... Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. August 18, 1999 . Sun Block . ... Explanation: During a total solar eclipse, Earth's moon blocks the sun - almost exactly. While the sun is about 400 times wider than the moon, it is also about 400 times farther away and each appears to be half a degree or so in diameter. ... Tomorrow's picture: Light From The Dark Sun . ... About APOD > . ...