Astronomy Picture of the Day

Explanation: Tonight a bright full Moon will fade to red. Tonight's moon will be particularly bright because it is reaching its fully lit phase when it is relatively close to the Earth in its elliptical orbit. In fact, by some measures of size and brightness, tonight's full Moon is designated a supermoon, although perhaps the "super" is overstated because it will be only a few percent larger and brighter than the average full Moon. However, our Moon will fade to a dim red because it will also undergo a total lunar eclipse -- an episode when the Moon becomes completely engulfed in Earth's shadow. The faint red color results from blue sunlight being more strongly scattered away by the Earth's atmosphere. Tonight's moon can also be called a Harvest Moon as it is the full Moon that occurs closest to the September equinox, a time signaling crop harvest in Earth's northern hemisphere. Total eclipses of supermoons are relatively rare -- the last supermoon lunar eclipse was in 1982, and the next will be in 2033. Tonight's supermoon total eclipse will last over an hour and be best visible from eastern North America after sunset, South America in the middle of the night, and Western Europe before sunrise.