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September 2012 Astronomical Calendar

Dave Mitsky

Note: All times in UTC (EST + 5)

Karl Harding discovered asteroid 3 Juno on September 1, 1804. E. E. Barnard discovered Jupiter's fifth satellite, fourteenth-magnitude Amalthea, using the 36-inch refractor at the Lick Observatory on September 9, 1892. On September 19, 1848, William Bond discovered Saturn's fourteenth-magnitude satellite Hyperion, the first irregular moon to be discovered. Neptune was discovered by Johann Gottfried Galle on September 23, 1846, using Urbain Le Verrier's calculations of its position.

The zodiacal light, or the false dawn, is visible about two hours before sunrise from a dark site during the latter part of September.

The Moon is 14.4 days old and is located in Pisces on September 1 at 0:00 UT. The Moon is at its greatest northern declination (+21.2 degrees) on September 8 and its greatest southern declination (-21.1 degrees) on September 22. Longitudinal libration is at a maximum of +5.6 degrees on September 27 and a minimum of -5.8 degrees on September 13. Latitudinal libration is at a maximum of +6.7 degrees on September 14 and a minimum of -6.7 degrees on September 27. Visit http://saberdoesthestars.wordpress.com/2011/07/05/saber-does-the-stars/ for tips on spotting extreme crescent Moons. Times and dates for the lunar light rays predicted to occur in June are available at http://www.lunar-occultations.com/rlo/rays/rays.htm

The Sun is located in Leo on September 1. It crosses the celestial equator from north to south on September 22, 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 1: Mercury (magnitude -1.4, 5.3", 93% illuminated, 1.27 a.u., Leo), Venus (magnitude -4.3, 19.9", 58% illuminated, 0.84 a.u., Gemini), Mars (magnitude 1.2, 5.2", 91% illuminated, 1.80 a.u., Virgo), Jupiter (magnitude -2.3, 39.2", 99% illuminated, 5.03 a.u., Taurus), Saturn (0.8 magnitude, 16.0", 100% illuminated, 10.42 a.u., Virgo), Uranus (5.7 magnitude, 3.7", 100% illuminated, 19.17 a.u., Cetus), Neptune (7.8 magnitude, 2.3", 100% illuminated, 28.99 a.u., Aquarius), and Pluto (14.1 magnitude, 0.1", 100% illuminated, 31.81 a.u., Sagittarius).

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

For observers at latitude 40 degrees north at midmonth, Venus rises at 3:00 a.m. local time, Mars sets at 9 p.m. local time, Jupiter rises at 11:00 p.m. local time, and transits the meridian at 6:00 a.m. local time, and Saturn sets at 9:00 p.m. local time.

During September, Mercury decreases both in brightness and in apparent size. It is potentially visible, under exceptional conditions, extremely close to the horizon during evening twilight at the very end of the month.

Venus shines brightly at minus fourth magnitude and, as September progresses, shrinks in apparent size from 20 to 16 arc seconds. It begins the month in Gemini, starts to traverse Cancer on September 4, and enters Leo on September 23. On the morning of September 12, Venus lies four degrees northeast of a waning crescent Moon and three degrees southwest of the naked-eye open cluster M44.

Mars departs Virgo and crosses into Libra on September 4. It passes one degree south of the third-magnitude multiple star Zubenelgenubi (Alpha Librae) on September 14 and is occulted by the Moon on September 19. Mars is only 4.8 arc seconds in apparent size by month's end.

Jupiter increases in apparent size by four arc seconds and brightens from magnitude -2.3 to magnitude -2.5 this month. A double Galilean satellite shadow transit takes place on September 1. Jupiter reaches western quadrature on September 7. The Last Quarter Moon passes very close to the giant planet on September 8. Click on http://www.skyandtelescope.com/observing/objects/planets/3304091.html?page=1&c=y to determine transit times of the central meridian by the Great Red Spot. Data on the Galilean satellites is available at http://www.skyandtelescope.com/observing/objects/javascript/3307071.html

Saturn disappears into the glare of the Sun this month. Mars and Saturn are ten degrees apart on September 1.

Uranus is located just to the southwest of 44 Piscium when it reaches opposition on the evening of September 29 and can be seen without optical aid from a dark site. At that time, Uranus is 0.3 degree north of the celestial equator and approximately 2.6 light hours or 1.77 billion miles from the Earth.

Neptune can be found approximately one degree east of the fifth-magnitude star 38 Aquarii on September 1. On September 30, it's 22 arc minutes southeast of that star.

Finder charts for Uranus and Neptune can be found at http://media.skyandtelescope.com/documents/Uranus-Neptune-2012.pdf and page 50 of the September issue of Sky & Telescope.

Pluto is located in northern Sagittarius near the open cluster M25. The dwarf planet culminates during the mid-evening. On September 30, Pluto lies about seven arc minutes from the orange-hued, eighth-magnitude star HD 170120. Detailed finder charts are available on pages 52 and 53 of the June issue of Sky & Telescope and on page 236 of the RASC Observer's Handbook 2012.

For more on the planets and how to locate them, see http://www.nakedeyeplanets.com/

Comet C/2011 F1 (LINEAR) heads southeastward through the constellation of Bootes. The tenth- to-eleventh magnitude comet is located due east of the fourth-magnitude star Zeta Bootis on the night of September 11. For additional information on comets visible in September, browse http://cometchasing.skyhound.com/ and http://www.aerith.net/comet/future-n.html

Asteroids 1 Ceres and 4 Vesta shine at ninth and eighth magnitude respectively as they pass through Taurus during September. A finder chart appears on page 53 of the August issue of Sky & Telescope. The eighth-magnitude asteroid 2 Pallas reaches opposition in Cetus at 11:00 p.m. EDT on September 24. Asteroid 11 Parthenope glows at ninth magnitude as it travels southwestward through Aquarius. It reaches opposition on the morning of September 3. The ninth-magnitude minor planet can be found less than one degree due north of the fourth-magnitude star Tau² Aquarii on the night of September 13. Asteroid 18 Melpomene travels through southwestern Serpens Cauda. The faint asteroid 363 Padua occults Zubenelgenubi during the daytime on September 16. See http://www.skyandtelescope.com/skytel/beyondthepage/Four-occultations-in-September-2012-158607465.html for further information. Data on asteroid occultations taking place this month is available at http://www.asteroidoccultation.com/2012_09_si.htm and http://www.poyntsource.com/New/Global.htm

A free star map for September can be downloaded at http://www.skymaps.com/downloads.html

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

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.