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Observing Highlights for May: A Rare Planetary Trio

May 2013 Venus_Jupiter_Aldebaran_ChumackHRwebIf lack of binoculars or a telescope shut you out of April’s big viewing event, the two comets, May will be a much easier treat. Three planets, Jupiter, Venus, and Mercury, meet in the western sky after sunset, coming within five degrees of each other in what astronomers call a trio. The gathering of three planets is rather unique, and the next trio won’t occur until October 2015.

Jupiter has been high in the west after sunset all year, and as May opens it is clearly beginning to sink toward the horizon with the winter constellations that surround it. But Venus is coming to greet it
before it disappears near the sun. Venus has to contend with the glow of sunset as it lugs itself upward each night. On May 10, can you spot Venus just two degrees away from a newborn crescent moon? On the next night the crescent moon will appear about halfway between Jupiter and Venus.
By mid-May, Venus becomes easier to see and its motion toward Jupiter is obvious, but behind it near the horizon a dimmer planet is entering the race. Mercury, hiding in the colors of sunset, is moving faster than Venus as the three huddle low on the horizon. By May 23, Mercury has pulled alongside Venus as the pair come within two degrees of each other. Bright Venus at magnitude -3.9 is a guide to finding Mercury beside it at magnitude -1.

A planetary trio officially occurs when three planets are within five degrees of each other, and Mercury, Venus, and Jupiter maintain this for the evenings spanning May 24 to May 29. On May 24, Mercury and Venus are still less than two degrees apart. On May 25, the three planets have moved to within three degrees of each other, with Jupiter to the upper left, Mercury to the right, and Venus below. May 26 finds the three planets still within three degrees of each other with their positions shifted slightly as Mercury has moved higher. On May 27, Jupiter and Venus will be side by side with Mercury just above. On May 28, Venus will be one degree to the upper right of Jupiter, with Mercury still above. The last night of the planetary trio, May 29, reveals the three in a line with Mercury highest and having dimmed to magnitude -0.5, Venus at magnitude -3.9, and Jupiter below at magnitude -1.9. The trio ends as the three stretch apart and Jupiter falls down into the sun’s glare. Mercury will continue to dim as it rises.

The Eta Aquarid meteor shower, with approximately 45 meteors an hour, peaks over the weekend of May 4 and 5. Eta Aquarids get their name because they appear to come from the constellation Aquarius near the star Eta. This shower is one of two annual showers whose source is Halley’s Comet.

An annular solar eclipse is slated for May 9 and 10 over Australia and the Pacific Ocean. Annular eclipses do not block the entire light from the sun because the moon is too far from Earth, leaving a ring of light around the moon. Therefore they cannot be viewed with proper eye protection. The partial phase begins on May 9 at 22:22 UT, with the annular event beginning May 10 at 00:22 UT. Maximum eclipse occurs May 10 at 00:25 UT and the annular phase ends at 00:28 UT. The partial phase of the eclipse wraps up on May 10 at 2:30 UT.

The moon in May passes a few notable objects as it waxes toward full. On May 21 it nears Spica and on May 22 the moon is near Saturn. The moon reaches its peak of fullness on different calendar dates depending on where you live. For those on the East Coast of the US, the moon is full on May 25 just after midnight, 12:25 a.m. But for those in the central time zone and west, the moon is officially full a "day" earlier, on May 24.

(Photo: This grouping of Venus, Jupiter, and the star Aldebaran occurred in 2012. Credit: John Chumack)

HS_KellyWhittKelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.

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