Click the cartoon to go to XKCD. The hover tag is worthwhile, as usual.
Daily Archives: April 10, 2009
You Killed My Mascot!
Sometimes I think my students lack a sense of humor
It turns out that thousands of years before the falls retreated to their current position, a big chunk of that upper layer of rock fell on top of a giant beaver who was unfortunate enough to be building a dam in the vicinity. (When they say giant, they aren’t kidding. Those suckers are apparently about 300 pounds full grown. One of my students, who is a football player, said that it’s too bad they’re extinct as they might be useful on the football team.) The skeleton of the beaver, which is on display at the Science Museum of Minnesota, was radiocarbon dated to determine how long ago it died. The students use this age to determine the overall rate of retreat for the falls.
I’m not sure if the giant beaver is the actual mascot of Oregon State, but it should be. Some of the iterations they used when I was there looked too much like Chip ‘n Dale
Everybody's Doing It
C’mon baby, do the polar motion!
I mentioned that I printed out several posters for some colleagues for our Open House. Since they were displayed to the public and not copyrightable (work of the US government), I feel free to share.
Earth rotates about an axis, but this axis does not always coincide with the (geographic) North Pole.
The plot shows the location of Earth’s spin axis over the past few years. The center of the spiral is not at the geographic North Pole: it’s about 9 meters (~ 27 feet) away.
Why: early-20th-century geodesists adopted the rotation axis position of 1900 as the geographic North Pole; the rotation (spin) axis has migrated to its current position since then.
Knowing the true location of Earth’s spin axis is important when using star locations for navigation and timing, because the true spin axis determines where the stars will appear in the sky (as opposed to where one would expect them to be, were the spin axis at the North Pole).
“Polar motion” – the difference between Earth’s true spin axis and geographic north – is computed by combining measurements from radio astronomy, GPS and satellite ranging.