The terms synodical, sidereal, tropical, anomalistic, **nodical**, are applied respectively to these months, of which the lengths are as follow: - N This diagram is a key to some of the features reproduced in the photograph.

The anomalistic month is the mean time taken by the moon in passing from one perigee to the next; the sidereal month is the mean time in which the moon makes a circuit among the stars; the tropical month is the mean time in which the moon traverses 360° of longitude; the **nodical** or draconic month is the mean time taken by the moon in passing from one rising node to the next; the solar month is one-twelfth of a tropical year.

The lengths of the various months are: synodic = 29.53059 days; anomalistic = 2 7.554 60, sidereal = 27 32166, tropical = 27.32156, **nodical** = 27.21222, solar= 30.43685.