A

David

Darling

month

A month is a period of time connected with the motion of the Moon around Earth. The familiar calendar (or civil) month is an artificial unit consisting of a whole number of days. For astronomical purposes there are several other types of month.

 

Synodic month or lunar month
   The average interval from one new Moon to the next – 29.53059 days

 

Anomalistic month
   The interval in which the Moon passes from perigee to perigee – 27.55464 days

 

Sidereal month
   The interval in which the Moon passes from a fixed position with respect to the stars back to the
   same position – 27.32166 days

 

Draconic month or nodal month
   The interval between successive passages of the Moon through its ascending node

 

Tropical month
   The interval between successive passages of the Moon through the vernal equinox – a mean
   of 27.21222 days