The last morning of August 2013 presents a most picturesque pairing of the moon and giant planet Jupiter in the hours before sunrise. Look east in the predawn darkness – or even as dawn breaks – to behold these two very bright worlds. You can’t miss them, if it’s clear. The waning crescent moon and dazzling Jupiter now rank as the brightest and second-brightest celestial bodies, respectively, in the early morning sky. The moon is now moving downward the eastern predawn sky each morning, appearing as a slimmer crescent each day as it wanes toward new moon on September 5. Both Mars and Jupiter are in the predawn sky, and the moon will pass near both planets. The moon is closest to Jupiter on the morning of August 31.
It’s true the planet Venus is brighter than Jupiter. Venus is the brightest planet. But Venus isn’t up before dawn now; it’s in the western sky shortly after sunset. At mid-northern latitudes, Venus sets about one and one-half hours after the sun, or as dusk is finally giving way to night. Be sure circle September 8 on your calendar, though, to watch the upcoming conjunction of the waxing crescent moon and Venus in the evening sky.
Back to the morning sky on August 31. Wake up before dawn – or one to one and one-half hours before sunrise – to view the much fainter red planet Mars below Jupiter. At mid-northern latitudes, the Gemini stars, Castor and Pollux, shine to the left of Jupiter. The star Pollux more or less makes a right angle with Jupiter and Mars.
If you have telescope – even a modest backyard telescope – take closer look at the planet Jupiter tomorrow morning. As seen from North America, the Galilean moons – Jupiter’s four major moons – are to one side of Jupiter. As seen from North America on the morning of August 31, in their order outward from Jupiter, the moons are Callisto, Io, Ganymede and Europa. Their true order going outward from Jupiter in their respective orbits: Io, Europa, Ganymede and Callisto.
To find out the locations of Jupiter’s moons for any date and time, check out this handy guide, courtesy of skyandtelescope.com. Io and Europa are about the same size as our moon, while the diameters of Callisto and Ganymede span about one-and-a-half times the moon’s diameter.
Bottom line: On Saturday, August 31, 2013, see a beautiful pairing of the waning crescent moon and the giant planet Jupiter! Then keep watching as the moon continues to wane to a slimmer crescent phase in the eastern predawn sky.