Time is based on the regular motions of celestial objects as seen from a specific body. 'Day' is defined as the time for a body to complete a rotation, but definitions vary as on what is the reference point for the rotation. A sidereal day is the rotation about the axis such that the distant stars appear in the same position in the sky. This takes 27.3 days. If referenced to the Sun, it takes 29.5 days. Since the Earth is also revolving around the Sun, it takes an extra 2.2 days for the Sun to appear in the same position in the sky.
The Earth also undergoes phases, as the Earth and Moon is always half illuminated by the Sun and their movements cause the phases. They are always in reverse, when it is Full Moon, it is New Earth, since they are opposites. With this, the synodic month on Earth would be in the same length of time with synodic "Moon month", which is at 29.5 days.
References:
Cain, F. (2008, October 21). How Long is a Day on the Moon? Retrieved April 16, 2014 from http://www.universetoday.com/20524/how-long-is-a-day-on-the-moon/#ixzz2z3AHNqKw
Changing Earth phases, seen from the Moon. (2008, June 21). Retrieved April 16, 2014 from http://earthsky.org/space/what-would-earth-look-like-from-the-moon
Timekeeping. (n.d.) Retrieved April 16, 2014 from http://csep10.phys.utk.edu/astr161/lect/time/timekeeping.htm
Prepared by Keanu Jershon Sarmiento
No comments:
Post a Comment