John Carmichael wrote: > My new Celestial Products moon calendar says that there will be a total > lunar eclipse at 4:41 UT on January 21 (the evening of Jan. 20th in North > America). > > 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?
Sounds right! The lunar declination should be near the negative of the solar, and your conjecture agrees with that. If the moon were *a little* off the ecliptic, the agreement with (solar +/- 6 months) might be off by significantly more than the delta angle would indicate, due to the different rate of change of declination in Summer vs. Winter. Ya think? > Those of you who have sundials with declination lines might want to check > this out during totality. I'm also curious if there will be enough > moonlight to even see a shadow. In dark-sky areas, the ambient light should track pretty well with the "inlunation", so, as far as the eye can adjust, it should work. If there is any skyglow from city lights, I'd expect that to wash out any trace of shadow at totality. Dave Bell Campbell, CA
