Bright Lunar Rays Project

Participating Organizations:

• The Association of Lunar & Planetary Observers
• The American Lunar Society
• The British Astronomical Association
• Britain’s Society for Popular Astronomy
• The Geological Lunar Research Group (Italy)
• The Italian Union of Amateur Astronomers
• (And other lunar observers regardless of affiliation)

Introduction

Conventional wisdom says that the worst time for lunar observing is when the sun is high in the lunar sky. It is at these times that shadows disappear and lunar features are difficult, if not impossible, to observe. But conventional wisdom does not always apply. When the sun is high in the lunar sky some of the Moon’s most fascinating features, the bright lunar rays, blaze into view. 

Rays appear to be distributed randomly across the lunar disc although those on the dark maria tend to show up most dramatically because of the contrast effect. Although often quite extensive, they have no appreciable height and are never seen to cast a shadow. They typically are uninterrupted by mountains, crater walls, or rilles but there is some observational evidence that this may not always be the case. 

Despite the early knowledge of their presence, bright lunar rays were once quite a mystery. Some early observers thought that they were cracks in the lunar crust that were later filled by dust or ice; others considered them to be salt deposits from extinct oceans. One of the more persistent theories was that they were volcanic in origin, similar to the features known as Pele’s Hair in Hawaii. We know now that they are the ejecta of meteoric and asteroidal impacts. 

Although they are some of the most easily visible features on the Moon, bright lunar rays are still among the most understudied. Therefore, the above mentioned organizations and dedicated independent observers have embarked upon a study of these beautiful and intriguing splash patterns.

For additional information see:
Project Objectives
List of rayed craters and other non-crater features
See the Resources section for links to websites related to lunar rays