"Crescent phase is where the starlight would be glancing off the edge of the planet toward our telescopes," says Williams, an associate professor of physics and astronomy at Penn State Erie. "That would be when the light is coming at the surface at a very steep angle, and the specular reflection would be the strongest and most intense."

Williams ran simulations of idealized, cloud-free planets with three types of surfaces: unfrozen land, snow and ice, and water. His goal was to see to what extent the presence of water would contribute to the light coming from a planet in another solar system.

Fascinating stuff!