Spark image

The equation of time

This is the equation for the difference between mean and apparent solar time.
Solar time is not of continuous length. The length of a solar day varies due to:
(a) the fact that the Earth goes round the Sun in an ellipse and so moves at different speeds at different times of the year
(b) the Earth's axis is inclined at 23.5o to the plane of the orbit


Date Minutes   Date Minutes
January 1 -3.2   July 1 -3.5
January 16 -9.6   July 16 -5.9
February 1 -13.5   August 1 -6.3
February 16 -14.2   August 16 -4.4
March 1 -12.6   September 1 -0.2
March 16 -9.0   September 16 +4.8
April 1 -4.2   October 1 +10.0
April 16 -0.0   October 16 +14.2
May 1 +2.8   November 1 +16.3
May 16 +3.7   November 16 +15.3
June 1 +2.4   December 1 +11.3
June 16 -0.4   December 16 +4.8
 
 
 
© Keith Gibbs 2013