September 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 2:00
9/2 Full Moon (known as the Barley, Corn, or Fruit Moon) occurs at 5:22; asteroid 2 Pallas is stationary at 13:00
9/3 The Moon is 3.9 degrees southeast of Neptune at 1:00
9/4 The Martian winter solstice occurs at 4:00
9/6 The Moon is 0.03 degrees north of Mars, with an occultation occurring in southern Europe, northern Africa, Cape Verde Island, and central and northeastern South America, at 5:00; the Moon is at apogee, subtending 29' 28" from a distance of 405,607 kilometers (252,032 miles), at 6:29
9/7 The Moon is 3.0 degrees south of Uranus at 4:00
9/8 Mercury is at the descending node through the ecliptic plane at 18:00
9/9 The Moon is 6.2 degrees southeast of the bright open cluster M45 (the Pleiades or Subaru) in the constellation of Taurus at 0:00; the Moon is 4.1 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 18:00; Mars is stationary at 18:00
9/10 Last Quarter Moon occurs at 9:26; the Moon is at the ascending node (longitude 85.2 degrees) at 23:00
9/11 The Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to be visible at 00:32; asteroid 19 Fortuna (magnitude +9.4) is at opposition in the constellation of Pisces at 7:00; the Moon is 0.3 degrees south of the bright open cluster M35 in the constellation of Gemini at 13:00; Neptune (magnitude +7.8, angular size 2.3") is at opposition at 20:00
9/13 Jupiter is stationary, with prograde (direct or eastward) motion to resume at 0:00; the Moon is 7.9 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 0:00; the Moon is 4.3 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 5:00; Venus is 2.3 degrees south of the bright open cluster M44 (the Beehive Cluster or Praesepe) in the constellation of Cancer at 10:00
9/14 The Moon is 2.1 degrees north-northeast of M44 at 5:00; the Moon, Venus, and M44 lie within a circle with a diameter of 4.4 degrees at 6:00; a double Galilean satellite shadow transit (Callisto's shadow follows Io's) begins at 6:57; the Moon is 4.4 degrees north-northeast of Venus at 7:00; Jupiter is at its southernmost declination at 20:00
9/15 The Moon is 4.1 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 19:00
9/16 The Sun enters the constellation of Virgo, at longitude 174.2 degrees on the ecliptic, at 14:00
9/17 New Moon (lunation 1209) occurs at 11:00
9/18 The Moon is at perigee, subtending 33' 17" from a distance of 359,082 kilometers (223,123 miles), at 13:48
9/19 The Moon is 5.9 degrees north-northeast of Mercury at 3:00; Mercury is at aphelion (0.4667 astronomical units from the Sun) at 3:00; the Moon 6.4 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 10:00
9/22 Mercury is 0.3 degrees northeast of Spica at 12:00; the Sun's longitude is 180 degrees at 13:31; the northern hemisphere autumnal equinox occurs at 13:31; the Moon is 5.8 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 14:00
9/23 The Moon is at the descending node (longitude 263.9 degrees) at 13:00
9/24 First Quarter Moon occurs at 1:55; 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 fully formed at 13:09
9/25 The Moon is 1.6 degrees south of Jupiter at 7:00; the Moon is 2.3 degrees south of Saturn at 22:00
9/26 Venus at ascending node through the ecliptic plane at 22:00
9/29 Saturn is stationary, with prograde (direct or eastward) motion to resume, at 3:00
9/30 Asteroid 68 Leto (magnitude +9.6) is at opposition in the constellation of Cetus at 3:00; the Moon is 3.9 degrees southeast of Neptune at 6:00
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.
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 12.7 days old, subtends 30.4 arc minutes, is illuminated 98.1%, and is located in Capricornus on September 1st at 0:00 UT. The Moon is at its greatest northern declination (+24.3 degrees) on September 12th and its greatest southern declination (-24.4 degrees) on September 25th. Longitudinal libration is at a maximum of +7.1 degrees on September 25th and a minimum of -7.2 degrees on September 13th. Latitudinal libration is at a maximum of +6.5 degrees on September 3rd and a minimum of -6.5 degrees on September 17th. Favorable librations for the following lunar features occur on the indicated dates: Crater Compton on September 1st, Vallis Bouvard on September 14th, Crater Oken on September 21st, and Crater Humboldt on September 22nd. Parts of the eastern limb like Mare Marginis and the craters Goddard and Neper will be visible due to a favorable libration beginning on September 19th. New Moon occurs on September 17th. Large tides will occur for several days thereafter. The Moon is at apogee (63.59 Earth-radii distant) on September 6th and at perigee (56.30 Earth-radii distant) on September 18th. The Moon occults Mars on September 6th from certain parts of the world. Browse http://www.lunar-occ...ota/iotandx.htm for information on this event and other upcoming lunar occultations. Visit https://saberdoesthe...does-the-stars/ for tips on spotting extreme crescent Moons and http://www.curtrenz.com/moon06.html for Full Moon data. Consult http://time.unitariu...moon/where.html or download http://www.ap-i.net/avl/en/start for current information on the Moon. Visit https://www.fourmila...odMJtNWK1OLMxYk for a list of lunar maria and https://upload.wikim...tCZImsof8HUNAKI for a simple map of the Moon showing the most prominent maria. See https://svs.gsfc.nasa.gov/4768 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.../2020/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 15th. 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 13:31 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 -0.6, 5.0", 92% illuminated, 1.34 a.u., Leo), Venus (magnitude -4.3., 19.5", 60% illuminated, 0.86 a.u., Gemini), Mars (magnitude -1.8, 18.9", 92% illuminated, 0.50 a.u., Pisces), Jupiter (magnitude -2.6, 44.3", 99% illuminated, 4.45 a.u., Sagittarius), Saturn (magnitude +0.3, 18.0", 100% illuminated, 9.24 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, 28.93 a.u. on September 16th, Aquarius), and Pluto (magnitude +14.3, 0.1", 100% illuminated, 33.40 a.u. on September 16th, Sagittarius).
During the month of September, Mercury is located in the west, Jupiter and Saturn in the south, and Neptune in the east during the evening. At midnight, Mars and Uranus can be found in the east, Jupiter and Saturn in the southwest, and Neptune in the south. Venus is in the east, Mars and Uranus in the southwest, and Neptune is in the west in the morning sky.
This month, for the first time in decades, four planets (Venus, Mars, Jupiter, and Saturn) are all nearly at their best.
Mercury lies low in the west and sets less than 50 minutes after sunset as the month ends. The waxing crescent Moon passes six degrees north of Mercury on September 19th. Mercury passes within 0.7 degrees of Spica on September 21st. The two very different celestial objects are only five degrees in altitude 20 minutes after the Sun sets.
During September, Venus attains an altitude of almost 40 degrees in the mid-northern latitudes. It rises at approximately 3:00 a.m. local daylight-saving time on September 1st. The brightest planet is located in Gemini as September begins, crosses through Cancer, and ends the month in Leo. Venus decreases in brightness from magnitude -4.3 to magnitude -4.1, decreases in apparent size from 19.5 arc second to 15.6 arc seconds, and increases in illumination from 60% to 71%. At the time that the waning crescent Moon passes four degrees north of Venus on the morning of September 14th, the planet lies 2.5 degrees south of the large open cluster M44 in Cancer.
Mars rises about two hours after sunset as September begins and culminates around 4:00 a.m. local daylight-saving time. It brightens from magnitude -1.8 to magnitude -2.5, making it a bit brighter than Jupiter, and increases in angular size from 18.9 arc seconds to 22.4 arc seconds this month. Mars attains a maximum altitude of almost 60 degrees from mid-northern latitudes in the United States. The waning gibbous Moon passes very close to the Red Planet on the morning of September 6th, with an occultation taking place in certain parts of the world. Mars reaches its first stationary point approximately five degrees north of the fourth-magnitude star Alrescha (Alpha Piscium) on September 9th and then begins a retrograde loop. Prominent Martian surface features visible at 2:00 a.m. local daylight-saving time include Syrtis Major and the Hellas basin in early September, Mare Sirenum and Mare Cimmerium during the second week of the month, the Tharsis Ridge and Olympus Mons at mid-month, Vallis Marineris during the third week in September, and Sinus Sabaeus and Sinus Meridiani at the end of the month. Click on https://www.skyandte...watching-tools/ and https://www.calsky.c...gi/Planets/5/1? in order to determine what Martian surface features are visible.
Jupiter decreases in brightness to magnitude -2.4 and shrinks in angular diameter by 3.6 arc seconds this month. The gas giant reaches its second stationary point on September 13th. It then resumes prograde or eastward motion. The gap between Jupiter and Saturn that has grown by three degrees since May begins to close by month's end as Saturn also resumes eastward motion. The waxing gibbous Moon passes less than two degrees south of the Jupiter on September 25th. A double Galilean satellite shadow transit takes place on the morning of September 14th. Information on Great Red Spot transit times and Galilean satellite events is available on pages 50 and 51 of the September 2020 issue of Sky & Telescope and online at http://www.skyandtel...watching-tools/ and https://www.projectp...jevent.htm
During September, Saturn fades from magnitude +0.3 to magnitude +0.5 and shrinks in apparent size from 18.0 arc seconds to 17.2 arc seconds. Saturn’s rings span 40 arc seconds and are tilted 23 degrees with respect to the Earth. The waxing gibbous Moon passes two degrees south of the Ringed Planet on September 25th. Saturn reaches its second stationary point on September 29th and subsequently begins prograde or eastward motion. Eighth-magnitude Titan, Saturn’s largest and brightest satellite, is due north of the planet on September 1st and September 17th and due south of it on September 9th and September 25th. Saturn’s peculiar satellite Iapetus shines at almost eleventh magnitude on September 7th, when it is passes 63 arc seconds due north of the planet. For further information on Saturn’s satellites, browse http://www.skyandtel...tching-tools/
Uranus is located in southwestern Aries, eleven degrees south of the second-magnitude star Hamal (Alpha Arietis). The planet is located 0.6 degrees southwest of the sixth-magnitude star 19 Arietis on September 1st. By the end of the month, Uranus is more than one degree from the star. The waning gibbous Moon passes three degrees south of Uranus on the morning of September 7th. 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 can be found 2.5 degrees east of the fourth-magnitude star Phi Aquarii on the first day of September. The planet lies 1.5 degrees east of the star on September 30th. Neptune subtends 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 11th. The Full Moon passes four degrees south of Neptune on September 1st. The waxing gibbous Moon passes four degrees south of the planet on the night of September 29th. Browse http://www.nakedeyep...com/neptune.htm for a finder chart. An article on Neptune complete with finder charts appears on page 48 of the September 2020 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 in the vicinity of the Teaspoon asterism in northeastern Sagittarius at a declination of more than -22.5 degrees. Finder charts can be found at pages 48 and 49 of the July 2020 issue of Sky & Telescope and on page 243 of the RASC Observer’s Handbook 2020.
For more on the planets and how to locate them, see htp://www.nakedeyeplanets.com/
The Distance, Brightness, and Apparent Size of Planets graphic (Home / Sun & Moon / Planets / Distance, Brightness, and Apparent Size of Planets) 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.
During September, Comet 88P/Howell travels southeastward through Libra and Scorpius. It is at perihelion on September 26th and may reaches a maximum brightness of approximately ninth magnitude. On September 4th, the periodic comet passes 14 arc minutes southwest of the eighth-magnitude globular NGC 5897 in Libra. It glides between the globular clusters M80 and M4 in Scorpius on the evenings of September 22th through September 25th. Comet Howell passes approximately one degree north of Antares on the evenings of September 26th and September 27th. Consult page 49 of the September 2020 issue of Sky & Telescope for a finder chart. Browse http://cometchasing.skyhound.com/ and http://www.aerith.ne...t/future-n.html for further information on comets visible this month. Other sources of information include https://theskylive.com/comets and http://www.shopplaza...mets/comets.htm and http://britastro.org...arts_comet.html
The dwarf planet/asteroid 1 Ceres shines at magnitude +7.7 as it heads southwestward between Aquarius and Piscis Austrinus this month. Asteroids brighter than magnitude +11.0 reaching opposition this month include 17 Thetis (magnitude +10.7) on September 9th, 22 Kalliope (magnitude +10.6) on September 10th, 19 Fortuna (magnitude +9.4) on September 11th, and 68 Leto (magnitude +9.6) on September 30th. Data on asteroid occultations taking place this month is available at http://www.asteroido.../2020_09_si.htm and http://www.poyntsour.../New/Global.htm
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, 11th, 14th, 16th, 19th, 22nd, 25th, and 28th. Consult page 50 of the September 2020 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 2:30 a.m. EDT (6:30 UT). It does the same at 11:19 p.m. EDT (3:19 UT September 11th) on the night of September 10th. For more on Algol, see http://stars.astro.i.../sow/Algol.html and http://www.solstatio...2/algol3.htm
Data on current supernovae can be found at http://www.rochester...y.org/snimages/
Telrad finder charts for the Messier Catalog are posted at http://www.custerobs...cs/messier2.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
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.