Albedo
A planet's albedo is the proportion of the light it receives that is reflected back into space. The album title refers to the average albedo value of the planet Earth as it was in 1976. From the explanation on the back of the LP cover : "The reflecting power of a planet or other non-luminous body. A perfect reflector would have an Albedo of 100%. The Earth's Albedo is 39%, or 0.39".
Due to a variety of solar, atmospheric, electromagnetic, seasonal, and pollution issues, Earth's albedo value is in constant flux. See 'Sources', below, for data pertaining to the issue.
Read more about this topic: Albedo 0.39