# Why can I see the whole moon during various non-full-moon phases?

Here's an image that describes the phenomenon I'm asking about. The very thin sliver to the left is of course the surface of the moon as lighted by the sun. But the rest of the moon is also faintly lighted -- by what?

I'm guessing that some amount of "earthshine" -- sunlight reflected from the earth -- is the culprit here, but I've found no authoritative confirmation online. It would be great to have a link to a source that explains what's really going on.

• "I've found no authoritative confirmation online". Pity indeed. Wikipedia even lacks the "citation needed", though Leonarda da Vinci is mentioned; tt'll be interesting to find that reference. – user51 Dec 3 '14 at 15:38
• @Evert Yes, but it is probably one of those very understandable "what word should I google"-cases. It is difficult today to find information about any what's-its-name topic. EDIT: Ah, damn, he does mention the keyword "earthshine", ouch... – LocalFluff Dec 3 '14 at 15:47
• Perhaps NASA is a more credible source (with further links at the bottom): [The Da Vinci Glow ](science.nasa.gov/science-news/science-at-nasa/2005/…). – user51 Dec 3 '14 at 15:50
• Yes, it was basically a case of not knowing what to google. And yep, it turns out "earthshine" is a great keyword for getting google results on this (e.g., "moon illuminated by earthshine" reveals much) Funny, I didn't think to use the term "earthshine" until writing this question here -- another case where merely asking the question is enough to point at the answer. – TwoMice Dec 3 '14 at 22:15

A global and absolutely calibrated albedo can be determined by measuring the amount of sunlight reflected from the Earth and, in turn, back to the Earth from the dark portion of the face of the Moon (the earthshine' orashen light'). For more than a decade we have been measuring the Earth’s large-scale reflectance from BBSO. The observations are now done remotely utilizing our earthshine coronagraph under the small dome appearing to the right of the NST dome in the Figure 1. To get full coverage of the Earth, we have installed a carefully calibrated copy of the BBSO earthshine telescope in Tenerife