Answer:
Check Newton's Rings:
d = height of air film
s = distance from center to ring being considered
R = radius of circle considered
The approximate formula is:
d = s^2 / (2 R) or s = (2 R d)^1/2
If we just use 4000 mi for R and 1/4 mi for d the height
we get s = (2 * 4000 * 1/4)^1/2 = 2000^1/2 mi = 45 mi
