Question No.  2275 :
Why does the Moon rise approximately one hour later each evening? Thank you.

Because the Earth rotates daily, the apparent rotation of the celestial sphere carries the Moon 15 degrees per hour westward. Thus the Moon rises in the east and sets in the west, like most other celestial bodies. As the Moon revolves around the Earth, its position in the sky changes with respect to the stars. In one sidereal month (27.3 days), the Moon returns to the starting point on its celestial sphere, having traced out a great circle in the sky. Hence the Moon moves about 13 degrees ( i.e. 360 degrees divided by 27.3) to the east every day with respect to the stars. Each night, as a result, the Moon will rise (and set) later and later; on the average by 50 minutes per day. (The time required for the Moon to complete a full cycle of phases, one synodic month, is a little longer - about 29.5 days. This synodic month is a little longer than the sidereal month for the same reason that a solar day is slightly longer than a sidereal day. Because of the motion of the Earth around the Sun, the Moon must complete slightly more than one full revolution to return to the same phase in its orbit.) Question Asked By:

Name: Mark Schiffner

Age Group: 30 and above

Occupation Type: Others

Education Level: Graduate