The “Da Vinci glow” is happening this week. If you look up at the sky this week, you may see a ghostly glow illuminating the whole moon. The Da Vinci glow is visible only when there's a crescent moon on the horizon at sunrise or sunset. What causes the effect? NASA explains it’s created by Earth, whose light can illuminate the night sky 50 times more brightly than that of a full moon. The famed artist and creator discovered the glow and wrote about some reasons as to why it happens. He was mostly wrong, though. You cansee the glow when a slim crescent moon is visible close to the horizon during the first or last few days of the moon's orbit. Tomorrow morning before sunrise is a good time and after sunset May 21 through 23.