ASK UNCLE SOL is a monthly feature in the club newsletter: The Smoky Mountain Astronomical Society Bulletin. All non-profit astronomy clubs are welcome to reprint it. We'd appreciate an acknowledgement. ASK UNCLE SOL ============= This month's question comes from little Debbie Doublet of Fraunhoffer, TN. Debbie asks, "Uncle Sol, What is an equatorial drive?" Uncle Sol answers: Debbie, as you probably know, before the rise of modern astronomy, most people believed the earth stood still. What you may not know is that at that time, it did. The rotation of the earth is due to a modern invention, the equatorial drive, which astronomers use to push the earth around under their telescopes. If it weren't for these drives pushing against the earth and turning it, in one hemisphere daytime would last six months, during which astronomers would not be able to observe their beloved nebulae. Even worse, in the other hemisphere amateurs would have six months of night, but no light by which to write checks for eyepieces and such. How does it work? If you have ever seen an illustration of an equatorial drive in action, you probably noticed that the telescope circles in one direction, while the earth is turned in the opposite direction: for every action there is an equal and opposite reaction. To the earthbound observer the scope appears to circle from east to west; actually, the drive is pushing the earth toward the east. Of course, one equatorial drive couldn't turn the earth fast enough to matter, but there are thousands and thousands of them out there chugging away every night. And to maximize the effect, astronomers line up their drives so they push the same way--around what they call the "polar axis." (The term derives from a tall pole that in pre-equatorial-drive days stood at Greenwich Observatory, directly under Polaris--which is why even today Polaris is sometimes called "the Pole Star.") You have probably noticed that many equatorial drives can be adjusted to run at different rates. This is to compensate for the number of star-gazers out. On an average night, the earth rotates at the proper speed, so objects stay in the equatorially-driven telescope's field of view. But if most astronomers are watching TV, the earth won't turn rapidly enough. Astronomers out observing notice the objects they want to see slipping out of view, so they increase the power to their drives to compensate. On the other hand, if there's nothing good on television a great many astronomers will be observing and the earth will spin too rapidly. So they decrease the power to their drives until the earth is spinning at the right rate. These corrections cause the breezes so common right after sunset. Precise fine-tuning of the earth's speed of rotation is achieved even though most of these hobbyists never get closer than 52 arc minutes to true celestial north. Their errors average out. At least the speed of rotation averages out; the axis on which the earth rotates has gone amuck. You see, once the earth began rotating, Polaris no longer remained over the pole. And over a long period of time, the scholarly consensus about the original location of the Greenwich pole has shifted several times. (Some archeoastronomers even claim that in 2000 BC the original pole stood in Thuban, in Egypt!) Since equatorial drives are aligned with whatever point the scholars say was originally directly above the pole, the earth now wobbles on its axis--a phenomenon known as "precession." Precession is encouraged by publishers of star atlases and celestial catalogues, as it has the beneficial effect of periodically requiring everyone to go out and buy new editions. This keeps several astronomers gainfully employed. The equatorial drive also explains why winter nights are longer. When it's winter here in the northern hemisphere, it's summer in the southern hemisphere, so southern hemisphere astronomers spend more time surfing and less time using their drives, and our days get longer. The same thing happens six months later, but then it's northerners who put in fewer hours, so the southern nights get longer. I think you'll agree that the equatorial drive is a wonderful example of a cooperative project from which all of us--even non-astronomers--benefit. ----------------------------------------------------------------------------- This month's question comes from little Debbie Draco of Dayton, TN. Debbie asks, "Uncle Sol, what's the difference between amateur astronomers and professional astronomers?" Uncle Sol answers: Debbie, the "amateur" in "amateur astronomer" comes from the Latin amare, to love: an amateur is a lover. Of course, no real lover would pack up 200 lbs. of gear and head for the countryside as night falls. The usage for stargazers arose in seventeenth century Italy, when the use of the telescope spread and many people (almost all of them men) started spending their nights outdoors with the stars. Their wives, annoyed at being left alone, took young gentlemen (amorosi) to comfort them. (Many of these amorosi were professionals.) The term was soon applied ironically to the betrayed husbands. When, in the Eighteenth Century, France beat Italy, 7-3, in the semi-finals, the astronomy championship passed into gallic hands, and "amateur" displaced "amoroso." Because their work was so demanding and required keeping odd hours, the professional amorosi were usually tired: "professional" comes from the Latin roots "pro," meaning like and "fessus," meaning tired -- a professional is like tired. For today's astronomers that's because these dudes spend all day wracking their brains with numbers and math and stuff like that. When the sun goes down they are so shot they flop into bed and are immediately asleep -- they're no lovers either. Since they sleep all night, many of them have little idea of what a star looks like in real life. The younger generation thinks galaxies look like CCD images, and are disappointed when little boxes don't show up through a telescope. ----------------------------------------------------------------------------- This month's question was sent in by little Debbie Aavso, of Finland, Kentucky. Debbie writes, "Dear Uncle Sol, what is Planck's Constant?" Uncle Sol answers: Debbie--Max Planck, the father of quantum mechanics, was a great physicist in the early part of the Twentieth Century. His fame was so great that he attracted physics groupies. One of them, a blonde, grew so attached to Max that she was always by his side, and so came to be nicknamed "Planck's Constant." The two were inseparable until one night, at a cocktail party, the famous astrophysicist Chandrasekhar, having consumed four martinis, playfully nibbled on Constant's roche lobe. Planck never spoke to either again. But for Max the evening wasn't a total loss, for he was soon to announce a discovery rivalling Planck's Constant: Chandrasekhar's limit is three martinis. ----------------------------------------------------------------------------- This month's question was sent in by little Debbie H. Doubleeye, of Excited State, TN. Debbie writes, "The other night I saw the Orion Nebula through a friend's telescope. What makes it so bright? Uncle Sol Answers: The clue was Hubble's realization that emission nebulae are always associated with powerful, hot, new stars. These O and B class stars are powerhouses at the blue and ultraviolet wavelengths. These short wavelengths pack a lot of energy; at the laid-back, languid, red end of the spectrum wavelengths are longer and less energetic. The long wave-lengths pass through clouds of hydrogen without ruffling any feathers, but the short, spunky ones, like little Jimmy Cagnies, smack into hydrogen atoms, knocking the electron loose. The result is unattached electrons running free, sometimes for months, and lonely, positively charged (ionized), hydrogen nuclei--H II, or in plain English, protons. Anyone can see this means trouble. When these lonely protons get a hold of an unattached electron, they won't let go. The captured electron is bewildered, and screeches, "Where am I?" There are several rooms in the proton's hotel, and the correct answer to the electron's question depends on which room it's landed in. But there is only one room the proton has booked for the electron--the room on the ground floor. If the electron has landed in some other room it gives off a quantum shriek, known as a photon, and jumps into the correct room. These shrieks are what we see when we look at emission nebulae. I hope this explanation has been helpful. --Sheldon Cohen