 thumb|right|200px|a graphic depicting the new moon phase in astronomy, new moon is the first phase of the moon, when it orbits closest to the sun in the sky as seen from the earth. more precisely, it is the instant when the moon and the sun have the same ecliptical longitude.  the moon is not always visible at this time except when it is seen in silhouette during a solar eclipse or illuminated by earthshine. see the article on phases of the moon for further details. == determining new moons: an approximate formula == the time interval between new moons â a lunation â is variable. the mean time between new moons, the synodic month, is about 29.53 days. an approximate formula to compute the mean moments of new moon (conjunction between sun and moon) for successive months is: : d = 5.597661 + 29.5305888610 \times n + (102.026 \times 10^{-12})\times n^2 where n is an integer, starting with 0 for the first new moon in the year 2000, and that is incremented by 1 for each successive synodic month; and the result d is the number of days (and fractions) since 2000-01-01 00:00:00 reckoned in the time scale known as terrestrial time (tt) used in ephemerides. to obtain this moment expressed in universal time (ut, world clock time), add the result of following approximate correction to the result d obtained above: : -0.000739 - (235 \times 10^{-12})\times n^2 days periodic perturbations change the time of true conjunction from these mean values. for all new moons between 1601 and 2401, the maximum difference is 0.592 days = 14h13m in either direction. the duration of a lunation (i.e. the time from new moon to the next new moon) varies in this period between 29.272 and 29.833 days, i.e. â0.259d = 6h12m shorter, or +0.302d = 7h15m longer than average. this range is smaller than the difference between mean and true conjunction, because during one lunation the periodic terms cannot all change to their maximum opposite value. see the article on the full moon cycle for a fairly simple method to compute the moment of new moon more accurately. the long-term error of the formula is approximately: 1 cy2 seconds in tt, and 11 cy2 seconds in ut (cy is centuries since 2000; see section explanation of 
Phases_of_the_Moon