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May 2012 Astronomical Calendar

Dave Mitsky

Note: All times in UTC (EST + 5)

Nicolas Lacaille (1713-1762) and Joseph Lockyer (1836-1920) were born this month.

The peak of the Eta Aquarid meteor shower is severely compromised by moonlight this year. Eta Aquarid meteors are debris from the famous periodic comet 1P/Halley.

The Moon is located in Sextans and is 9.7 days old on May 1 at 0:00 UT. The Moon is at its greatest northern declination on May 22 (+21.7 degrees) and its greatest southern declination on May 8 (-21.7 degrees). Longitudinal libration is at maximum (+7.5 degrees) on May 12 and at minimum (-7.4 degrees) on May 27. Latitudinal libration is at maximum (+6.8 degrees) on May 1 and (+6.9 degrees) on May 28 and at minimum (-6.8 degrees) on May 13. The largest Full Moon of 2012 occurs on May 6. Large tides will take place from May 6 through May 9. A difficult-to-observe occultation of the third-magnitude star Zeta Tauri by a very young Moon takes place in much of the western United States on May 22. See http://www.lunar-occultations.com/iota/iotandx.htm for additional information on lunar occultations. 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 this month are available at http://www.lunar-occultations.com/rlo/rays/rays.htm

The Sun is located in Aries on May 1. The first solar eclipse of 2012 takes place on May 20. An annular solar eclipse, the fifty-eighth eclipse of Saros 128, can be seen from eastern Asia, the northern Pacific, and the western United States and a partial eclipse from most of Asia, the Pacific, and the western two-thirds of North America. Greatest eclipse occurs at 23:52:47 UT, at which time the duration of annularity will be five minutes and forth-six seconds. For further information on this event, consult http://eclipse.gsfc.nasa.gov/SEmono/ASE2012/ASE2012.html and pages 50 and 51 of the May issue of Sky & Telescope.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on May 1: Mercury (magnitude -0.1, 6.4", 64% illuminated, 1.04 a.u., Pisces), Venus (magnitude -4.7, 37.4", 27% illuminated, 0.45 a.u., Taurus), Mars (magnitude 0.0, 9.9", 91% illuminated, 0.94 a.u., Leo), Jupiter (magnitude -2.0, 32.9", 100% illuminated, 5.99 a.u., Aries), Saturn (magnitude 0.3, 19.0", 100% illuminated, 8.76 a.u., Virgo), Uranus (magnitude 5.9, 3.4", 100% illuminated, 20.89 a.u., Pisces), Neptune (magnitude 7.9, 2.3", 100% illuminated, 30.36 a.u., Aquarius), and Pluto (magnitude 14.0, 0.1", 100% illuminated, 31.68 a.u., Sagittarius).

In the evening, Venus is the northwest, Mars is the southwest, and Saturn is in the southeast. Mars is in the west and Saturn in the south at midnight. Mercury and Uranus can be found in the east and Neptune in southeast at dawn.

Venus sets at 11:00 p.m. local daylight time. Mars sets at 3:00 a.m. local daylight time. Saturn transits at 11:00 p.m. and sets at 5:00 a.m. local time at midmonth, for observers at latitude 40 degrees north.

Mercury reaches superior conjunction on May 27. This apparition favors southern hemisphere observers. The speedy planet brightens from magnitude -0.1 to magnitude -1.5, as it decreases in apparent size from 6.4 to 5.2 arc seconds.

Venus shines at its maximum brilliance early this month. It sets 3.5 hours after the Sun. Venus continues to decline in phase and ends the month less than one per cent illuminated. However, it swells to almost one arc minute in apparent size by that time. Venus is 0.8 degree south of the second-magnitude star Alnath (Beta Tauri) on May 6. A thin crescent Moon passes five degrees south of Venus on the evening of May 22.

Mars begins the month at magnitude 0.0 but fades to magnitude 0.5 by the end of May. It shrinks 20% in apparent size during the course of the month. The Red Planet is six degrees east of the first-magnitude star Regulus (Alpha Leonis) on May 1 but finishes May almost fifteen degrees to the southeast of Leo's lucida. Mars is more than one astronomical unit from the Earth on May 8.

Jupiter is in conjunction with the Sun on May 13 and, as a result, is not visible this month.

Saturn decreases in brightness from magnitude 0.3 to magnitude 0.5. During May, Saturn's ring plane is inclined by 13 degrees. Its rings subtend 43 arc seconds. As Saturn retrogrades through Virgo, it remains within five degrees of the first-magnitude star Spica for the entire month. Eighth-magnitude Titan is due south of Saturn on the evenings of May 4 and May 20. Saturn's brightest satellite is due north of the planet on the evenings of May 12 and May 28. Prior to midnight on May 14, eleventh-magnitude Iapetus is two arc minutes north of Saturn. A star of similar brightness, GSC 4972:631, is situated between Iapetus and Saturn. For further information on Saturn's satellites, browse http://www.skyandtelescope.com/observing/objects/javascript/3308506.html

Uranus rises shortly before 3:00 a.m. local daylight time. It travels from Cetus to Pisces during May and can be found one degree northeast of the sixth-magnitude star 44 Piscium by the end of the month.

Neptune is observable during morning twilight by the middle of May. It lies approximately three degrees south of the fourth-magnitude star Theta Aquarii and two degrees east of the fifth-magnitude star e Aquarii (38 Aquarii). Nereid, Neptune's third-largest satellite, was discovered on May 1, 1949 by Gerard Kuiper.

Pluto lies in northern Sagittarius, less than two degrees east of the open cluster M25. The fourteen-magnitude dwarf planet can be found one half of a degree east of the seventh-magnitude star SAO 161665 on May 1 and just three arc minutes south of that same star on the morning of May 31.

Comet C/2009 P1 (Garradd) dims to tenth-magnitude this month as it passes from Lynx into Cancer. It lies than one degree west of the tenth-magnitude spiral galaxy NGC 2683 on the evenings of May 10 and May 11. On the evenings of May 24 and May 25, the comet passes between the fifth-magnitude stars Rho1 and Rho2 Cancri. Visit http://cometchasing.skyhound.com/ for additional information on this and other comets visible during May.

Asteroid 5 Astraea shines at magnitude 10.9 as it travels southeastward through Leo and Virgo during May. This small main-belt asteroid passes one half of a degree south of the fifth-magnitude star Iota Leonis on the nights of May 11 and May 12 and one half of a degree northwest of the fifth-magnitude star Omega Virginis on the night of May 31. Data on asteroid occultations taking place in May is available at http://www.asteroidoccultation.com/2012_05_si.htm

During May, nine stars (Capella, Pollux, Procyon, Regulus, Spica, Arcturus, Antares, Vega, and Deneb) and three planets (Venus, Mars, and Saturn) with magnitudes brighter than 1.5 are visible in the early part of the night.

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

The famous eclipsing variable star Algol (Beta Persei) is at a minimum, decreasing in magnitude from 2.1 to 3.4, on May 2, 5, 8, 11, 13, 16, 19, 22, 25, 28, and 31. For more on Algol, see http://stars.astro.illinois.edu/sow/Algol.html and http://www.solstation.com/stars2/algol3.htm

Binary and Multiple Stars for May

1 Bootis, Struve 1782, Tau Bootis, Struve 1785, Struve 1812 (Bootes); 2 Canum Venaticorum, Struve 1624, Struve 1632, Struve 1642, Struve 1645, 7 Canum Venaticorum, Alpha Canum Venaticorum (Cor Caroli), h2639, Struve 1723, 17 Canum Venaticorum, Otto Struve 261, Struve 1730, Struve 1555, h1234, 25 Canum Venaticorum, Struve 1769, Struve 1783, h1244 (Canes Venatici); 2 Comae Berenices, Struve 1615, Otto Struve 245, Struve 1633, 12 Comae Berenices, Struve 1639, 24 Comae Berenices, Otto Struve 253, Struve 1678, 30 Comae Berenices, Struve 1684, Struve 1685, 35 Comae Berenices, Burnham 112, h220, Struve 1722, Beta Comae Berenices, Burnham 800, Otto Struve 266, Struve 1748 (Coma Berenices); h4481, h4489, Struve 1604, Delta Corvi, Burnham 28, h1218, Struve 1669 (Corvus); H N 69, h4556 (Hydra); Otto Struve 244, Struve 1600, Struve 1695, Zeta Ursae Majoris (Mizar), Struve 1770, Struve 1795, Struve 1831 (Ursa Major); Struve 1616, Struve 1627, 17 Virginis, Struve 1648, Struve 1658, Struve 1677, Struve 1682, Struve 1689, Struve 1690, 44 Virginis, Struve 1719, Theta Virginis, 54 Virginis, Struve 1738, Struve 1740, Struve 1751, 81 Virginis, Struve 1764, Struve 1775, 84 Virginis, Struve 1788 (Virgo)

Notable carbon star for May: SS Virginis

Top ten deep-sky objects for May: M3, M51, M63, M64, M83, M87, M104, M106, NGC 4449, NGC 4565

Top ten deep-sky binocular objects for May: M3, M51, M63, M64, M84, M86, M87, M104, M106, Mel 111

Challenge deep-sky object for May: 3C 273 (Virgo)

The objects listed above are located between 12:00 and 14:00 hours of right ascension.