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The Straight Dope 

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What's the origin of the word "buck," meaning a dollar? --Anonymous, Denver, Colorado

As usual we have lots of speculation, no firm conclusions. Next time we start a language we gotta keep better notes. The leading theory at the moment is that buck comes from an old practice in poker. Evidently in the 19th century frontier card players were so thick they couldn't remember whose turn it was to deal from one hand to the next. So they placed a counter or token in front of the dealer du jour. This token was called a buck, since it was commonly a buck knife, whose handle was made of buck horn. When the time came for the dealer to surrender the job to someone new, he (you saw this coming) "passed the buck" to the new guy. Uh-huh.

A more plausible theory is that buck is short for buckskin, a common medium of exchange in trading with the Indians. As early as 1748 we have people writing, "Every cask of Whiskey shall be sold to you [Indians] for 5 Bucks." The transition to dollars seems only natural.

Curiously, "sawbuck," a ten-dollar bill, appears to be only indirectly related to buck. It got its name because some old ten-spots were denominated with Roman numeral Xs. The Xs looked like the X-shaped arms of the benches sawyers used to hold up logs for cutting. The benches, which were similar to today's sawhorses, were called sawbucks.

I have always thought it curious that planetary orbits are all in the same plane--in other words, that the solar system is essentially flat, rather than spherical like an electron cloud. This seems like a lot of organization. What gives? Are planetary moons and rings coplanar too? For that matter, does the plane of the solar system align with the plane of our galaxy, the Milky Way? Why? --Warren Nash, Dallas

Does seem kind of anal, doesn't it? But don't worry, this cosmic obsession with neatness extends only so far. All planetary orbits, except for those of Pluto and to a lesser extent Mercury, do lie in roughly the same plane, give or take two or three degrees. This plane is called the plane of the ecliptic.

At first thought, the idea of a flat solar system is surprising. After all, free-floating bodies tend to be spherical, not disc- shaped--e.g., soap bubbles, individual planets, etc. But on further contemplation we realize this only applies to nonrotating bodies. Anything that spins, e.g., the primordial hunk of glop that gave rise to the solar system, tends to form a disc perpendicular to the axis of rotation due to centrifugal force. It's only natural that when the planets coalesced, their orbits were in the same plane.

So why are there exceptions? Mercury is seven degrees out of alignment, which is no big deal, but Pluto is 17. Pluto's orbit is also much narrower than the others, so that sometimes (like now) it cuts inside the orbit of Neptune and becomes the eighth planet, not the ninth. Astronomers aren't sure why but suspect a cosmic accident. Some think Pluto was once a moon of Neptune that was thrown into a planetary orbit following a near-collision with some massive unknown planet.

Most asteroids orbit in the plane of the ecliptic, probably because they were formed out of the same disc that gave rise to the planets. But most moons aren't. Either they revolve around the equator of their host planet (most planetary equators, including earth's, are way out of line with the P. of E.), or else they have totally eccentric orbits, suggesting they may be captured asteroids.

Earth's moon is an exception. Its orbit is only about five degrees out of line with the ecliptic plane. Some see this as a sign that it isn't your garden-variety satellite, but rather is a planet unto itself, formed independently during the birth of the solar system. One current theory, in fact, is that the moon is what's left after a baby planet collided with us eons ago.

And that's about it for alignment. Saturn's rings rotate around its equator. Comets come in at any old angle. The solar system itself is 60 degrees out of line with the plane of the galaxy. Fine by me. I like my universes on the funky side.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.


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