# Estimating the Moon to Earth radius ratio with a smartphone, a telescope and an eclipse

## TL;DR

This study demonstrates how a smartphone, a telescope, and simple geometric analysis can accurately estimate the Moon to Earth radius ratio during a lunar eclipse, highlighting accessible astronomical measurement methods.

## Contribution

The paper introduces a straightforward, low-cost approach using smartphone technology and open-source software to determine celestial body ratios from eclipse images.

## Key findings

- Results closely match the known Moon-Earth radius ratio.
- Method proves effective with minimal equipment and quick analysis.
- Validates smartphone-based astronomy as an educational and research tool.

## Abstract

On January 20th, 2019, a total lunar eclipse was possible to be observed in Santiago, Chile. Using a smartphone attached to a telescope, photographs of the phenomenon were taken. With Earth's shadow on those images, and using textbook geometry, a simple open-source software and analytical procedures, we were allowed to calculate the ratio between the radii of the Moon and the Earth. The results are in very good agreement with the correct value for such ratio. This shows the strength of the smartphone technology to get powerful astronomical results in a very simple way and in a very short amount of time.