CHESHIRE
STAR WATCHby Jim Maynard
Star date: 05:18:97
Saturn, with its dazzling ring display, is in the pre-dawn sky this week, easy to find any time after about 3.30 pm. At that time, it will rise in the eastern sky, Jupiter, Uranus, and Neptune (the four "Jovian planets", named after Jupiter) are all also in this week's pre-dawn sky. The Sun is not rising until 5:15, and should not pose any problem for astronomical viewing of bright objects until 4:30, This will allow one hour of viewing of Saturn, and longer periods of viewing for the other planets we shall peruse this week. The Moon, just past full early in the week, will pose no problems for viewing Jupiter or Saturn, but could make finding Uranus or Neptune more difficult.
Saturn shines at magnitude 1.7 (as
bright as one of the brightest stars in the sky), and is the second largest
planet in our solar system. The density of Saturn is so low, that if one
could find a bathtub large enough, Saturn would float on water. The planet
is over 120,000 km (75,000 miles) across, slightly smaller than Jupiter.
See if you can see any of the moons of Saturn, as they circle their ways
around the ringed planet.
The largest moon of Saturn, Titan, is larger than the planet Mercury. Titan is covered by an atmosphere of hydrocarbons, which are the building blocks of life. Titan is so cold though, that it is unlikely life developed there.
The next planet on our agenda is the king of the planets, mighty Jupiter, It can be found in the south/southeast sky an hour before dawn. It shines brighter than any star, at magnitude -2.5. Look for this largest planet in our solar system about 23 degrees above the southeast horizon after Saturn rises. It will be far and away, the brightest object in the area, and is at the easternmost point of the constellation Capricorn. Jupiter also has a ring system, but the rings of Jupiter are 1,000 times dimmer than the rings of Saturn, and were not discovered until the year 1979. Jupiter is ten times the diameter of the Earth, and 1,000 of our planets could fit inside the king of the planets,
Out
next stop is the planet Uranus. This was the first planet found in recent
times, on March 13, 1781, by the astronomer William Herschel. He would go
on to develop the New General Catalog, in which nebulae are listed by their
NGC numbers. Uranus is also the first planet you need a telescope or binoculars
to see. Look for Uranus just 12 degrees west of Jupiter, laying 15 degrees
east of due south at 4:30. It will appear as a bluish/green disk (not a
point of light, like a star), and can be found in the middle of the constellation
of Capricorn. Uranus appears at magnitude 5.7, just barely not visible to
the naked eye, but an easy find with even the smallest set of binoculars
or a telescope.
The last of the Jovian planets visible to us now in the morning sky was discovered just 150 years ago, and is (until 1999) the most distant object in our solar system. This is the planet Neptune, Look for it 9 degrees west of Uranus. Binoculars or a telescope reveal this magnitude 7.9 object, like Uranus, to be a disk. Being magnitude 7.9 means Neptune is fifteen times too dim to see with the naked eye, even under the best conditions. Like Uranus, Neptune is a treat to find, knowing you are looking at an object which was never seen by a human being until just a few hundred years ago. Also like Uranus, you are looking at an object which nearly everyone has heard of, but very few people have seen. Unlike Uranus, however, Neptune shows a distinct baby blue color. If staying up late is more appealing to you than the thought of rising early, Neptune will be rising just after midnight in the southeastern sky.
Neptune is almost 50,000 km (about 30,000 miles) across, and lies 30 times further from the Sun than the Earth does. Keep in mind as you go out at night, that a clenched fist held at arms length appears about 10 degrees across. This will help you measure your way across the sky.
Clear skies, and good viewing.
James Maynard is head of the astronomy department at Earth Treasures in Keene, N.H.
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