Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 July 12
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

Recycling Cassiopeia A
Credit: R. Fesen (Dartmouth) and J. Morse (CASA, U. Colorado), Hubble Heritage Team, NASA

Explanation: 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. In this gorgeous Hubble Space Telescope image of cooling filaments and knots in the Cas A remnant, light from specific elements has been color coded to help astronomers understand the recycling of our galaxy's star stuff. For instance, red regions are dominated by emission from sulfur atoms while blue shades correspond to oxygen. The area shown is about 10 light-years across.

Tomorrow's picture: weekend wonder

< | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
& Michigan Tech. U.