Science: Thirty Seconds

A 19th-Century stargazer once said that Mercury "seems to exist for no other reason than to throw discredit on astronomers." Last week the little planet (diameter 3,100 miles) was scheduled for a transit across the blazing face of the sun. From complicated formulas and tables, scientists had carefully determined the time. But when astronomers at Mt. Wilson's famed observatory shot the passage with motion-picture film synchronized with a clock, they found Mercury was 30 seconds late for its performance.

Transits of Mercury are a means of charting its queerly complicated orbit. The long...

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