I blurted:
A diagram purporting to explain solar eclipses has two mysterious lines, apparently delimiting the penumbra, tangent to the sun, moon, and Earth! Even in the zero probability event that the three would align perfectly, this is wrong by a factor of 3,
referring to the tangent of half the angle between the lines. But it's closer to 1.8. Actually, its reciprocal.
and falsely implies that there is never a time when the whole sunlit hemisphere can see an at-least-partial eclipse.
This is backwards. The bogus lines show the penumbra all but covering one hemisphere. But the taper of the umbra from the lunar limb to essentially zero at the Earth is only slightly more gradual than the taper of the penumbra from the Earth back to the limb, which makes for a shadow slightly wider than twice the moon. rshad dmoon rsun dmoon dmoon rsun ----- = ---------- + ----- + 1 ~ 2.03 ~ ---------- + 1 rmoon dsun rmoon dsun dsun rmoon r:=radius, d:=distance from Earth. Picture: http://sunearth.gsfc.nasa.gov/eclipse/SEplot/SEplot2001/SE2006Mar29T.gif Sorry for the confission. --rwg PS, this lets me squeeze in one more math howler: "Find the area of a circle of radius 30cm. Round to the nearest tenth. Use pi = 3.14 ." It may not have been exactly 30, but they wanted five significant figures from a three digit value of pi! I forgot to ask if kids who used better values of pi got marked off.
"The weak force is the key to the power of the Sun."
I guess they don't want kids to know that solar power is really nuclear. PPS: I seem to have slipped that eclipse booboo past inventor/telescope maker Alan Adler, who recently remarked of the burgeoning field of cosmology: "Never have so many known so little about so much". I guess he never met the editorial board of Prentice Hall Science. Finally, apropos astronomy quotes is Rich's inspirational "'Tis better to shoot out a single street lamp than to curse the light pollution."