It is well known that two distant observers can estimate the distance to the moon using lunar parallax:

http://www.etwright.org/astro/moonpar.html

However, I propose a second way to confirm this is with two observers with high powered zoom (telescope or Nikon Coolpix).External Quote:Parallax is the apparent shift caused by viewing an object from two different vantage points. You can see it easily just by alternately blinking your left and right eye. Parallax is also evident in the apparent position of the Moon viewed from two distant points on the Earth, or from the same point six hours apart. Hipparchus, in the second century BC, derived a very good estimate of the distance to the Moon using lunar parallax.

Here is a shot taken from Alaska, alternated with one taken from Brisbane, Australia, within an hour of each other.

First, notice that the depth of the moon can be detected by observing that the craters on the edges only move about 3 pixels per frame, while the ones near the middle move about 14 pixels. Photoshop actually tells me 14.87 pixels if I use the ruler tool. This would indicate a depth to the moon.

Now, the diameter of the moon in this image is 1131 pixels, making its circumference 3553 pixels. Now, my thinking is that if you find a point near the center of the moon and note how many pixels it moves between the two shots, you can calculate the angle difference between two observers as:

Angle difference = pixel shift * 360° / pixel circumference. I think this should be essentially the parallax angle, and then using the parallax distance method, you should be able to estimate the distance to the moon. Let’s check.

The angle I calculate here is 1.506610506°, between two cities that are 6898mi apart. Using that distance as the arc length, we find that the chord length is 6058mi for the base line of our isosceles triangle. Using the parallax method, we find our estimated distance to the moon is:

Distance to moon = 1/2 base line distance / tan(1/2 parallax angle)

Distance to moon = 1/2 * 6068 mi / tan(0.7533052532° * ∏ / 180°)

Distance to moon = 230,369.98 mi

This is 3.57% away from the current estimated distance of 238,900 mi.

Using a second comparison from Santiago, Chile, to Maryland, I tried the technique again:

Circumference = 8507.43 px

Shift near middle of the moon = 28.07 px

Distance between observers = 5091 mi

Chord distance between observers = 4747 mi

Calculated parallax angle = 1.187808368°

Distance to moon = 228,970.71 mi

Error of 4.16%