Alright, it isn't that simple, and I was closer to right the first time. Find out by what factor (f) the sun will be brighter, due to higher altitude, on the solstice, compared to the day of your experiment this week.
Calculate the sun's zenith angle at summer solstice noon, and find the cosine of that zenith angle. Multiply that cosine by f, and find the angle (A) with a cosine equal to that product. Tip the color-sample card so that its normal is that many degrees away from the sun. Do that by subtracting the absolute value of the sun's declination on the experiment day this week, from the complement of your latitude, to find the sun's altitude on the noon of the experiment. Add or subtract A from that altitude. Tip the color-sample card so that its north end is tipped up by the complement of that angle. In that way, the sunlight intensity on the color-sample card is what it will be on the horizontal dial at summer solstice noon. (unless I've made another error) Michael Ossipoff On Wed, Mar 1, 2017 at 10:27 PM, Michael Ossipoff <[email protected]> wrote: > What am I saying?? > > You don't need the formula for the sun's brightness at different altitudes. > > You just need to tip the color-sample card, from the horizontal, toward > the sun by an amount that's equal to the amount by which the > summer-solstice deciination (23.44 degrees?) will be greater than the solar > declination on the day of the experiment this week. > > That will give the color-sample card the same solar illumination that it > will have at solstice noon. > > On Tue, Feb 28, 2017 at 5:09 PM, Steve Lelievre < > [email protected]> wrote: > >> John, thanks for the clarification, and your patience with my questions. >> >> All, I'm off to buy some photographic mattes to do experiements with. >> This is all about having a horizontal dial face that is not too bright to >> view even in the summer midday sun - so I'll go quiet now and report back >> after the summer solstice. >> >> Steve >> >> >> >> On 2017-02-28 1:40 AM, John Lynes wrote: >> >> Hi Steve, >> I'm sorry I've confused you. >> >> ... >> >> The take-home conclusion is that there is no single ideal reflectance for >> the plate of a sundial. It varies with the sky illuminance. When Weber's >> Law prevails, a reflectance of about 60 per cent is likely to be a safe bet. >> >> >> >> --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> >> >
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