StarWatch: Moravian College Astronomy
FEBRUARY STAR MAP |
- 232 FEBRUARY 4, 2001:
Venus Is Not For Lovers
- Venus, the goddess of love was one of the most celebrated deities of the ancient world. It is easy to see why. Just glance up in the southwest about 30 minutes after sunset, and youíll see against the paling sky a gleaming white diamond, truly one of the loveliest objects to grace our sky dome. During the month of February sheíll be the first "evening star," bright because she is currently the closest planet to the Earth, and because her cloud-covered surface reflects just over three quarters of the sunlight that falls upon it. As the third brightest astronomical object of the sky, following the sun and moon, it is easy to understand why Venus was held in such high regard. While her beauty might want to make you draw nearer, youíd be rudely awakened by the composition of her clouds, nearly pure sulfuric acid. Virtually all of the sunlight that penetrates the clouds never makes it to the surface. Venus would appear to any ground observer as a dull red world, not because of any minerals in her soil, but because her atmosphere would filter out all of the other colors. Then there is the atmosphere itself, nearly pure carbon dioxide, the waste product of our breathing. There is plenty of it on Venus too. Our own ocean of air presses upon us with nearly 15 pounds of force for every square inch of surface area, but on Venus youíd feel a force of over 1300 pounds per square inch. Try standing around with those kinds of oppressive forces pushing against you. The atmospheric composition and quantity of carbon dioxide precludes that surface temperatures all over Venus will be hot, about 900 degrees Fahrenheit. With Valentineís Day approaching next week, consider that beauty is only one small factor of a romance. Consider Venus.
- 233 FEBRUARY 11, 2001:
Jupiter On High
- High in the south around 7 p.m. is the fourth brightest object of the night, Jupiter. If you own a small telescope, you owe it to yourself to dust it off; and if you can find a space free of snow, point it at the giant of the solar system. Use your finder scope and your longest focal length eyepiece, the one with the largest number on it, to locate the planet. Then switch to a medium focal length eyepiece, like a 20mm, and behold wonders that even Galileo would have given his right arm to see as clearly. The first thing that youíll notice are Jupiterís attendants, four large and bright satellites, named the Galilean Moons after Galileo Galilee, the Italian astronomer and physicist who first turned the telescope to the heavens and discovered them in 1610. In order of increasing distance from Jupiter they are Io, Europa, Ganymede, and Callisto. They orbit Jupiter in periods of 1.77 days, 3.55 days, 7.15 days, and 16.69 days respectively, so they change positions from night to night. Io, Europa, and Ganymede are in resonant orbits. In other words, for every four Io orbits, Europa orbits Jupiter twice, and Ganymede orbits once. The resonance systematically causes the satellites to tug on each other from one direction while Jupiter tugs from the other. This generates heat causing Io to have active sulfur volcanism. Europa has a warm liquid water mantle beneath a very thin icy crust and ice volcanoes on its surface. Ganymede, which is tugged the least, shows past episodes of what looks like continental drift. If all four moons are visible, Ganymede and Callisto will appear to be brighter than the other two. Focus carefully, and look for dark linear bands across Jupiterís equator, regions of descending air in this liquid planetís extensive and turbulent atmosphere.
- 234 FEBRUARY 18, 2001:
Saturn's Rings Impress
- Donít put your telescope away just yet. If you gazed at Jupiter last week high in the early evening sky, then spy on that bright starlike object just below and to Jupiterís right. A mere 20-30 power will reveal that this again is no ordinary star, but rather what many skywatchers swear is the single most beautiful object in the heavens, the ringed planet, Saturn. Like the other eight planets and 91 moons of the solar system, Saturn gets its light from the sun, traveling a two billion mile round trip from the sun to Saturn and back to the Earth. Galileo with his rudimentary refractor never quite understood what those two appendages were hanging off each side of the planet. Today, even inexpensive telescopes at low magnifications will reveal the icy rings of this distant world. Jupiter, Uranus, and Neptune have rings composed of dust, or rock, or a combination of both. But Saturnís rings are chunks of ice. Since Saturnís axis is tiled by nearly 27 degrees to the plane of its orbit, we get various views of the rings. Right now, our vantage point provides us with a vista of the ringís underside. Increase the magnification of your scope to about 30-40 power per inch to see more. In other words, a refractor with a two-inch lens should easily be able to achieve magnifications of 60 to 80 power and still maintain a sharp image. With these higher powers you might notice Cassiniís Division, a 2610 mile gap in the rings where particles have been cleared away by the gravitational influences of Mimas, one of Saturnís 30 moons. If you notice a starlike object near Saturn, youíll undoubtedly be looking at Titan, Saturnís largest moon, larger than the planet Mercury. Titan will be closest to Saturn on Thursday.
- 235 FEBRUARY 25, 2001:
- There have been some incredible finds made recently with telescopes that are peering across billions of miles of space to image very small objects. Since 1997, an international team of astronomers has discovered five new moon orbiting Uranus, bringing its total to 21. These moons are all small, two of them about 60 miles in diameter, while the other three, discovered in July of 1999, are only about 12 miles in diameter. This same group decided to search for new satellites around Saturn. Since Saturn is closer to the Earth, the same imaging techniques yielded even smaller objects than those detected around Uranus. Their efforts reaped a bonanza of new discoveries late in 2000, twelve new moons for Saturn, catapulting the ice ringed world to the forefront of satellite heavyweights with 30 attendants. Not to be outdone, another team of astronomers was about to give Saturn a run for its satellites. The University of Hawaii group focused upon Jupiter and came up with 11 new moons by the close of 2000. Another Jovian moon had been discovered in 1999 by Spacewatch, a group of astronomers operating from the Lunar and Planetary Lab in Tucson. Jupiter now has 28 moons. All of the new Jovian satellites were less than 5 miles in diameter. The new satellites discovered around Jupiter, Saturn, and Uranus are called Irregulars. They orbit their parent planets at such great distances that their paths change with time. They move in directions which are opposite to the rotational motions of their parent planets. This indicates to astronomers that they were at some point independently orbiting the sun and then were captured. In total, the nine planets now have 91 satellites.