Equation of Time Approximation

[Thomas Klemm]

(02-19-2015 02:17 PM)Eddie W. Shore Wrote:  What causes the true solar day to not be constant?

From Wikipedia: Equation of time

Quote:The graph of the equation of time is closely approximated by the sum of two sine curves, one with a period of a year and one with a period of half a year. The curves reflect two astronomical effects, each causing a different non-uniformity in the apparent daily motion of the Sun relative to the stars:

• the obliquity of the ecliptic (the plane of the Earth's annual orbital motion around the Sun), which is inclined by about 23.44 degrees relative to the plane of the Earth's equator; and
• the eccentricity of the Earth's orbit around the Sun, which is about 0.0167.
  

Quote:The sun moves along the ecliptic and the speed about the ecliptic isn’t constant. Earth’s orbit around the sun is not a perfect (circle) but it is an elliptical orbit.

We'd encounter a variation of the solar day even when the orbit was a circle due to the obliquity of the ecliptic.

Cheers
Thomas