# Measuring the circumference of the earth - revisited

I have done a bit of research on this topic already and the easiest way seems to be the experiment by Eratosthenes. We pick two locations on the same latitude (of which we know the distance) and then measure the length of the shadow of a vertical stick at solar noon to get two angles. We can then figure out the difference between these angles and plug it into the formula:

\begin{align} \frac{\text{angle}}{360°}&=\frac{\text{distance}}{\text{circumference of the earth}}\\[3mm] \text{circumference of the earth}&=\frac{360°}{\text{angle}}\times\text{distance}\\ \end{align}

Now I would like to do a similar experiment. My family has friends who live 1260km west (and a little south) from us. Is there a way for us take a measurement at the same time and calculate the circumference of the earth? Obviously the formula above does no longer apply since we never have the same solar noon.

• eratosthenes need to use the same latitude to correlate time with reports, you have a phone so you can do the same thing with different longitudes. – John Aug 7 '20 at 15:30