After the lovely “evening star” Venus follows the Sun down to the western horizon on cool September evenings, another dazzling planet rises in the east to take her place. It is the giant planet Jupiter, largest of the planets in our solar system and second only to Venus in dazzling brightness. Jupiter will dominate our evening sky for the remainder of the year, shining near the Circlet asterism in the constellation of Pisces.
Jupiter appears exceptionally bright in our sky this month, not only because of its colossal size (it could swallow 1000 Earths), but also because it is at its closest point to the Earth for 2010. Earth has a close encounter with Jupiter every 13 months when our faster moving planet gains a lap on sluggish Jupiter as we both race around the Sun. The night of closest approach is called opposition because, as seen from Earth, Jupiter is exactly opposite the Sun in our sky, rising in the east as the Sun sets in the west and then setting in the west just as the Sun rises in the east. The celestial geometry of opposition is just like that of the full moon.
On the night of September 21, Jupiter will stand in opposition to the Sun at a distance of 368-million miles from Earth. The nearly full Harvest Moon will be shining nearby but it will hardly diminish Jupiter’s brilliance.
Just by coincidence, the much more distant planet Uranus will reach its opposition to the Sun the very same night that Jupiter does. Uranus will lie 1780-million miles from Earth and shine as a very faint fifth magnitude star. Under dark-sky conditions, Uranus can be glimpsed with the unaided eye, but the bright moonlight on the night of opposition will make spotting Uranus nearly impossible. It will be better to wait several nights later when the Moon is out of the way. By September 28 or 29, Jupiter and Uranus will rise in a dark sky together and a keen-eyed observer just might make out the distant planet Uranus about one degree to Jupiter’s upper left.
An ordinary pair of binoculars will make spotting Uranus a snap.
If held very steady or supported on a tripod, those same binoculars might also reveal up to four of Jupiter’s largest moons, Io, Europa, Ganymede, and Callisto.
A small telescope at low power should provide a striking view of the two giant planets and four giant moons. Remember, though, most telescopes invert their image, so look for Uranus to Jupiter’s lower right through your telescope. Telescopically, Jupiter will look like a big, bright ball with one or more dark stripes running across it. Uranus, on the other hand, will look like a tiny, pale-green disk, much smaller than Jupiter.
This unusual double opposition of Jupiter and Uranus won’t repeat itself until the year 2037. ***
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Also, check out Jimmy’s astrophotography website at www.jwestlake.com.