Parallel Lines Never Meet – Unless You Bend One of Them!

   Ever wonder about the path our Moon takes relative to the ecliptic as it orbits the Sun with the Earth? I would ask that of my students and then follow up by asking if the Moon’s path is parallel with the Earth’s orbit, the ecliptic. Is it?
   Short answer – no the Moon’s orbital path is not parallel to the ecliptic. In fact the Moon is inclined about 5.14o from the ecliptic. This means that the Moon’s orbital path takes it above and then below the ecliptic in a repeating monthly pattern.

   At up to 3 times each month the Moon will cross the ecliptic moving south or north in what is called a node crossing – one ascending and the other descending. However as this graphic, of this months maximum northern most declination, shows the inclination angle is not the maximum amount the Moon will be from the ecliptic. Conceivably it could be as much as about 28.64o either north or south based on the Earth’s axial tilt of 23.5o plus the Moon’s inclination angle 5.14o (23.5 + 5.14 = 28.64).
   This month our Moon reaches a maximum northern most declination of 24.6o on October 9th

   Now that I have your attention (hopefully) here is a related question.
Does the Moon orbit the Earth or the Sun? *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.


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