Axis Angle to Ecliptic
Name: Keith J.
Date: June 11, 2004
A ten year-old asked me why the globe sits on the table
at an angle. Discussion of Earth's axis led to a question I couldn't
handle: What was observed way back when that led to determining the
Earth's cant to its orbit? Can we see it in our back yard?
I do not know specifically, but ancient astronomers noticed that
the plane of Earth's rotation (or perhaps in their way of thinking,
the movement of the Sun and other stars around the Earth) is not the
same as the plane of the solar system (you could see the Milky Way better
in those days without so many lights). The constellations did not
stay at the same angle above the horizon throughout the year, but
varied seasonally. It therefore became obvious to them that the Earth
tilted to the plane of the stars, although they may not have understood
why or that this is what causes our seasons.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
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Update: June 2012