A lunar day is the period of time it takes for the Earth's Moon to complete one full rotation on its axis with respect to the Sun. Equivalently, it is the time it takes the Moon to make one complete orbit around the Earth and come back to the same phase. It is marked from a new moon to the next new moon.
With respect to the stars, the Moon takes 27 Earth days, 7 hours and 43.2 minutes to complete its orbit; but since the Earth-Moon system advances around the Sun in the meantime, the Moon must travel further to get back to the same phase. On average, this synodic period lasts 29 days, 12 hours, 44 minutes and 3 seconds. This is an average figure, since the speed of the Earth-Moon system around the Sun varies slightly over a year, due to the eccentricity of the orbit. The Moon's own orbit also undergoes a number of periodic variations about its mean value, due to the gravitational perturbations of the Sun.
Read more about Lunar Day: Alternate Usage, Lunar Calendars
Famous quotes containing the words lunar and/or day:
“A bird half wakened in the lunar noon
Sang halfway through its little inborn tune.”
—Robert Frost (1874–1963)
“Until the day when, your endurance gone, in this world for you without arms, you catch up in yours the first mangy cur you meet, carry it for the time needed for it to love it and you it, then throw it away.”
—Samuel Beckett (1906–1989)