Total eclipse of the Moon: Repeating historical measurements

In this paper, we present our successful, low-cost experiment to reproduce historical measurements of longitudinal differences between places on Earth using timing measurements at the same lunar eclipse contact point from multiple sites. The observation is engaging, fun, and easy, but needs to be performed in collaboration with others, making it ideally suited for educational and outreach purposes. In an educational environment, it could be wonderfully combined with measuring the size of the Earth using Eratosthenes’s method, for which ample didactic material already exists, and with Aristotle’s ancient argument for the spherical Earth. This way, observing a lunar eclipse allows students to explore complementary ancient techniques for mapping our spherical planet. The method we reproduced here was suggested in Greek Antiquity, but actually performed only by Muslim scholars in West and South Asia from the 10th century CE onwards. In this paper, we also provide a detailed historical and technical background, along with our results from a recent eclipse, which can be used for prepare the lessons.