Expert: Jayendra Upadhye - 9/8/2006

Question
Is the earth's axis always in the same plane?
Thank you for any help.
Mary  

Answer
Hi Mary,
No!
The earth's axis describes a cylider tilted at 23.5 degrees to the axis passing thru the center of its orbital plane.

This happens because like a gyroscope, all through its orbit around the sun, the axis stays tilted at 23.5 degrees to the earth's orbital plane.

Take a pencil.
Place it's tip at a fixed angle on a flat sheet of paper.
describe a circle on that paper, holding the pencil at "that same" orientation all the time.

You will then be duplicating what the earth's axis does every year.

As with all things in science, this is "only largely true".
the small "false" part being that over a few 10s of 1000s of years, this orbital cylinder "gyrates".

The tilt itsef "precesses" describing a small circle, pointing at a new pole star all the time and completing the cycle known as the "precession of the equinoxes".

Indian and egyptian astronomers knew of this precession much before europeans learnt about it.

Egyptian priets had told Plato (who wrote about atlantis) that they had astronomical observation tables extending into the age before the flood (11,500 years ago) well upto 60,000 years ago!

Learn about the precession of the equinoxes on the web at wikipedia.

Hope that suffices.
Jayen