POSTED: 1:30 a.m. HST, Apr 24, 2011
LAST UPDATED: 9:02 p.m. HST, Aug 5, 2011
The most remarkable astronomy event this May is a gathering of planets in the predawn sky.
Four of the five naked-eye planets will take part in the predawn show: Venus, Jupiter, Mercury and Mars.
These planets don't rise until around 5 a.m., and day starts to break around 5:30 a.m., so your viewing window is only about 30 minutes. You'll also need a clear view of the east, since the newly risen planets will be quite low at daybreak. Looking east over the sea is ideal.
Since the lineup changes as the month goes on, here are a few "snapshots" of what you'll see on different days of the month:
» May 1: At 5:20 a.m., look for blazing Venus (minus 3.9 magnitude) about 10 degrees above the eastern horizon. That's about the width of a fist at arm's length. Mercury will be 3 degrees below Venus, shining brightly at magnitude 0.9. You might be able to also catch Jupiter here in early May, shining down below Mercury at minus 2 magnitude. However, Jupiter is barely above the eastern horizon as day breaks. You will need binoculars to see faint Mars, just left of Jupiter.
» May 5: Look for Venus about 8 degrees above the eastern horizon at 5:10 a.m. Eight degrees is the width of four fingers held at arm's length. Mercury is only 1.5 degrees below Venus, and shines at 0.6 magnitude. Down near the horizon, Jupiter shines at minus 2 magnitude, brighter than any dot of light except Venus. And finally, reddish Mars is about 2 degrees below, and to the left of, Jupiter. Mars is still only 1st magnitude, so it will remain hard to see in the dawn light without binoculars.
Between May 5 and May 10, Jupiter will appear ever closer to Venus.
» May 11: Venus and Jupiter, the two brightest dots of light in the sky, will be right next to each other. At about 5:10 a.m., Venus and Jupiter will be about 10 degrees above the eastern horizon. The two planets are only about half a degree apart, which is about the diameter of the full moon. Jupiter is the one at the left; at minus 2 magnitude, it's very bright, but not as bright as Venus at minus 3.9. Look for Mercury about 1.5 degrees to the lower right of Venus. Dim Mars is about 5 degrees below, and to the left of, Venus.
Over the next 10 days, Jupiter will appear higher in the sky each morning, while the other three planets will hunker down near the horizon.
» May 20: Look for Jupiter by its lonesome in the east at 5 a.m., about 15 degrees above the eastern horizon. Then look for the other three planets clustered into a tight triangle to the lower left of Jupiter. Venus forms the top of the triangle, shining at minus 3.9. Mercury, now up to minus 0.14, is 2 degrees to the lower right of Venus; Mars is to the left of Venus.
For the rest of the month the planets will appear to move apart, and by the end of the month they'll form a string of pearls.
» May 28-31: At 5 a.m. our four planets now look like a string of pearls, with Jupiter at the top. Jupiter, 20 degrees above the east horizon, shines at minus 2.1. Nearer to the horizon, look for Venus, bright as always. Mars (1.3 magnitude) is above Venus, Mercury (minus 0.7 magnitude) is below Venus.
Saturn is the one loner in the evening. While the other planets gather in the morning sky, Saturn remains a beacon in the evening sky throughout the month. The planet shines at 0.8 magnitude, somewhat brighter than the star Spica (the bright bluish star just below Saturn).
This is a light meteor shower caused by debris from Halley's Comet, with as many as 10 meteors an hour. The peak occurs on the evening of May 5-6 (i.e., stay up late on May 5 and look for meteors into the early hours of May 6). The shower is active May 4-7. There is no interference from the moon, which is waxing crescent and sets early in the evening.
The southern sky contains some of the most interesting stars here in May.
May is a prime time to catch the Southern Cross in the Hawaiian night sky. The Southern Cross is officially known as "Crux" (Latin for "Cross"), and that's how it's labeled on the star map. The bottom star, Acrux, is quite bright; the top star, Gacrux, and the star that marks the left side of the crossbar (Mimosa) are also bright. However, the star that marks the right side of the crossbar (Delta Crucis) is significantly fainter; if you are trying to find the Cross in the city, the tricky part is finding that star.
Fortunately, we have two "helper stars" on the map to guide your way to the Southern Cross: Alpha and Beta Centauri are just to the left. These two bright stars are generally easier to spot than the Cross itself. Once you find them, just go right from Alpha and Beta Centauri and you'll come to the crossbar of the Southern Cross.
Scorpius has also returned to our sky. The distinctive constellation really does look like a scorpion.
Leo the Lion is partway down the western sky. To the east of Leo is Spica, the bright bluish star in the otherwise faint constellation of Virgo. Saturn appears close to Spica this year.
In the northern sky, the famous Big Dipper is high in the north. The pointer stars of the Big Dipper — the two stars in the cup that don't have the handle attached — point to the North Star.
Mike Shanahan is director of Education, Exhibits and Planetarium at Bishop Museum. Reach him at firstname.lastname@example.org.