Hi John S. you wrote: >You are correct for the date but because the Earth's shadow is >approximately 4 times the moons diameter there can be quite a variation in >declination of the moon even during a total lunar eclipse. I haven't >checked the tables or programs for this one.
Isn't the apparent width of the moon about 1/2 deg? If the earth's diameter is about 4 times greater than the moon's, then the maximum possible angular variation would be 2 degrees. I'm guestimating that this would only throw a moondial off by a couple of minutes at the most. Even if you read the time just before or after totality when there is still enough moonlight to cast a shadow, I'd think that your reading would be almost correct. >> >>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. >> >During the total eclipse no. We'll see, won't we! I think a lot depends on how much local light pollution there is where you live. Do you live in or near a large city? >With the full moon on the Swensen sundial >I can really see the shadow but I can photograph it during the summer when >the moon is low in the sky (the Swensen dial is vertical)... >The exposure is about 15 >seconds at f 2.0 with 200 ASA film. >up even with a 30 second exposure. Of course you cant go much longer as the >moon moves approximately like the sun, 1 degree every 4 minutes. You have inspired me to photograph my sundials during the eclipse, but I think I will try higher speed film, maybe 400 or 600. Thanks for writing John C. > > >Professor John P.G.Shepherd >Physics Department >University of Wisconsin-River Falls >410 S. 3rd. St. >River Falls,WI 54022 > >Phone (715)-425-3196, eve. (715)-425-6203 >Fax (715)-425-0652 > > >
