The distance calculator will determine the separation distance between any two points projected over a meridian. We would like to thank Mr. Hector Covarrubias, who teaches at Colegio Madrid in Mexico City, for his help in improving this calculator.
Distance Calculator (for Internet Explorer)
Distance Calculator (for other browsers, including Firefox)
Enter the locations (latitude and longitude) of each pair of places, and the time and date when you took the measurements. Do this for each of the three pairs of places where your MY Partnership is making measurements.
You will need to enter the universal time (also known as GMT, Greenwich Meridian Time) at which this measurement took place. Please be aware of daylight savings time. You can use the following links to transform the reported local time into GMC:
When Eratosthenes used this method to find the size of Earth, he had several things going for him that made the calculation relatively easy. One of the two locations he used, the Egyptian town of Syene, is on the Tropic of Cancer... so the Sun was directly overhead there on the solstice, casting no shadow, and thus the angle of the gnomon's shadow was zero. The two locations Eratosthenes, Alexandria and Syene, have approximately the same longitude... Syene is almost due south of Alexandria. Finally, on the solstice, two places with the same longitude experience solar noon at the same time... further simplifying calculations.
In your case, the calculation is not quite so simple. To make up for that, we have provided you with the above distance calculator that will determine the "correct" distance between two places at which you are making sun angle measurements.
If you want to learn more about the reasons your calculation is more complex than the one Eratosthenes had to do, check out the links to videos below:
- Zenithal Circles and Earth's rotation on the June Solstice
- Zenithal Circles and Earth's rotation on the September Equino