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May 2011 Celestial Calendar & Observing Notes c/o Dave Mitsky


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May 2011 Celestial Calendar & Observing Notes courtesy of Dave Mitsky (calendar data also reproduced in our forum calendar).

All times, unless otherwise noted, are UT.

5/1 May Day or Beltane, a cross-quarter day; Mercury is 8 degrees south of the Moon at 7:00; Mars is 0.4 degree north of Jupiter at 11:00; Jupiter is 6 degrees south of the Moon at 19:00; Mars is 6 degrees south of the Moon at 20:00

5/3 New Moon (lunation 1093) occurs at 6:51

5/6 The peak of the Eta Aquarid meteor shower (20/hour) occurs at 12:00

5/7 The Moon is 1.7 degrees south of the bright open cluster M35 in Gemini at 7:00; Mercury is at greatest western elongation (27 degrees) at 19:00

5.8 Mercury is 1.4 degrees south of Venus at 3:00

5/10 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 05:56; First Quarter Moon occurs at 20:33; Mercury is 2 degrees south of Jupiter at 22:00

5/11 Venus is at its greatest heliocentric latitude south today; Venus is 0.6 degree south of Jupiter at 9:00

5/13 Asteroid 10 Hygiea (magnitude 9.2) is at opposition at 10:00

5/14 Saturn is 8 degrees north of the Moon at 15:00; a double Galilean satellite transit (Io follows Europa) occurs at 18:41

5/15 The Moon is at perigee, subtending 33 arc minutes from a distance of 362,135 kilometers (225,020 miles), at 11:24

5/17 Full Moon, known as the Milk or Planting Moon, occurs at 11:09

5/18 A double Galilean satellite transit (Io follows Europa) occurs at 7:39; Mercury is 1.4 degrees south of Venus at 8:00

5/19 Mercury is at its greatest heliocentric latitude south today

5/20 Mercury is 2 degrees south of Mars at 1:00

5/21 A double Galilean satellite transit (Io follows Europa) occurs at 20:36

5/22 Venus is 1.1 degrees south of Mars at 15:00

5/24 Last Quarter Moon occurs at 18:52; Neptune is 6 degrees south of the Moon at 18:00

5/25 A double Galilean satellite transit (Io follows Europa) occurs at 9:33; asteroid 2 Pallas (magnitude 9.2) is stationary at 15:00

5/26 The Curtiss Cross, an X-shaped illumination effect located between the craters Parry and Gambart, is predicted to begin at 6:26

5/27 The Moon is at apogee, subtending 29 arc minutes from a distance of 404,003 kilometers (251,657 miles), at 9:57; Uranus is 6 degrees south of the Moon at 13:00

5/28 A double Galilean satellite transit (Io follows Europa) occurs at 22:30

5/29 Jupiter is 6 degrees south of the Moon at 15:00

5/30 Mars is 4 degrees south of the Moon at 20:00

5/31 Venus is 4 degrees south of the Moon at 4:00

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

The peak of the Eta Aquarid meteor shower on May 6 is not affected by moonlight. This shower favors southern observers. Eta Aquarid meteors are debris from the famous periodic comet 1P/Halley.

The Moon is located in Pisces and is 27.3 days old on May 1 at 0:00 UT. At dawn on May 1, in order of decreasing altitude, the thin crescent Moon, Venus, Mercury, and a close pairing of Mars and Jupiter may be visible through binoculars shortly before sunrise. A waning crescent Moon joins those planets once again in the dawn sky from May 29 to May 31. The Moon is at its greatest northern declination on May 6 (+23.4 degrees) and its greatest southern declination on May 18 (-23.4 degrees). Longitudinal libration is at maximum (+6.4 degrees) on May 21 and at minimum (-6.6 degrees) on May 8. Latitudinal libration is at maximum (+6.8 degrees) on May 13 and at minimum (-6.9 degrees) on May 26. See http://www.lunar-occultations.com/iota/planets/0516venus.htm for information on lunar occultations. Visit Extreme Lunar Crescent Data [L1093-1104] | 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 Aries on May 1.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on May 1: Mercury (magnitude 0.8, 9.2", 31% illuminated, 0.73 a.u., Pisces), Venus (magnitude -3.8, 11.6", 88% illuminated, 1.43 a.u., Pisces), Mars (magnitude 1.2, 4.0", 99% illuminated, 2.32 a.u., Pisces), Jupiter (magnitude -2.1, 33.4", 100% illuminated, 5.90 a.u., Pisces), Saturn (magnitude 0.5, 19.1", 100% illuminated, 8.72 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).

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

At midmonth, Mercury can be seen at morning twilight by observers at latitude 40 degrees north. Venus, Mars, and Jupiter rise at 5:00 a.m., and Saturn transits at 10:00 p.m. and sets at 4:00 a.m. local time at midmonth for people living at latitude 40 degrees north.

May is a very favorable month for observing planetary close encounters. Mercury, Venus, Mars, Jupiter, and Uranus are all located in Pisces during early May. The first four of those planets lie within a ten-degree circle for the first three weeks of the month. Between May 7 and May 15, they are less than eight degrees apart. Mercury, Venus, Mars, and Jupiter fit into a circle having a diameter of six degrees on May 12. Two planetary trios, i.e., three planets within five degrees of each other, take place this month. The Jupiter-Venus-Mercury trio is 2.1 degrees in diameter on May 7 and May 15. The three planets lie within three degrees of each from May 9 to May 13. The Venus-Mercury-Mars trio lasts for 10 days and is the tighter of the two, spanning a bit more than two degrees on May 21. Mercury, Venus, and Mars lie within three degrees of each other from May 19 to May 23.

Mercury reaches greatest western elongation on May 7. This apparition favors southern hemisphere observers. The speedy planet brightens from magnitude 0.8 to magnitude -0.9 as it decreases in apparent size from 9.2 to 5.5 arc seconds.

Venus is also better seen from the southern hemisphere due to the angle of the ecliptic. Venus and Mercury lie within 1.5 degrees of each for a remarkable two weeks beginning on May 7. The two planets are no farther than two degrees apart from May 4 through May 22. Brilliant Venus passes 0.6 degree south of Jupiter on May 11, one degree south of Mars on May 22, and four degrees south of the Moon on May 31. In mid-May, it shines at magnitude -3.8 but subtends only 11 arc seconds.

Mars shines faintly at magnitude 1.2 and is 0.4 degree north of Jupiter on May 1 and one degree north of Venus on May 22.

Jupiter is positioned low in the morning sky at the beginning of May. Southern hemisphere observers are favored once again. Jupiter shines at magnitude -2.1 and spans 33.9 arc seconds on May 15. Click on Transit Times of Jupiter's Great Red Spot - Planets - SkyandTelescope.com to determine transit times of the central meridian by the Great Red Spot. Data on the Galilean satellites is available at Jupiter's Moons Javascript Utility - Interactive Observing Tools - SkyandTelescope.com

This month Saturn grows ever closer to the third-magnitude binary star Gamma Virginis, as the planet retrogrades through Virgo. It decreases in magnitude 0.5 to magnitude 0.7. During May, Saturn’s ring plane achieves an inclination of eight degrees. Saturn’s rings subtend 43 arc seconds. Eighth-magnitude Titan is due south of Saturn on May 3 and May 19. Saturn’s brightest satellite is due north of the planet on May 11 and May 27. On the morning of May 22, Titan, Rhea, and Tethys are situated to the west of Saturn and Enceladus and Dione to the east. Eleventh-magnitude Iapetus is close to the planet on the night of May 22. For further information on Saturn’s satellites, browse Saturn's Moons Javascript Utility - Interactive Observing Tools - SkyandTelescope.com

Uranus is located in southern Pisces but is only 15 degrees above the horizon at dawn by the end of May.

Neptune is positioned less than half a degree to the southeast of 38 Aquarii for the entire month. It rises about 3:00 a.m. local daylight time at the start of the month. Nereid, Neptune’s third-largest satellite, was discovered on May 1, 1949 by Gerard Kuiper.

This month Pluto is located in northern Sagittarius, less than two degrees to the southeast of the open cluster M25. It rises at approximately 11:00 p.m. local time by the middle of the month. Pluto passes just north of the star SAO 161540 (magnitude 5.6) on May 5. The dwarf planet travels westward at approximately 0.9 arc minute per day.

The tenth-magnitude comet C/2009 P1 (Garrad) glides northward through Aquarius this month. It passes by the sixth-magnitude stars 81 and 82 Aquarii between May 17 and May 20. Visit Comet Chasing for additional information on this and other comets visible during May.

Asteroid 10 Hygiea reaches opposition on May 13. From May 6 to May 22, this C-type asteroid will shine at magnitude 9.2, as it passes northwestward through southern Libra. Asteroid 7 Iris shines a bit less brightly at tenth-magnitude, as it travels through southern Cancer. It passes quite close to 45 Cancri on May 10, just north of the open cluster M67 on May 17, and only four arc minutes south of the fourth-magnitude star Alpha Cancri on May 22. Information on stellar occultations by asteroid 217 Eudora on the morning of May 29 and by asteroid 4569 Baerbel on the morning of May 30 can be found at Monthly Index of Asteroid Occultation Path Predictions

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

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