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
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
Well it's
1) How bright the dial face has to be for it to show a shadow when the sun
is as low as it can be at the sundial's mounting-location.
2) How un-bright does the dial need to be at noon on the summer solstice,
so that it won't be too bright to look at.
*As for #1*
, you can find that
