海角大神

Space photos of the day 08/04

08/04/2010 1:08 pm ET For billions of years, massive stars in our Milky Way Galaxy have lived spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation begins anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant was probably first seen in planet Earth's sky just over 300 years ago, although it took that light more than 10,000 years to reach us.