By Dave Mitsky
All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)
5/2 Last Quarter Moon occurs at 11:14
5/4 Neptune is 6 degrees south of the Moon at 7:00; the Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to begin at 0:58
5/5 The peak of the Eta Aquarid meteor shower (20 per hour for northern observers) occurs at 6:00; May Day or Beltane, a cross-quarter day, occurs at 20:30
5/7 Uranus is 4 degrees south of the Moon at 0:00
5/10 Venus is at the ascending node today; New Moon (lunation 1118), with an annular eclipse visible from the central Pacific and Australia already underway, occurs at 00:28; asteroid 2 Pallas is in conjunction with the Sun at 21:00
5/11 Mercury is at the ascending node today; Mercury is in superior conjunction at 21:00
5/12 Jupiter is 3 degrees north of the Moon at 13:00
5/13 The Moon is at apogee, subtending 29’26″ from a distance of 405,825 kilometers (252,168 miles), at 14:00
5/16 Mercury is at perihelion today
5/17 The Lunar X (also known as the Werner or Purbach Cross), an X-shaped illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to begin at 10:56;
5/18 First Quarter Moon occurs at 4:34
5/22 The Moon is 0.005 degrees north of the first-magnitude star Spica (Alpha Virginis), with an occultation taking place in the Pitcairn Islands, French Polynesia, Melanesia, northeast Australia, Indonesia, the Philippines, and southeast Asia, at 11:00
5/23 Saturn is 4 degrees north of the Moon at 10:00; asteroid 6 Hebe (magnitude 9.6) is at opposition at 19:00
5/25 Mars is at the ascending node today; Mercury is 1.4 degrees north of Venus at 3:00; an extremely shallow penumbral lunar eclipse theoretically visible from the western hemisphere begins at 3:53; Full Moon, known as the Milk or Planting Moon, occurs at 4:25
5/26 Mercury is at its greatest heliocentric latitude north today; the Moon is at perigee, subtending 33’20″ from a distance of 358,377 kilometers (222,686 miles), at 2:00
5/27 Mercury is 2 degrees north of Jupiter at 9:00
5/28 Venus is 1.0 degree north of Jupiter at 20:00
5/31 Last Quarter Moon occurs at 18:58
Nicolas Lacaille (1713-1762) and Joseph Lockyer (1836-1920) were born this month.
Nereid, Neptune’s third-largest satellite, was discovered on May 1, 1949 by Gerard Kuiper.
The peak of the Eta Aquarid meteor shower occurs during a waning crescent Moon and is not compromised by moonlight. Southern hemisphere observers are favored and may see as many as 55 meteors per hour. Eta Aquarid meteors are debris from the famous periodic comet 1P/Halley.
The Moon is located in Sagittarius and is 20.6 days old on May 1 at 0:00 UT. The Moon is at its greatest northern declination on May 12 (+20.2 degrees) and its greatest southern declination on May 26 (-20.2 degrees). Longitudinal libration is at maximum (+6.2 degrees) on May 4 and at minimum (-7.4 degrees) on May 20. Latitudinal libration is at maximum (+6.9 degrees) on May 17 and at minimum (-6.8 degrees) on May 2 and (-6.8 degrees) on May 30. The night of May 18 is an ideal time to see Rupes Recta, the Straight Wall. The first-magnitude star Spica is occulted by the Moon on May 22. The almost Full Moon occults the second-magnitude star Beta Scorpii for most of the eastern United States on the evening of May 2. See http://www.lunar-occultations.com/iota/bstar/0522zc1925.htm and http://www.lunar-occultations.com/iota/bstar/0525zc2302.htm for information on these two lunar occultations. A minor penumbral eclipse occurs on May 25, as described on page 52 of the May issue of Sky & Telescope. Mid-eclipse happens at 4:10 UT. Large tides will take place from May 25 through May 28. 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 2013 takes place on May 10. This annular solar eclipse, the 31st eclipse of Saros 138, can be seen from Australia, eastern Papua New Guinea, the Solomon Islands, and the Gilbert Islands. Greatest eclipse occurs at 00:26:20 UT, at which time the duration of annularity will be six minutes and three seconds. For further information on this event, consult http://eclipse.gsfc.nasa.gov/OH/OH2013.html#SE2013May10A and page 52 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 -1.0, 5.2″, 91% illuminated, 1.28 a.u., Pisces), Venus (magnitude -3.9, 9.8″, 99% illuminated, 1.70 a.u., Aries), Mars (magnitude 1.3, 3.8″, 100% illuminated, 2.45 a.u., Aries), Jupiter (magnitude -2.0, 33.6″, 100% illuminated, 5.88 a.u., Taurus), Saturn (magnitude 0.1, 18.8″, 100% illuminated, 8.82 a.u., Libra), Uranus on May 16 (magnitude 5.9, 3.4″, 100% illuminated, 20.76 a.u., Pisces), Neptune on May 16 (magnitude 7.9, 2.3″, 100% illuminated, 30.14 a.u., Aquarius), and Pluto on May 16 (magnitude 14.1, 0.1″, 100% illuminated, 31.73 a.u., Sagittarius).
In the evening, Mercury, in late May, and Venus, in mid-May, can be seen in the northwest, Jupiter in the west, and Saturn in the southeast. Saturn in located in the south at midnight. Saturn is in the west, Uranus in the east, and Neptune in the southeast at dawn.
Venus is visible during evening twilight, Jupiter sets at 10:00 p.m. local daylight time, and Saturn transits the meridian at 12:00 a.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 11 and reappears in the evening sky by May 18. The speediest planet lies seven degrees north of the first-magnitude star Aldebaran on May 21, 1.4 degrees north of Venus on May 25, and two degrees north of Jupiter on May 27. Mercury, Venus, and Jupiter lie within three degrees of one another in the west-northwest from May 25 through May 27 and within two degrees of one another on May 26 and May 27. The three planets are closest and form a nearly equilateral triangle on May 26. They form a trio, a temporary group of three celestial objects fitting within a circle with a diameter of five degrees, from May 24 to May 29. The three planets are greater than six degrees above the horizon 30 minutes after the Sun sets for observers at 40 degrees north. By May 31, the three planets no longer form a triangle.
Venus begins a rather poor apparition for northern hemisphere observers. It sets in the west-northwest about 45 minutes after the Sun. Venus and Mercury are at their closest, just a bit more than a degree apart, on May 24.
Mars is not observable this month.
Jupiter drops almost one degree lower in the sky with each passing night. The waxing crescent Moon and Jupiter are close neighbors on the evenings of May 11 and May 12. Jupiter and Mercury are closest on the evening of May 26. The King of the Planets is just one degree from Venus on May 28.
Uranus is positioned low in the east in Pisces at dawn. It lies four degrees south-southeast of the fourth-magnitude star Delta Piscium at the end of the month.
Neptune is observable during morning twilight by the middle of May. The gas giant is positioned less than one degree north of the fifth-magnitude star Sigma Aquarii.
Pluto lies in northern Sagittarius, less than one half degree to the southeast of the sixth-magnitude star HP 92079 and about two degrees to the southwest of the faint open cluster NGC 6716. A finder chart is available at http://dcford.org.uk/findercharts/22pluto_2013_2.pdf
As it travels northwestward through Cepheus and Ursa Minor this month, Comet C/2011 L4 (PanSTARRS) dims to seventh magnitude. It passes a few degrees to the west of the ancient open cluster NGC 188 on May 25 and May 26. The comet is edge-on with respect to the Earth on the nights of May 27 and May 28. Visit http://cometchasing.skyhound.com/ for additional information on this and other comets visible during May.
Asteroid 1 Ceres glides through Gemini during May. It passes less than one degree north of the fourth-magnitude star Iota Geminorum on the nights of May 26 and May 27. Information on asteroid occultations taking place this month is available at http://www.asteroidoccultation.com/2012_05_si.htm
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 1, 4, 7, 10, 13, 15, 18, 21, 24, 27, and 30. For more on Algol, see http://stars.astro.illinois.edu/sow/Algol.html and http://www.solstation.com/stars2/algol3.htm
As of this month, the separation of the A and B components of the well-known binary star Porrima (Gamma Virginis) has increased to 2.0 arc seconds.
Eighty 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
One hundred and sixty-five deep-sky objects for May: NGC 5248 (Bootes); M3, M51, M63, M94, M106, NGC 4111, NGC 4138, NGC 4143, NGC 4151, NGC 4214, NGC 4217, NGC 4244, NGC 4346, NGC 4369, NGC 4449, NGC 4485, NGC 4490, NGC 4618, NGC 4631, NGC 4656, NGC 4868, NGC 5005, NGC 5033, NGC 5297, NGC 5353, NGC 5354, Up 1 (Canes Venatici); Mel 111, M53, M64, M85, M88, M91, M98, M99, M100, NGC 4064, NGC 4150, NGC 4203, NGC 4212, NGC 4251, NGC 4274, NGC 4278, NGC 4293, NGC 4298, NGC 4302, NGC 4314, NGC 4350, NGC 4414, NGC 4419, NGC 4448, NGC 4450, NGC 4459, NGC 4473, NGC 4474, NGC 4494, NGC 4559, NGC 4565, NGC 4651, NGC 4689, NGC 4710, NGC 4725, NGC 4874, NGC 5053 (Coma Berenices); NGC 4027, NGC 4038-9, NGC 4361 (Corvus); M68, M83, NGC 4105, NGC 4106, NGC 5061, NGC 5101, NGC 5135 (Hydra); M40, NGC 4036, NGC 4041, NGC 4051, NGC 4062, NGC 4085, NGC 4088, NGC 4096, NGC 4100, NGC 4144, NGC 4157, NGC 4605, NGC 5308, NGC 5322 (Ursa Major); M49, M58, M59, M60, M61, M84, M86, M87, M89, M90, M104, NGC 4030, NGC 4073, NGC 4168, NGC 4179, NGC 4206, NGC 4215, NGC 4216, NGC 4224, NGC 4235, NGC 4260, NGC 4261, NGC 4267, NGC 4281, NGC 4339, NGC 4343, NGC 4365, NGC 4371, NGC 4378, NGC 4380, NGC 4387, NGC 4388, NGC 4402, NGC 4429, NGC 4435, NGC 4438, NGC 4517, NGC 4526, NGC 4535, NGC 4536, NGC 4546, NGC 4550, NGC 4551, NGC 4567, NGC 4568, NGC 4570, NGC 4593, NGC 4596, NGC 4636, NGC 4638, NGC 4639, NGC 4643, NGC 4654, NGC 4666, NGC 4697, NGC 4698, NGC 4699, NGC 4753, NGC 4754, NGC 4760, NGC 4762, NGC 4866, NGC 4900, NGC 4958, NGC 5044, NGC 5054, NGC 5068, NGC 5077, NGC 5084, NGC 5087, NGC 5147, NGC 5170, NGC 5247, NGC 5363, NGC 5364 (Virgo)
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.