PERIOD, in Astronomy, the time taken up by a star or planet in making a revolution round the sun; or the duration of its course till it return to the same part of its orbit. See PLANET.
The different periods and mean distances of the several planets are as follows:
| Days. | h. | ' | " | mean Dist. | |
|---|---|---|---|---|---|
| Herschel | 30737 | 18 | 1908352 | ||
| Saturn | 10739 | 1 | 51 | 11 | 954072 |
| Jupiter | 4332 | 14 | 27 | 10 | 520279 |
| Mars | 686 | 23 | 30 | 35 | 152369 |
| Earth | 365 | 6 | 9 | 12 | 100000 |
| Venus | 224 | 16 | 49 | 10 | 72333 |
| Mercury | 87 | 23 | 15 | 43 | 38710 |
There is a wonderful harmony between the distances of the planets from the sun, and their periods round him; the great law whereof is, that the squares of the periodical times of the primary planet, are to each other as the cubes of their distances from the sun: and likewise, the squares of the periodical times of the secondaries of any planet are to each other as the cubes of their distances from that primary. This harmony among the planets is one of the greatest confirmations of the Copernican hypothesis. See ASTRONOMY, p. 100 and 101.
For the periods of the moon, see MOON, ASTRONOMY Index.
The periods of several comets are now pretty well ascertained. See ASTRONOMY, No 306.