Physically Based Real-Time Rendering of Eclipses

Abstract

We present a novel approach for simulating eclipses, incorporating effects of light scattering and refraction in the occluder's atmosphere. Our approach not only simulates the eclipse shadow, but also allows for watching the Sun being eclipsed by the occluder. The latter is a spectacular sight which has never been seen by human eyes: For an observer on the lunar surface, the atmosphere around Earth turns into a glowing red ring as sunlight is refracted around the planet. To simulate this, we add three key contributions: First, we extend the Bruneton atmosphere model to simulate refraction. This allows light rays to be bent into the shadow cone. Refraction also adds realism to the atmosphere as it deforms and displaces the Sun during sunrise and sunset. Second, we show how to precompute the eclipse shadow using this extended atmosphere model. Third, we show how to efficiently visualize the glowing atmosphere ring around the occluder. Our approach produces visually accurate results suited for scientific visualizations, science communication, and video games. It is not limited to the Earth-Moon system, but can also be used to simulate the shadow of Mars and potentially other bodies. We demonstrate the physical soundness of our approach by comparing the results to reference data. Because no data is available for eclipses beyond the Earth-Moon system, we predict how an eclipse on a Martian moon will look like. Our implementation is available under the terms of the MIT license.