Sunday, November 29, 2009
Take a look at Galileo's missed discovery
John Goss
John Goss is chairman of the Mid-East Region of the Astronomical League and a former president of the Roanoke Valley Astronomical Society.
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Blog
Our solar system contains eight major planets, with the outermost one, Neptune, lying nearly 3 billion miles from both us and the sun. Because of its great distance, Neptune receives only one-nine hundredth the amount of sunlight as our Earth, and, as a result, it is never visible to the unaided eye. It is so dim that astronomers didn't find it until 1846. Strangely though, Neptune was almost discovered well more than 200 years prior.
Galileo Galilei was the first person who scientifically studied the sky with a telescope. (In fact, 400 years ago this week, he drew his first detailed sketches of the moon's surface.) He already had been making careful telescopic observations of bright Jupiter and its four large moons for three years, when, on at least two separate occasions in December 1612 and January 1613, he made an unknowing discovery.
While examining the giant planet, he charted a much dimmer starlike object immediately to its east. Unfortunately, his small telescope was ill-suited to reveal the tiny planetary disk of this apparently unremarkable sight. If it had, Galileo would have discovered Neptune instead of just logging another dim, seemingly ordinary "star." Some historians believe that Galileo was completely oblivious to the true significance of his observation, yet others think he realized what he saw wasn't what it first seemed to be.
Galileo had unwittingly witnessed a very rare alignment of Jupiter and Neptune. A similar planetary circumstance happens throughout this December when Jupiter and Neptune align themselves again, although not as closely as they did in Galileo's time.
Today's binoculars are much better than Galileo's optical instruments. Illustrating that fact, binoculars can pick out the faint, pinpoint of Neptune over the next few weeks. The best dates for spying this distant world are Dec. 18 and 19, when there is no interfering moonlight washing out the sky. From a dark location, look in the southwest about 7 p.m. at bright Jupiter. Directly below and slightly to the right of the planet appear three stars situated in a line. Feeble Neptune lies above Jupiter's upper right at about the same distance that Jupiter is from the closest of those three stars.
Aren't binoculars amazing? For such a small instrument, they show so much. Each year, they can be used to enhance views of lunar features, of Jupiter and its four "Galilean" moons, of the crescent of Venus, of intriguing planetary arrangements, of star clusters hundreds to thousands of light-years away, and of nebulous stellar nurseries. Those are good reasons why all curious skywatchers should own a pair.
Binoculars require little storage space and they can be readied in a moment's notice. They are lightweight and give large fields of view. Many models can be mounted on a basic camera tripod for steadier views. All of this means that just about any family member can use them to explore the night sky. Best of all, their purchase need not break the budget, making them a great gift idea.
One activity where binoculars provide little use, however, is meteor watching. Meteors streaking across the sky simply move too quickly for binoculars to catch them.
Mid-December skies are the stage for the year's best, most convenient and most reliable meteor shower -- the Geminids. After 8 p.m. Dec. 13, more than 50 meteors per hour hopefully can be seen from a site away from city lights. Fortunately, moonlight is absent this year, giving hope for one of the best Geminid displays in recent years.
Dress warmly, prepare some hot cocoa, relax and let the meteors come to you.
