Hi Gordon,
>"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?< It really is quite complicated. I think they must be referring to the Equation of Time which, of course is the difference between apparent solar time and mean time. This does vary from around 16m 23 secs (dial fast) to 14m 20s (dial slow). These are average values and there may be variations of something like 20 secs in any one year. The matter of the difference in the length of the 'day' is confused (in the English language) by whether we mean a 'day of daylight' or the full (24hr) day. Here they specifically say 24hr day and on that basis and measuring it as the time (using mean time) between successive local apparent noons, the variation is 24hrs plus up to 30 secs - with the longest (24hr) day being December 21st. The farthest it goes the other way is 24hrs less 21/22 secs on Sept 16th. There is another maximum and another minimum at around June 18th and Mar 28th respectively but then the excursion is not so great. The day with the longest amount of daylight is June 21st/22nd and there is a variation of something like 400 minutes or so (not accuracte that!) in the length of time between sunset and sunrise as one goes through the year. Patrick
