Message text written by Frank Evans > .... but for navigators EoT has always been mean time minus apparent time. My British Admiralty Manual of Navigation, Volume 2, 1938 states simply: The equation of time is defined as the excess of mean time over apparent time.<
I have just looked up a few sources immediately available to me to try and demonstrate the different thinking on this topic and to see whether I was right to allege that it was a difference in thinking between navigators and astronomers. 1. Mayall & Mayall agree with you saying EoT = Mean Time - Apparent Time; and in their book 'Sundials' they quote from an American Ephemeris. They show the EoT running at +14 mins in February. 2. Waugh on the other hand tries to avoid allocating a + or - sign and treats the EoT as a number which is added or subtracted according to whether the dial is fast or slow. However arithmetically he adds the EoT to Mean time to get Apparent Time and thus shows EoT running at -14 mins in February. 3. My copy of Whitaker's Almanack in their Astronomy section observes that the Apparent Solar Day is shorter than average at the Equionoxes and larger than average at the solstices). It follows this convention to show EoT running at -14 mins in February. 4. As another check, the NASS Software Dialist's Companion shows EoT as running at -14 mins in February. 5. Then there is the web page of this man Powers (http://ourworld.compuserve.com/homepages/patrick_powers/homepage.htm) who also shows EoT at -14 mins in February - but you shouldn't believe him - he's biassed! Where does all that leave us I wonder? :-) It does look to me a bit as though it is a difference between navigators and astronomers. Patrick
