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发表于 2006-4-15 12:11:09
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猎手与牛
The hunter and bull
On a cold December morning, Wally Pacholka imaged the constellations Orion (left) and Taurus (right). He photographed the hunter and bull from Joshua Tree National Park in California.
土星
Saturn shines
Saturn remains visible all evening during April. On the 1st, it doesn't set until 5 A.M. local time, but it dips below the horizon 2 hours earlier by the 30th. Shining at magnitude 0.2, it's easily the brightest object in Cancer the Crab. Binoculars will show the Beehive star cluster (M44) just 3° east of Saturn. A waxing gibbous Moon joins the pair April 6, when it passes 4° north of the planet.
When viewed through a telescope, you should notice Saturn appears about 10-percent smaller than it did at opposition in late January. The planet's disk extends 19" at midmonth, while the ring system's long axis spans 42". As you view the rings, note the dark Cassini Division, which separates the outer A ring from the brighter B ring. You also should see the planet's shadow falling on the rings just east of the globe.
Any scope also reveals Saturn's largest moon, Titan. Glowing at magnitude 8.4, it can be spotted throughout its 16-day orbit of the planet. You'll find Titan due north of Saturn April 6 and 22 and due south April 14 and 30.
Saturn's other moons pose more of a challenge. Tethys, Dione, and Rhea all glow at 10th magnitude, but the last proves easiest to find because, of the three, it orbits farthest from the planet's glare. Expect to find it with a 3-inch scope. You'll need double that aperture to see Tethys and Dione clearly. Two-faced Iapetus lies east of Saturn this month, pointing its darker hemisphere in our direction. It glows around 12th magnitude, so you'll need an 8-inch scope to spot it.
[ 本帖最后由 卢平α 于 2006-4-15 12:17 PM 编辑 ] |
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