Lunar Distance from Speed

If you can figure out the lunar shadow speed, you are one step away from using it to estimate the lunar distance!

Step 1: Determine the surface speed of the shadow between two points along the path of totality.

Example: Newport, Oregon to Madras, Oregon is 232 km and the UT mid-point times differ by 0.0619 hours so the derived ground speed is 3746 km/hr. 

Step 2: Determine the angle along the surface of Earth between the observing point and McClellanville, South Carolina, q,  along the path of totality. This can be done using a piece of string and comparing the distance to the circumference of the earth along the same Great Circle, which equals 360 degrees. You can also use this formula:

Lunar Distance from Speed PDF download button

Thumbnail Image:Eclipse track map
Credit: Fred Espenak