Astronomers last week were having learned fun with the transit of Mercurythe first in 13 years. When the small broiled planet (seared on one side, cold on the other) passes across the face of the sun, it always leaves a flurry of problems.
The transit itself was not spectacular, for planets are insignificant on the solar scale. Mercury looked like a grain of bird shot creeping across a pie. What interested the astronomers was the timing of Mercury's appearance. It never keeps appointments exactly, and they have learned a great deal by figuring out what makes it early or late for a...