Doris Cook, age 12, of Philadelphia, Penna., for her question;
How can they predict eclipses?
Mankind has always been a stargazer. Even early man was impressed with the heavenly bodies ‑ the glorious sun, the changing moon, the stars and the visiting comets. History began when man made records of what he saw and some of his earliest records were made of what he saw in the sky. These records date back thousands of years,
The pageant of the heavenly bodies is usually slow, dramatic events, far apart. Modern astronomy depends on the old records to get an idea of the repeating patterns in the heavenly parade. For instance, the recurrence of Halley’s comet was tracked down through records dating back to 240 B.C. The recurring eclipses of the sun and the moon are also recorded thousands of years into the past.
The Chaldeans of ancient Babylon were the most studious of the early astronomers, Their country was the flat land around the Tigris and Euphrates rivers of Mesopotamia ‑ a fine place to view the unobstructed sky. These stargazers built tiered pyramids called zigurats to get an even better view of the heavens, Up the outside steps they climbed to their towers where they kept records of events in the skies.
The recurring eclipses of the sun and moon were‑ figured out by the Chaldeans before the dawn of history, Their studies showed that eclipses repeat themselves in cycles of 18 years and 11 and 1/3 days. They named such a cycle the saros, meaning repetition. The sun and moon still repeat their eclipses in this cycle and we still call it the saros. Each saros repeats the series of eclipses about 120 degrees west of the one before. After a third saros, the parade of eclipses returns to a little north or south of their first positions,
It is possible to predict the eclipses on the basis of the saros records dating back into the dim past. Modern astronomers can also predict them by figuring the position and orbits of the sun and moon. About 100 years ago, an Austrian astronomer put the records together and charted the eclipses from 120'7 B.C. -2151 A.D. into the future.
During each saros we can expect 29 lunar eclipses and 42 solar eclipses. Ten of the solar eclipses will be; total. The maximum number of eclipses in one year is seven, 3 lunar and 4 solar or 2 lunar and 5 solar. We had the full quota in 1917, 1935 and 1982.
The lunar eclipse is seen from a wide area of the earth. The splendid solar eclipse is seen from only alone a narrow path on the; earth. In this century, the New England area has been most blessed with the grand spectacle of the total solar eclipse. On August 31, 1933, this glorious sight was seen from a path beginning in the Atlantic, curving over New England, Canada, Hudson's Bay and northward. The great show was visible in New England on July 20, 1963.