This week (Feb. 19-26) the moon is in the crescent phase. If the weather is clear, you should be able to see earthlight - why does it always seem to be cloudy when you're looking for something like this? Anyway, that's a question for another time. The crescent moon is seen soon after sunset (when the moon is said to be young) or just before sunrise (when the moon is said to be old). At this time, most of the side of the moon that faces the Earth is dark, but the side of the Earth that faces the crescent moon is nearly fully lighted. The Earth and moon are opposite in phase. By this I mean that when the moon is full as viewed from Earth, the Earth as viewed from the moon is in the new phase (in full shadow), and so when rhe moon is new the Earth is in full sunlight. Sunlight which falls on the Earth and is relected toward the moon, is then reflected a second time back to Earth. Consequently, the moon is delicately lit by the Earth's reflected light. The expression "the old moon in the young moon's arms" refers to earthlight, the arms of the new moon being the "horns" of the crescent moon, which are almost touching when the moon is in the crescent phase. It's difficult to see earthlight when there is a quarter moon (half the moon is illuminated) because not only it is overwhelmed by the now larger portion of the moon's sunlit surface, but also because there is a thinner piece of the sunlit Earth shining in the skies of the moon.

An interesting thing about earthlight is that it can vary ever so slightly depending on the condition of the Earth's surface and atmosphere. For example, if much of North America and Eurasia are snow-covered or if there are an unusual number of storm systems so that the atmosphere is especally cloudy, then the earthlight may be a little brighter (it takes a keen eye to notice this, though).