September 2010 Celestial Calendar & Observing Notes c/o Dave Mitsky

[Big Dipper]

September 2010 Celestial Calendar & Observing Notes courtesy of Dave Mitsky (calendar data also reproduced in our forum calendar).

All times, unless otherwise noted, are UT.

September 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 Moon is 0.8 degree south of the bright open cluster M45 (the Pleiades) in Taurus at 0:00; Last Quarter Moon occurs at 17:22; Venus is 1.2 degrees south of the first-magnitude star Spica (Alpha Virginis) at 18:00

9/2 The Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to occur at 6:45

9/3 The Moon is 0.2 degree south of the bright open cluster M35 in Gemini at 11:00; Mercury is in inferior conjunction at 13:00

9/4 Mars is 2 degrees north of Spica at 14:00

9/6 Venus is at aphelion today; Mars is at the descending node today

9/8 The Moon is at perigee, subtending 33'04" from a distance of 357,190 kilometers (221,948 miles), at 3:58; New Moon (lunation 1085) occurs at 10:30

9/9 Saturn is 8 degrees north of the Moon at 22:00

9/11 Asteroid 8 Flora (magnitude 8.2) is at opposition at 3:00; Venus is 0.3 degrees north of the Moon, with an occultation taking place in the South Indian Ocean, southwestern Africa, the southern Atlantic Ocean, and eastern Brazil, at 13:00

9/12 Mercury is stationary at 3:00

9/14 Pluto is stationary today; asteroid 39 Laetitia (magnitude 9.1) is at opposition at 10:00

9/15 First Quarter Moon occurs at 5:50; 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 15:07

9/16 Mercury is at the ascending node today

9/19 Mercury is at greatest western elongation (18 degrees) at 18:00

9/20 Neptune is 5 degrees south of the Moon at 16:00

9/21 Mercury is at perihelion today; asteroid 6 Hebe (magnitude 7.7) is at opposition at 6:00; the Moon is at apogee, subtending 29'29" from a distance of 406,165 kilometers (252,379 miles), at 8:02; Jupiter (apparent size 49.8", magnitude -2.9) is at opposition at 12:00; Uranus (apparent size 3.7", magnitude 5.7) is at opposition at 17:00

9/22 Jupiter is 0.9 degree south of Uranus at 19:00

9/23 The autumnal equinox occurs in the northern hemisphere at 3:09; Full Moon (known as the Barley, Corn, or Fruit Moon), this year’s Harvest Moon, occurs at 9:17; Jupiter is 7 degrees south of the Moon at 11:00; Uranus is 6 degrees south of the Moon at 11:00; Venus is at greatest brilliancy (magnitude -4.8) at 20:00

9/28 Venus is at its greatest heliocentric latitude south today; the Moon is 1.1 degrees south of M45 (the Pleiades) at 6:00

9/29 Venus is 6 degrees south of Mars at 6:00

9/30 The Moon is 0.5 degree south of M35 at 18:00

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

A normally minor meteor shower, the Alpha Aurigids (5 per hour), peaks on the morning of September 1. However, this shower produced an outburst of 130 meteors per hour in 2007.

The Moon is 21.9 days old and is located in Taurus on September 1 at 0:00 UT. The Moon occults Venus on September 11. Browse Web Page Redirection for IOTA for additional information on this occultation. The Moon is at its greatest northern declination on September 2 (24.7 degrees) and September 29 (24.5 degrees) and its greatest southern declination on September 15 (-24.7 degrees). Longitudinal libration is at a maximum of 8.0 degrees on September 14 and a minimum of -7.3 degrees on September 2 and -6.6 degrees on September 30. Latitudinal libration is at a maximum of 6.6 degrees on September 9 and a minimum of -6.5 degrees on September 24. Visit Extreme Lunar Crescent Data [L1085-90] | Saber Does The Stars for tips on spotting extreme crescent Moons. Times and dates for the lunar light rays predicted to occur this month are available at Lunar Sunrise/Sunset Crater Rays

The Sun is located in Leo on September 1. It crosses the celestial equator from north to south on September 23, 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 (4.6 magnitude, 10.7", 2% illuminated, 0.63 a.u., Sextans), Venus (-4.6 magnitude, 28.3", 42% illuminated, 0.59 a.u., Virgo), Mars (1.5 magnitude, 4.4", 95% illuminated, 2.15 a.u., Virgo), Jupiter (-2.9 magnitude, 49.1", 100% illuminated, 4.01 a.u., Pisces), Saturn (1.0 magnitude, 15.9", 100% illuminated, 10.45 a.u., Virgo), Uranus (5.7 magnitude, 3.7", 100% illuminated, 19.15 a.u., Pisces), Neptune (7.8 magnitude, 2.3", 100% illuminated, 29.03 a.u., Capricornus), and Pluto (14.1 magnitude, 0.1", 100% illuminated, 31.46 a.u., Sagittarius)

This month Venus is located in the southwest, Mars and Saturn in the west, and Jupiter and Uranus in the east during the evening. Jupiter and Uranus lie in the southeastern sky and Neptune is in the south at midnight. Mercury, Jupiter, and Uranus are in the east in the morning.

At midmonth, Mercury is visible during morning twilight, Venus sets at 9:00 p.m. EDT, Mars sets at 9:00 p.m. EDT, Jupiter and Uranus are visible for the entire night, and Saturn sets before 8:00 p.m. EDT for observers at latitude 40 degrees north.

Mercury is in inferior conjunction on September 3. It undergoes its best morning apparition of 2010 during the second half of September. From September 11 to September 16, Mercury increases in magnitude from 2.0 to 0.2, while growing in illumination and shrinking in apparent size. On September 13, it should be visible 5.5 degrees below the first-magnitude star Regulus. Mercury brightens to magnitude -0.4 on September 19, when it reaches greatest western elongation. By the end of the month, Mercury shines at magnitude -1.1 and has only half the apparent diameter that it had on September 1.

On the evening of September 1, the first-magnitude star Spica lies 1.3 degrees from Venus and 3.3 degrees from Mars. Venus shines some three hundred times brighter than Mars. This astronomical trio persists through September 3, after which the three bodies will no longer fit into a five degree circle. During September, Venus increases in apparent size but decreases in phase. Venus attains maximum brightness on September 23.

The gap between Mars and Venus increases from four to seven degrees during September. From September 4 to September 6, Mars and Spica are a bit more than two degrees apart. The Red Planet exits Virgo and enters Libra near the end of September. By month’s end, Mars subtends only 4.2 arc seconds.

Jupiter passes 1.7 degrees south of the point of the vernal equinox on September 14. Jupiter and Uranus are closest to the Earth on September 20. (Jupiter is nearer to the Earth on September 20 than any time between 1963 and 2022.) The two planets reach opposition within five hours of each other on September 21, when Jupiter and Uranus will be located two degrees and one degree south of the celestial equator respectively. Jupiter will be almost 3,000 times brighter than Uranus. At local midnight, the two gas giants lie more than halfway to the zenith. Callisto undergoes its last shadow transit and last eclipse until 2013 on September 15 and September 23 respectively. When Jupiter is at opposition on September 21, Io and its shadow transit the planet simultaneously starting at 4:42 a.m. EDT. The four Galilean satellites all lie to the east of Jupiter on the morning of September 24. Io is closest, followed by Europa, Callisto, and Ganymede. E. E. Barnard discovered Jupiter’s fifth satellite, fourteenth-magnitude Amalthea, using the 36-inch refractor at the Lick Observatory on September 9, 1892. Browse SkyandTelescope.com - Planets - Transit Times of Jupiter's Great Red Spot to determine transits of the central meridian by the Great Red Spot. Data on the Galilean satellites is available at SkyandTelescope.com - Interactive Observing Tools - Jupiter's Moons Javascript Utility

Saturn sets one hour after the sun on September 1. The Ringed Planet crosses south of the celestial equator on September 8. It will remain there for the next 15 years. Saturn’s fourteenth-magnitude satellite Hyperion was discovered by William Bond on September 19, 1848.

Uranus shines at magnitude 5.7 when it reaches opposition on September 21and can be seen without optical aid from a dark site. Jupiter and Uranus are less than 1.5 degrees apart for most of the month. On September 18, the two gas giants are separated by only 0.8 degree.

Neptune is situated 0.7 degree northeast of the fifth-magnitude star Mu Capricorni and 3.5 degrees northeast of the third-magnitude star Delta Capricorni at mid-month. The eighth planet was discovered by Johann Gottfried Galle on September 23, 1846, using Urbain Le Verrier’s calculations of its position.

Finder charts for Uranus and Neptune are posted at http://media.skyandtelescope.com/documents/Uranus_Neptune_2010.pdf

Pluto lies near an eighth-magnitude star that’s located 2.6 degrees north of the fourth-magnitude star Mu Sagittarii. The dwarf planet culminates just after nightfall. A finder chart is available on page 60 of the July 2010 issue of Sky & Telescope and online at SkyandTelescope.com - SkyTel Beyond the Page - See Pluto in 2010

During September, the periodic comet 103P/Hartley glides northeastward through Cassiopeia. The short-period comet may brighten to tenth-magnitude by late September. Comet 103P/Hartley passes just north of R Cassiopeiae on September 24 and very close to Lambda Cassiopeia on September 29. Comet 10P/Tempel is also in Cetus. Another possible cometary target is Comet C/2009 K5 (McNaught). Browse Visual Comets in the Future (Northern Hemisphere) for additional information on these and other comets.

Asteroid 6 Hebe passes southwestward through Cetus this month. This Main Belt asteroid, which was discovered in 1847 by the amateur astronomer Karl Hencke, is positioned several degrees to the west of Beta Ceti on September 17. Hebe shines at magnitude 7.7 when it reaches opposition on September 21, the same day that Jupiter and Uranus are at opposition. Asteroids 8 Flora and 39 Laetitia also reach opposition this month. Karl Harding discovered asteroid 3 Juno on September 1, 1804. Information on asteroid occultations of stars can be found at Global Asteroid Events

A free star map for September can be downloaded at Skymaps.com - Publication Quality Sky Maps & Star Charts