Friday, January 27, 2006

May 4, 2000

Today and tomorrow all seven classic planets will be bunched together in a rare conjunction. So why will you only be able to see three at most?

The catch is that the “classic planets” include the Sun. Therefore, when all of them are together, the others are close to the Sun in broad daylight and so cannot be seen.

At least not until the Sun is below the horizon, when the outermost of the grouping may straggle sufficiently to be visible just before they set in turn. Thus, a clear view of the westnorthwest in tomorrow’s evening twilight will reveal a thin crescent Moon (beside a bright star) and, to the lower right, faint red Mars. Binoculars are advised.

Why was the Sun originally counted among the planets? The Greek word from which our word “planet” is derived means wanderer, so the Sun, and also the Moon, were grouped with Mercury, Venus, Mars, Jupiter, and Saturn as the only naked-eye “stars” to move among the other, “fixed” stars.

After the fall and winter spectacle of converging planets, the night sky is peculiarly bare this month. So this is a good time to locate the three bright stars of spring.

Arc to Arcturus by extending in imagination the curve of the Big Dipper’s handle from its tip one Dipper-length in the direction away from the cup. Continue the arc a similar distance to Spica. The Moon crosses from right to left of Regulus on the 10th and 11th.

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