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Copernicus recategorized the 7 ancient planets by recognizing that the Sun is the center of the Solar System, and Earth is simply a planet orbiting the Sun. Since then, the term "planet" has only told how an object moves: it orbits around the Sun. The term does not tell about its physical nature, despite the impression you got in grade school.
William Herschel discovered Uranus in 1781, calling it (for want of a better term) a "comet"; by the following year the world's astronomers had agreed, to their surprise, that it is a planet. When Ceres, Pallas, Juno, and Vesta were discovered between Mars and Jupiter, 1801-7, they were called planets, too - textbooks of the 1830s describe "the 11 planets". When Neptune and more little planets were discovered in the mid-1840s, the little ones got demoted to "minor planets" or "asteroids", reducing the number of "planets" to 8.
Each of the 9 objects currently called "planets" (based solely on how they move) can now be associated physically with objects listed another way:
- Gas giants are akin to brown dwarves, "wanna-be stars" made of the same gasses as stars, but not containing enough of them to spark the stable fusion that marks true stardom.
- Rocky planets are akin to the 7 big moons, all of which are more massive than Pluto. The term "moon" itself merely means "it orbits around a planet"; the word tells nothing about the objects' physical natures. (Many asteroids have moons, too.) Certain little moons like Phoebe and Nereid are probably captured icy objects, and Phobos and Deimos might be, too. Moons turn out to be largely rocky but most also have ices. The motion label "moon" can co-exist with the physical label "icy".
"Comet"
The "comet" category earned its label by looking "fuzzy" or "hairy"; if an object looked fuzzy, it was a comet. The same Greek root word operates in "coma" and "comb". Nobody knew how comets were physically constructed till a fleet of spacecraft visited Halley's Comet in 1986. The European Space Agency programmed its Giotto probe to point at the brightest thing in view because, as everybody "knew" from Fred Whipple's 1950 theory, the nucleus was a "dirty snowball" and therefore must be white. That remained conventional wisdom till the moment the images came back. The brightest thing in view was not the nucleus, it was gas jetting off the nucleus. The nucleus itself was black, not white. Surprise! A comet nucleus is very dirty.
(That cleared up a little problem from the spectacular 1858 passage of Comet Donati. Detailed drawings showed a black spot at its nucleus. At the time, they called that the "shadow of the nucleus", thinking the nucleus should be bright. We now understand that the black spot was not the shadow of the nucleus, but the nucleus itself.)
The fuzzy appearance of comets comes from gases and dust liberated when the Sun heats up the approaching nucleus. Now, we pay attention to the long-lived nucleus as well as to the fleeting vapors; to the dark object as well as the white veil; and to the physical components, a hodge-podge of ices, crumbly tarry goop, and rock bits. We now regard the nucleus as an "object", and the gaudy tails are more of a "temporary phenomenon when close to the Sun". So research has outmoded the old cultural description that comets "look fuzzy".
Pluto
Pluto was labeled a "planet" for historical reasons, not physical reasons.
Pluto was discovered in 1930 by Clyde Tombaugh, a wonderful person, at Lowell Observatory. He was searching for a planet beyond Neptune and found this object there. Since he found this object where he was seeking a planet, he called it a planet. Nobody knew Pluto's physical character till the 1970s and 1980s.
The planethood dispute is sparked by realizing that Pluto is so icy that resembles a comet - indeed, there is no known difference. Its orbit is so elliptical and tilted that some astronomers call it more cometary than planetary. Even its atmosphere is indistinguishable from a comet's coma. If astronomers had known, in 1930, what Pluto is physically like, and what comets are physically like, they would have called Pluto "a heck of a big comet".
"Planet" is just a motion label. Pluto could be "a comet-like icy body that is so big it is a planet" or "a planet that is physically like a giant comet nucleus".
DebunkWas the Loch Ness Monster an Aurora?
Astronomical effects influence a lot of fields. But specialists in those studies don't always know enough astronomy to recognize what's really happening. Here's an example on a famous topic that no one would expect to have an astronomical dimension.
The highly-publicized hunt for "Nessie", the Loch Ness Monster, interests scientists and skeptics as well as the "crypto-zoologists" who hope that, in addition to the millions of small species that (naturalists assure us) remain to be cataloged, there may also be some unusually big ones. Discovering big new animals wouldn't violate anything scientific, and it would definitely be cool.
Nessie's setting is well known. In Scotland there lies a long, narrow, deep lake, Loch Ness, famous for its opaque waters. Sporadic reports from locals and tourists suggest that a large aquatic animal lives there, only rarely surfacing. A few ambiguous photographs and a lot of folklore support Nessie. The local hotels hope the hype continues to draw even more tourists than the pleasant landscapes and local culture earn on their own. Similar phenomena include "Champ" in Lake Champlain, Vermont, and "Ogopogo" in Okanagan Lake, British Columbia.
Just what the creatures might be, if real, remains to be demonstrated. I often heard plesiosaurs suggested, though these large marine reptiles are thought to have met extinction at the same time as dinosaurs, the end of the Cretaceous period, 65 million years ago. No plesiosaur fossils have been found in any later rocks.
"Remember the coelacanth!", the advocates remind us. These large primitive fish were also thought to be extinct, and now we have specimens of 2 species caught live - one species near the Comoro Islands and South Africa in the Indian Ocean, and the other in Indonesia. But the main reason to suspect a plesiosaur was its similarity to the "surgeon's photo", now admitted to have been a 1930s hoax.
A number of expeditions have sought Nessie, using more or less technological devices, and techniques of varying sophistication and likelihood of success. The one that produced the strangest result - often cited as the best scientific evidence for Nessie - was conducted in the summer of 1972. A sonar transducer (which converts sounds into electrical signals) was submerged 35 feet in the dark waters, connected by a long wire to analytical equipment aboard a boat. The transducer's signal traveled along that wire to amplifying electronics aboard the ship. If Nessie swam by the sonar detector, it would say so, even if Nessie stayed out of sight of the nearby submerged cameras. That is objective and neutral: no large signals means no large object, no Nessie; large signals can mean Nessie is there.
An hour after midnight on August 9, 1972, the sonar produced the peculiar strip-chart recording which is most often cited as showing the Loch Ness Monster. Though published1, this strip-chart is so different from conventional sonar output that even pro-Nessie studies quote the opinions of authorities, and several of those hedge2. Items by Rikki Razdan and Alan Kielar in the Skeptical Inquirer have disputed the positioning of the transducer (free-swinging or stationary), the stimulus for looking there and then (a dowser's signal), and the interpretation of the strip-chart. The matter remains controversial.
Despite the decades since then, I remember vividly where I was and what I was doing that week. I was in Springfield, Vermont, at the most famous astronomical convention in America. "Stellafane" is intended for people who make telescopes, but every year thousands who don't grind their own flock there too. I was attending my first Stellafane that very weekend. The sky was clear and dark. The Milky Way shone prominently. But everybody's attention was on something else. Brilliant green aurora - "Northern Lights" - flitted all around the sky. This was the finest display I have ever seen - the longest, the brightest, the most detailed and the fastest flickering, covering the most sky, right down to the south horizon.
In fact, this was one of the strongest auroras in decades, occasioned by one of the strongest solar flare outbursts recorded to that time. The Sun had just spat out a lot of charged particles, and they whipped Earth's magnetic field around, causing quite a lot of havoc. The storm induced electric currents in long wires, with many reports of damaging voltage and amperage variations. There were surges in the Canadian electric power grid; a big transformer exploded; short-wave radio communications were gravely disrupted; and sensitive electronic equipment was subjected to surges and flutters and spikes of current. Sky & Telescope magazine covered the event with no less than 5 articles, and J. A. McKinnon compiled a whole monograph on the event.
Much of Europe reported aurora and other electromagnetic phenomena from this solar storm. Loch Ness lies closer to the zone of greatest auroral intensity, the "auroral oval", than most of Europe.
The peculiar sonar reading occurred at just the time of the second-greatest peak of magnetic intensity. But the Loch Ness investigators didn't report the aurora. Most likely it was cloudy there, as it is about 90% of the time. Even had it been clear, their attention would have been focused down toward the waters, and it would be entirely understandable if they didn't notice diffuse phenomena occurring behind them and apparently unrelated to their interests. They did, however, note that "the hair went up on the backs of their necks" - an effect well-known in electrical demonstrations - though they interpreted that as "primitive instincts" that "there was something ominous in the loch that night"3.
One sensitive electronic instrument, using a long wire, did give a peculiar reading just when an exceptionally strong gust of solar wind swept by Earth, just when hair rose on their necks. The least-strange interpretation is that this sonar recorded the magnetic storm, rather than the Loch Ness Monster. This might explain why the reading from the Loch Ness equipment is so strange that it requires expert interpretations, and why those say different things.
If so, the Loch Ness investigators may deserve a more charitable treatment than some skeptics have given them. They reported what their instrument told them, and that instrument gave a reading that is possible to interpret as data confirming an unusually large object or creature. The hair-raising clue alone was too little to pick up on. The aurora was probably hidden by clouds, and even if visible would not likely attract their attention, let alone their suspicion. And while atmospheric scientists and astronomers would connect the aurora to the strangeness of signals riding long wires, few other scientists would suspect their instruments of telling them anything beside what they're designed to tell.
Absence of evidence is not evidence of absence, so you can still root for Nessie. But the scientific evidence (with the sonar reading resulting from aurora, and the "surgeon's photo" an admitted hoax) is very meager.
Everything people deal with is embedded in a cosmic setting. The better people understand the cosmos, the better they can deal with it.
Notes
- Scott and Rines, 1975, p 466; Rines et al., 1976, p 31.
- Rines et al., 1976, pp 36-7.
- Rines et al., 1976, p 30.
References
- Klein, M., and C. Finkelstein, Technology Review, vol. 79, no. 2, 1976, p. 3.
- McKinnon, J[ohn] A[ngus], August 1972 Solar Activity and Related Geophysical Effects, Technical Memorandum ERL SEL-22, Space Environment Laboratory, Environmental Research Laboratories, National Oceanic and Atmospheric Administration, Boulder, Colorado, December 1972.
- Razdan, Rikki, and Alan Kielar, "Sonar and Photographic Searches for the Loch Ness Monster: A Reassessment", Skeptical Inquirer, vol. 9, no. 2, Winter 1984-5, pp. 147-158.
- -, "Loch Ness Reanalysis: Authors Reply", Skeptical Inquirer, vol. 9, no. 4, Summer 1985, pp. 387-9.
- Rines, Robert H., Harold E. Edgerton, Charles W. Wickoff, and Martin Klein, "Search for the Loch Ness Monster", Technology Review, vol. 78, no. 5, March-April 1976, pp. 25-40.
- Rines, Robert, et al., "Loch Ness Reanalysis: Rines Responds", Skeptical Inquirer, vol. 9, no. 4, Summer 1985, pp. 382-6.
- Scott, Sir Peter, and Robert Rines, "Naming the Loch Ness monster", Nature, vol. 258, 11 December 1975, pp. 466-8.
Sky & Telescope magazine articles on this magnetic storm appear in October 1972, pp. 214, 226, and 237; November 1972, p. 333; and February 1973, p. 130.
The Dim, the Weakand the Ugly
How does a researcher select what to research? How does an editor select what to publish?
In both processes, the humans involved are often attracted to bright and beautiful objects. For the researcher, "bright" means plenty of light is available, making it practical to take detailed photographs and spectra. For the picture-editor who has to select some items and leave out others, bright and beautiful objects beat dim and ugly ones.
This means that the results reported in textbooks, the press and research journals are not a fair sample.
Red Dwarf Stars
The most abundant type of star seems to be the red dwarf. It's certainly the most abundant type within 25 light years. The very closest star to the Sun, Proxima Centauri, is a red dwarf - but so dim that you need a telescope to see it. Even the brightest red dwarf is too dim to see without binoculars. Since red dwarves are very difficult to recognize, hardly any are known.
For all their abundance, they aren't studied by very many researchers. Compared to other types of stars, they're dimmer, so there is less light to study. They are generally thought to not do much, other than sporadic unpredictable flares, so there is little of interest to attract researchers.
If red dwarves were studied as intently as, say white dwarves or red giants, would more interesting things would be discovered about them?
Thin Nebulæ
Bright, thick nebulæ get lots of attention. For active nests of stars, for beautiful twists and knots, they look great. There are lots of thinner, dimmer nebulæ cataloged, but only a few observers track them down. Mostly, thin, dim nebulæ get ignored.
If thin nebulæ were studied as much as thick ones, would more interesting things be discovered about them?
Dwarf Elliptical Galaxies
In nearby clusters of galaxies, the most abundant galaxy type is the dwarf elliptical. To see even the brightest requires a significant telescope. Beyond 50,000,000 light years, dwarf ellipticals are very difficult to recognize. Because they are small and faint, not many are known.
For all their abundance, they aren't studied by very many researchers. Compared to other types of galaxies, they're dimmer, so there is less light to study. They are generally thought to not do much, having little nebulosity and no big powerful stars, so there is little of interest to attract researchers.
If dwarf ellipticals were studied as intently as, say, spirals or giant ellipticals, would more interesting things would be discovered about them?
With Galaxies, as With People,
Pictures Show the Most Attractive,
Not the Most Typical
People who select illustrations for books, slide sets, and other media naturally tend to pick the most attractive examples. This leads to some important misunderstandings. People looking at the examples tend to think they're typical, when actually they are not.
"Spiral" galaxies, which physically are disc galaxies, are prettiest to most humans. Therefore, the prettiest spirals show up in books and slide sets a lot more than others do. Ragged and less-symmetrical spirals, and elliptical and irregular galaxies, hardly ever get selected, even though ellipticals are very abundant.
Most textbooks include a photo of the beautiful galaxy M 51, the "Whirlpool". This is the galaxy with the most obvious spiral appearance; smaller telescopes (perhaps 35 cm) will reveal its arms than any other galaxy's. Many books call M 51 "a typical spiral galaxy". It is actually one of the least typical! Very few disc galaxies have continuous arms that can be traced so far around. Hardly any other bright galaxy has such vivid arms. Enjoy the beautiful view, but don't swallow the claim that it is "typical". It isn't, which is why so many books include it. More typical galaxies don't look as handsome. Editors select the nicest-looking pictures, therefore making the selections anything but "typical".
Barred spirals, too, rarely look like their "typical" case, NGC 1300. That one, again, looks prettier and cleaner than most. That's a good reason to publish its picture, but it's wrong-headed to call it "typical".
Much the same applies to planetary nebulæ, pre-stellar nebulæ, and surface features on planets. Editors (and often researchers) select the brightest and most attractive ones. Dimmer and less-attractive examples may be more typical, but they're less-often studied and shown.
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