Lunacy...

The moon has 5 main kinds of month.:

The sidereal month.

  • Based on the moon's position in relation to the stars.
  • 27 days, 7 hours, 43 mins, 11.5 seconds. long.


A synodic month.

  • Which is the average period of moon's journey with respect to the sun as seen from earth.
  •  29 days, 12 hours, 44 mins, 2.9 seconds. 
  • The synodic month is used to calculate eclipse cycles.


The Draconitic month

  • The time it takes the moon to cross the ecliptic, ascending- drop down and cross (descending, and then cross the ecliptic once more, ascending. 
  • A Draconitic month is slightly shorter than the sidereal month, 27 days 5 hours,  5 mins, 35.8 seconds.
  • The plane of the moon's orbit precesses over a full circle in about 18.6 years.


An anomalistic month.

  • Because- the orbit of the moon around the earth is an ellipse not a circle.
  •  An anomalistic month is slightly longer than the other months. 
  • The position of the extreme point, when it is furthest away (the line of apsides: perigee and apogee) makes one complete circle (lunar precession) in about 9 years. 
  • The longer month has an average of 27 d 13 h 18 min 33.2 s. 
  • This affects the size of the moon as seen from earth, and when eclipses take place.


Finally, the tropical month

  • It is customary to specify positions of celestial bodies with respect to the vernal equinox. 
  • Because of precession, this point moves back slowly along the ecliptic. 
  • Therefore it takes the Moon less time to return to an ecliptic longitude of zero than to the same point amidst the fixed stars: 27.321582 days (27 d 7 h 43 min 4.7 s). 
  • This slightly shorter period is known as tropical month.




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