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 axis of its elliptical orbit does not stay fixed, but slowly rotates, and the planet's point of nearest approach to the sun shifts each year. Calculations of classical Newtonian gravitation predict some shift, but not nearly so much as that actually observed. In desperation a French astronomer named Leverrier decided that the rest of the shift must be due to an unseen planet even closer to the sun than Mercury. Leverrier called it "Vulcan." He looked long and hard for it. Once a doctor peering through a telescope thought he saw Vulcan. He and Leverrier announced the discovery, were given banquets and medals for their find. But they never saw it again, nor did anyone else. Apparently "Vulcan" does not exist.

Then in 1915 Einstein produced his General Theory of Relativity, a beautiful theoretical concept but, after all, just a theory. Yet the Relativity mathematics was found to predict a shift of Mercury's orbit which was practically the same as the observed shift. This was the first observational prop for Relativity.* So Einstein may have felt a nostalgic glow last week, if anyone remembered to tell him that Mercury was transiting (passing directly between the sun and the earth).

At week's end, Mt. Wilson observers left the Naval Observatory in Washington to decide whether late Mercury meant the earth's time was 30 seconds fast. They decided it did not. Reason: both prediction and observation contained too large a margin of possible error. To disappointed laymen who had hoped for 30 extra seconds, it looked as though Mercury was just discrediting astronomers again.

*Others, established later: bending of starlight around the sun, stretching out of the wave length in light from heavy stars.

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