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- 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
-