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Frame of Reference

This is geocentric with tex2html_wrap_inline196 (unit vector) along the earth's axis of rotation. The frame rotates uniformly about tex2html_wrap_inline196 at one revolution per year (approximately 365.25 days) such that tex2html_wrap_inline200 points towards the sun at each equinox and the X-Z plane includes the sun at solstices. Let us start the year at the winter solstice.