Dear Roger Baily, Arthur Carlson and Fred Sawyer, Thanks for all of your detailed answers to my inquiry as to whether one should correct sundial moonlight readings with the Equation of Time.
You all seem to be in agreement that to make an EXACT suntime/moontime correction requires some monstrous mathematics. As this information is going into my Owner's Manual, I really want to keep it simple for my average sundial customer (and for me!) In my manual I begin by explaining how the moon moves like the sun at night following roughly the same path. Then I point out that when there is a full moon the moon is opposite the sun on the horizon at sunrize and sunset. Everybody's seen this. Since the sun and the moon and the earth are in alignment during a full moon, the moon will act like the sun at night and the sundial becomes a moondial. I state the a good reading may be off by as much as 45 minutes because the moon's orbital plane is tilted 5 degrees away from the earth-sun plane. I provide an easy to read table with the classic 2 min./hr. (48min./day) lunar phase time correction. (my sundials are already longitude corrected). My customers are thrilled when the find out that they can use their sundials at night using the moon, even if it is 45 minutes off. I just thought that I could narrow down the error with the E.O.T. (they understand the E.O.T.) and still keeps it simple for the layman. I am still in doubt whether to use the E.O.T. Would you please reconsider your answers knowing that I'm trying to keep it simple for my sundial customers? Thanks again, John Carmichael p.s. I have noticed that right before, during, and after a partial or total eclipse of the moon that the sundial tells PERFECT time without using the E.O.T. I don't remember the dates so it might have happened on or near those times of the year when there is little or no E.O.T. correction.
