Gordon Uber wrote: > >The Microsoft Encarta 99 encyclopedia article on Solar Time contains the >following: > >"The difference in the length of the 24-hr day at different seasons of the >year >can amount to as much as 16 min." > >I think that they mean this to be a description of the equation of time, >but it >looks incorrect to me. > >They go on to use this to explain the need for mean time. > >Am I correct that this is an error? >
In my experience it is a common misconception by those new to dialling that solar days can be 16 minutes *longer* when they are simply *out of step* by 16 minutes. My analogy in explaining this is to say that the mean-time year is like a string of 365 beads which are all identical in size. By contrast a solar-year string has the same length and number of beads but the beads gradually increase and decrease in length so their mid-points (noon) only occasionally align. For an intended article on the subject I began a diagram to illustrate the difference in day length (average values) it is incomplete but one of the larger variations occurs around December 17th when the solar day is rougly 29 seconds shorter than the mean time day. If there are no howls of erudite protest at this statement I really must think about completeing the diagram and finishing the article. GIF on request. Tony Moss
