[EMAIL PROTECTED] wrote: > [EMAIL PROTECTED] wrote: >> > The reason for the variation in the length of the days (measure by > solar time) is due to two factors, and they're both related to the > fact that a day isn't just one revolution of the earth, it also > includes a small component representing the amount extra that the > earth has to turn each day to face the sun, because it's travelled a > little bit further around its orbit so the sun isn't in the same > apparent position any more: > > (1) the earth's orbit is an ellipse, and its speed around the orbit > varies with its distance from the sun as described in Keplers laws. > > (2) The earth's axis is tilted relative to its orbit. This means that > the sun's apparent movement against the background stars isn't a > circle, but climbs and falls at different times of year. When it's > climbing and falling, its speed of movement when extrapolated down to > the horizon is slightly slower than when its travelling horizontally > at its peak and trough. I think. > > There are websites that explain it better. Try searching on > 'analemma'....
It also screws up sundials as well (asumning we get any sun...) IIRC they are about 20 mins fast in summer and 20 mins slow in winter - only correct at March 21 and Sept 21. Ron Jones Process Safety & Development Specialist Don't repeat history, unreported chemical lab/plant near misses at http://www.crhf.org.uk Only two things are certain: The universe and human stupidity; and I'm not certain about the universe. ~ Albert Einstein
