Lunar Periods
See also: Month| Name | Value (days) | Definition |
|---|---|---|
| sidereal month | 27.32166155 | with respect to the distant stars (13.36874634 passes per solar orbit) |
| synodic month | 29.53058886 | with respect to the Sun (phases of the Moon, 12.36874634 passes per solar orbit) |
| tropical month | 27.321582 | with respect to the vernal point (precesses in ~26,000 years) |
| anomalistic month | 27.554550 | with respect to the perigee (recesses in 3232.6054 days = 8.8504 years) |
| draconic (nodical) month | 27.212220815 | with respect to the ascending node (precesses in 6793.4765 days = 18.5996 years) |
There are several ways to measure how much time it takes the Moon to complete one orbit. The sidereal month is the time it takes to make one complete orbit with respect to the fixed stars, which is about 27.3 days. In contrast, the synodic month is the time it takes the Moon to reach the same phase, which takes about 29.5 days. The synodic period is longer than the sidereal period because the Earth–Moon system moves a finite distance in its orbit around the Sun during each sidereal month, and a longer time is required to achieve the same relative geometry. Other definitions for the duration of a lunar month include the time it takes to go from perigee to perigee (the anomalistic month), from ascending node to ascending node (the draconic month), and from two successive passes of the same ecliptic longitude (the tropical month). As a result of the slow precession of the lunar orbit, these latter three periods are only slightly different from the sidereal month. The average length of a calendric month (1⁄12 of a year) is about 30.4 days.
Read more about this topic: Orbit Of The Moon
Famous quotes containing the words lunar and/or periods:
“A bird half wakened in the lunar noon
Sang halfway through its little inborn tune.”
—Robert Frost (1874–1963)
“Compared to football, baseball is almost an Oriental game, minimizing individual stardom, requiring a wide range of aggressive and defensive skills, and filled with long periods of inaction and irresolution. It has no time limitations. Football, on the other hand, has immediate goals, resolution on every single play, and a lot of violence—itself a highlight. It has clearly distinguishable hierarchies: heroes and drones.”
—Jerry Mander, U.S. advertising executive, author. Four Arguments for the Elimination of Television, ch. 15, Morrow (1978)