania (magnitude +9.6) is at opposition in Pisces at 1:57

9/20 The Moon is at apogee, subtending 29' 31" from a distance of 404,876 kilometers (251,578 miles), at 0:53; the Moon is 4.7 degrees north of Mars at 7:00

9/21 Mercury is in superior conjunction with the sun (1.387 astronomical units from the Earth) at 2:00; Venus is at its greatest illuminated extent at 10:00

9/23 The autumnal equinox occurs in the northern hemisphere at 1:54; the Moon is 2.3 degrees south-southeast of Neptune at 17:00

9/24 Asteroid 10 Hygiea (magnitude +10.1) is at opposition in Pisces at 0:44

9/25 Full Moon (known as the Barley, Corn, or Fruit Moon), this year’s Harvest Moon, occurs at 2:52

9/27 Asteroid 4 Vesta (magnitude +7.4) is 2.8 degrees south of Saturn (magnitude +0.6) at 9:20; the Moon is 4.5 degrees south-southeast of Uranus at 10:00; Venus is at its greatest heliocentric latitude south (3.4 degrees south of the ecliptic plane) at 13:00

9/29 Venus is 13.8 degrees west-southwest of Jupiter at 0:00; the Moon is 8.6 degrees south-southeast of M45 at 14:00

9/30 Pluto is stationary in right ascension at 5:00; the Moon is 1.4 degrees north of Aldebaran at 8:00; Mars and Neptune are at heliocentric conjunction (heliocentric longitude 345.6 degrees) at 8:00; Pluto is stationary in longitude at 17:00


Nicolas Louis de Lacaille and Johann Gottfried Galle were born this month.

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.

The minor meteor shower known as the Aurigids, which has a maximum hourly rate of just six per hour, peaks on the evening of September 1st. A waxing gibbous Moon sets before the radiant is high in the sky. The peak of the minor meteor shower known as the Epsilon Perseids, with a maximum hourly rate of just five per hour, takes place on the evening of September 9th, the night of the New Moon. The radiant is located near the second-magnitude star Algol (Beta Persei) at 03h15m, +40 degrees.

The Moon is 19.4 days old, subtends 30.5 arc minutes, is illuminated 82.3%, and is located in Pisces on September 1st at 0:00 UT. The Moon is at its greatest northern declination (+20.7 degrees) on September 5th and its greatest southern declination (-20.8 degrees) on September 18th. Longitudinal libration is at a maximum of +7.0 degrees on September 14th and a minimum of -6.2 degrees on September 1st. Latitudinal libration is at a maximum of +6.7 degrees on September 11th and +6.6 degrees on September 28th and a minimum of -6.7 degrees on September 13th. An article on lunar libration appears on pages 52-54 of the September 2018 issue of Sky & Telescope. New Moon occurs on September 9th. The Moon is at perigee (56.65 Earth-radii distant) on September 8th and at apogee (63.48 Earth-radii distant) on September 20th. The waning gibbous Moon occults Aldebaran, the brightest star that it ever can occult, from certain parts of the world on September 3rd. Consult for further information on this event Visit tips on spotting extreme crescent Moons and for Full Moon data. Times and dates for the lunar light rays predicted to occur in June are available at


Information on passes of the ISS, the Tiangong-2, the USAF’s X-37B, the HST, and other satellites can be found at


The zodiacal light, or the false dawn, is visible about two hours before sunrise from a dark site during the middle part of September. Articles on the zodiacal light appear at and


The Sun is located in Leo on September 1st. The Sun crosses the celestial equator from north to south at 1:54 UT on September 23rd, 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 -0.8, 6.4", 65% illuminated, 1.06 a.u., Leo), Venus (magnitude -4.6, 29.1", 40% illuminated, 0.57 a.u., Virgo), Mars (magnitude -2.1, 20.9", 94% illuminated, 0.45 a.u., Sagittarius), Jupiter (magnitude -1.9, 34.8", 99% illuminated, 5.67 a.u., Libra), Saturn (magnitude +0.4, 17.3", 100% illuminated, 9.61 a.u., Sagittarius), Uranus (magnitude +5.7, 3.7", 100% illuminated, 19.08 a.u. on September 16th, Aries), Neptune (magnitude +7.8, 2.4", 100% illuminated, 28.95 a.u. on September 16th, Aquarius), and Pluto (magnitude +14.2, 0.1", 100% illuminated, 33.18 a.u. on September 16th, Sagittarius).


This month Venus and Jupiter are located in the southwest, Mars and Saturn in the south, and Neptune in the east during the evening. At midnight, Mars and Saturn can be found in the southwest, Uranus in the east, and Neptune in the south. Mercury is in the east, Uranus is in the southwest, and Neptune is in the west in the morning sky.


Mercury attains an altitude of ten degrees in the east-northeast 30 minutes before sunrise on September 1st. It is at perihelion on September 2nd. On the morning of September 5th, Mercury is 1.5 degrees north of Regulus. The speediest planet is lost in the Sun’s glare by September 11th. On September 12th, it’s at its greatest heliocentric latitude south. Mercury is in superior conjunction with the Sun on September 21st.


During September, Venus increases in apparent size from 29.1 to 45.5 arc seconds while decreasing in illumination from 40 to 18%. It reaches a peak brightness of magnitude -4.8. Venus passes 1.4 degrees south of Spica on September 2nd and is at aphelion on September 5th. A slender crescent Moon passes ten degrees north of Venus on September 12th. The brightest planet reaches its greatest illuminated extent on September 21st when it is at a declination of -19 degrees and is at its greatest latitude south of the ecliptic plane on September 27th. On the evenings of September 27th through September 29th, Venus and Jupiter are separated by less than fourteen degrees. The altitude of Venus at sunset decreases from approximately fifteen degrees to seven degrees this month for observers at latitude 40 degrees north.


Mars decreases in apparent magnitude from -2.1, which is brighter than Jupiter, to -1.3 as it travels eastward through western Capricornus this month. Its apparent diameter shrinks from 20.9 to 16.0 arc seconds. Mars crosses the meridian at approximately 10:20 p.m. local time on the first day of September and shortly before 9:00 p.m. local time on the last day of the month. It sets just before 3:00 a.m. local time on September 1st and just after 1:30 a.m. local time on September 30th. The Red Planet is at perihelion on September 16th. In North America, the gibbous Moon passes five degrees north of Mars on the evening of September 19th/20th. Martian surface feature simulators are available at and


Jupiter sets around 10:15 p.m. EDT in early September. At that time, it lies a bit more than two degrees from Zubenelgenubi (Alpha Librae). The waxing crescent Moon passes four degrees to the north of the planet on the evening of September 13th. Jupiter decreases in brightness by 0.1 magnitude and 2.1 arc seconds in angular diameter this month. Browse and to determine transit times of Jupiter’s central meridian by the Great Red Spot. That information also appears on page 51 of the September 2018 issue of Sky & Telescope. Data on the Galilean satellites is available online at and and on page 51 of the September 2018 issue of Sky & Telescope


Saturn culminates an hour after sunset on the first day of September and sets before midnight local daylight time by the end of the month. Its rings span 38 arc seconds and are tilted 27 degrees with respect to the Earth, the maximum tilt of 2018. On September 1st, Saturn is situated 1.7 degrees to the east of M20 (the Lagoon Nebula) and 2.2 degrees to the northeast of M8 (the Lagoon Nebula). Saturn reaches its second stationary point on September 6th and resumes direct or prograde (eastward) motion. By the end of September, Saturn’s eastward motion takes it 2.2 degrees to the east of M20. The Ringed Planet is two degrees south of the waxing gibbous Moon on September 17th. Saturn is at eastern quadrature on September 26th. Saturn’s odd satellite Iapetus shines at tenth magnitude on September 1st, when it is located 8.4 arc minutes to the west of the planet. Iapetus dims to eleventh magnitude as it passes 1.7 arc minutes to the north of Saturn on September 18th. Twelfth-magnitude Enceladus and thirteenth-magnitude Mimas both reach greatest eastern elongation on the night of September 20/September 21st. An illustration showing their positions can be seen on page 42 of the September 2018 issue of Astronomy. For further information on Saturn’s satellites, browse 


Uranus is located in southwestern Aries, twelve degrees south of the second-magnitude star Hamal (Alpha Arietis). The waning gibbous Moon passes five degrees south of the planet on September 7th. Browse for a finder chart.  


Neptune is located 2.2 degrees west-southwest of the fourth-magnitude star Phi Aquarii on the first day of September. The ice giant planet subtends just 2.4 arc seconds, shines at magnitude +7.8, and lies at a distance of 4.0 light hours when it reaches opposition on September 7th. A finder chart for that night appears on page 36 of the September 2018 issue of Astronomy. The waning gibbous Moon passes two degrees to the south of Neptune on September 27th. A finder chart is posted  


Additional online finder charts for Uranus and Neptune can be found at and and also at  and on pages 48 and 49 of the September 2018 issue of Sky & Telescope.


Pluto is located below the Teaspoon asterism in northeastern Sagittarius at a declination of nearly -22 degrees. The dwarf planet is highest in altitude in the late evening. Finder charts for Pluto are available on pages 48 and 49 of the July 2018 issue of Sky & Telescope and page 243 of the RASC Observer’s Handbook 2018. A finder chart is posted online at


For more on the planets and how to locate them, see


Comet 21P/Giacobini-Zinner, which is the source of October's Draconid or Giacobinid meteor shower, travels southeastward through Auriga, Taurus, and Gemini in September. Reaching a predicted peak brightness of magnitude seven in September, this comet is a fine binocular object. It passes within two degrees of the first-magnitude star Capella (Alpha Aurigae) on September 2nd and September 3rd and within two degrees to the east of the open clusters M36 and M38 on September 7th and September 8th. The periodic comet can be found approximately one degree from the rich open cluster M37 on September 10th. Comet 21P reaches perihelion (1.013 astronomical units from the Sun) on September 10th. It passes closest to the Earth (0.392 astronomical units distant) on September 11th and briefly enters Taurus on September 13th. On September 14th, the comet enters Gemini. It passes by the bright open cluster M35 on September 15th and very near the third-magnitude star Propus (Eta Geminorum) on September 16th. Comet 21P crosses into Orion on September 17th, reenters Gemini on September 21st, and enters Monoceros on September 23rd. It passes near NGC 2264 (the Christmas Tree Cluster) on September 24th, within on half of a degree of the open cluster NGC 2254 on September 26th, and less than two degrees from NGC 2237 (the Rosette Nebula) on the morning of September 27th. Additional information can be found at and and on page 50 of the August 2018 issue of Sky & Telescope. For further information on comets visible this month, browse and 


Asteroid 4 Vesta shines at seventh magnitude as it heads mostly eastward through Sagittarius this month.  The main belt asteroid passes about one degree south of M8 (the Lagoon Nebula) on the nights of September 20th and September 21st. On the nights of September 23rd and September 24th, Vesta glides between the eighth-magnitude globular clusters NGC 6544 and NGC 6553. The following asteroids brighter than 11th magnitude are at opposition this month: asteroid 115 Thyra (magnitude +9.9) on September 2nd, asteroid 27 Euterpe (magnitude +9.8) on September 5, asteroid 173 Ino (magnitude +10.3) on September 18th, asteroid 30 Urania (magnitude +9.6) on September 19th, and asteroid 10 Hygiea (magnitude +10.1) on September 24th. The S-type main belt asteroid 80 Sappho (magnitude +11.8) occults the A2-type star HD 33864 (HIP 244403) on the morning of September 16th. Data on this and other asteroid occultations taking place this month is available at and

Free star maps for this month can be downloaded at and


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 2nd, 5th, 8th, 10th, 13th, 16th, 19th, 22nd, 25th, and 28th. Consult page 50 of the September 2018 issue of Sky & Telescope for the minima times. On the night of September 7th, Algol shines at minimum brightness (magnitude +3.4) for approximately two hours on centered at 10:29 p.m. EDT (2:29 UT on September 8th). It does the same at 0:09 a.m. EDT (4:09 UT) on the morning of September 28th.  For more on Algol, see and 


A wealth of current information on solar system celestial bodies is posted at and


Various events taking place within our solar system are discussed at


Information on the celestial events transpiring each week can be found at and


Free star charts for the month can be downloaded at and


Data on current supernovae can be found at


Finder charts for the Messier objects and other deep-sky objects are posted at and and


Telrad finder charts for the Messier Catalog and the SAC’s 110 Best of the NGC are posted at and respectively.


Information pertaining to observing some of the more prominent Messier galaxies can be found at


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


Stellarium and Cartes du Ciel are useful freeware planetarium programs that are available at and


Deep-sky object list generators can be found at and and


Freeware sky atlases can be downloaded at and


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


Forty-five 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 4343, B361, Ba6, Be87, Cr 421, Do9, IC 1369, IC 4996, IC 1516, LDN 906, M29, M39, NGC 6866, NGC 6871, NGC 6888, NGC 6894, NGC 6910, NGC 6960, NGC 6992, NGC 7000, NGC 7008, NGC 7026, NGC 7027, NGC 7039, 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.