Hi Patrick: When I wrote my questions on sundial declinaton/date readings during a lunar eclipse, I thought that the experts on the List would have definite, clear-cut answers. I was wrong! Once again there seems to be disagreement. The good thing is that my assumptions can and will be easily proved or disproved by observation on the night of the eclipse. Let's see what happens!
Thanks for writing Patrick! >Message text written by John Carmichael > >>We have already discussed on the list the fact that moonlight should >indicate the correct time on a sundial during totality if corrected for EOT >and longitude and if its light is bright enough to cast a shadow. But what >happens to the declination readings on a sundial during a lunar eclipse? >I'm thinking that the shadow of the nodus should indicate a date which is >exactly six months from the date of the eclipse. In this case a sundial >with declination lines would show the date to be July 21. Is my theory >correct about this?< > >The declination of the moon is 'all over the place' in comparison with that >of the sun. I doubt (though do not know for sure) that it is any different >at the time of full moon. As a result I wouldn't expect a date reading to >be correct anyway at full moon let alone at one that coincides with an >eclipse.. Incidentally I think I am right to say that there are full moons >and full moons! In other words though the moon appears 'full' it is not >actually 100% illuminated - because of the declination effect. Even if, at >an eclipse, the moonlight is 100% illuminated the shadow given either side >of the actual eclipse would reflect the correct date rather than one 6 >months away... > >At totality, of course, in an eclipse (of the moon) there will not be >sufficient light from the moon to see anything on a dial.... > >Patrick > >
