Astronomy Picture of the Day

Explanation: Tonight you might be able to see Halley's Comet again - or at least some pieces of it. It is widely thought that that the meteors from the Orionids meteor shower, which peaks tonight, are just small pieces of Halley's Comet falling to Earth. During each pass near the Sun, a comet will heat up and shed pieces of ice and rock from its nucleus. This debris continues to orbit the Sun until either evaporating or being swept up by some large solar-system body. A piece of comet debris striking the Moon creates a small crater, but a piece striking the Earth usually burns up in the atmosphere causing a brief, bright streak. Every year at this time the Earth crosses an old stream of bits from Halley's Comet causing the Orionids display, named from the constellation (Orion) from which the meteors appear to originate. The streak below centre in the above picture of the northern sky actually depicts a meteor from the Perseid meteor shower, a usually even more impressive display that peaks every year in mid-August.