Web edition: October 30, 2006
Print edition: November 4, 2006; Vol.170 #19 (p. 303)

Twisted logic?

I have a question concerning "The Sun's Halo in 3-D" (SN: 8/19/06, p. 120). It says, "As the sun rotates, its polar regions make a complete circle in about 34 days, compared with the 25 days required by its equator." I was wondering how it's possible to have two points on a rotating body take different amounts of time to make a complete revolution.

Mike Crawford
Snohomish, Wash.

The sun is a giant ball of gas, not a solid like a planet. Different points rotate at different rates, in a process called differential rotation.—R. Cowen

Dark secrets

I won't state that "dark matter" hasn't been discovered. However I disagree that empirical evidence for it is demonstrated in this collision ("Enlightened: Dark matter spotted after cosmic crash," SN: 8/26/06, p. 131). Other phenomena that could explain the images include excitation of preexisting gases or imaging artifacts. Nowhere in the article does it state that the mass of "dark matter" was actually observed passing unimpeded through the normal matter or other "dark matter."

Shawn Simpson
Orlando, Fla.

Shakespeare on the clock

There is a serious limitation to the "print clock" technique ("Mutant Maps," SN: 8/26/06, p. 136) that can probably be addressed. The method proposed holds good only for works with small print runs (such as expensive maps), where the damage to the printing surface in successive printings is minor in comparison to deterioration over time. Damage to the printing surface in the same run has already been studied in the case of Shakespeare's early folio texts, and can be significant. If researchers combine the data for two very different physical processes—deterioration owing to pressure on surfaces and repeated use and deterioration over time—the results will gain a great deal of accuracy.

Anthony Guneratne
Jacksonville, Fla.

Dust bust

I find it interesting that when we didn't find as much deuterium as we expected near the sun, we assumed it's hidden by dust ("Too Much Deuterium?" SN: 9/9/06, p. 172). But there didn't seem to be any real proof that it is indeed hidden by the dust. I am not convinced.

Eric Adams
Delray Beach, Fla.