Understanding Lunar Eclipse Colors: A Simulation of Atmospheric Effects

What is a Lunar Eclipse?

A lunar eclipse occurs when the Earth moves between the Sun and the Moon, casting its shadow on the Moon. Depending on whether only part of the Moon enters the umbra (the darkest part of the shadow) or if it's completely within, we observe partial or total lunar eclipses respectively.

The color of the Moon during an eclipse can vary from dark gray to brick red and everything in between.

Atmospheric Effects on Lunar Eclipses

During a lunar eclipse, sunlight passing through Earth's atmosphere is scattered by dust particles. This scattering preferentially removes shorter wavelengths (blue light) while allowing longer wavelengths (red and orange light) to reach the Moon.

The intensity of this effect depends on atmospheric conditions such as aerosol content, which can vary due to factors like volcanic eruptions or forest fires.

Danjon Scale

Developed by French astronomer André Danjon in 1927, the Danjon scale is a qualitative measure of how bright the Moon appears during an eclipse. Values range from 0 (very dark) to 4 (very bright).

The scale helps predict the color and brightness of the lunar surface during different types of eclipses.

Interactive Simulation

By adjusting sliders for Danjon level, umbra offset, and aerosol optical depth in our simulation, you can observe how these factors influence the eclipse’s appearance.

This tool allows you to explore the complex interplay of atmospheric conditions and their impact on lunar eclipse colors.

Frequently asked questions

Try it live

Everything above runs in your browser — open Lunar Eclipse Color Simulator (2D) and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.