nebula NGC 3603, which is more than 20,000 light-years from Earth,
is the largest ionized hydrogen region in the Milky Way Galaxy.
The nebulas gas is ionized by intense ultraviolet radiation
from a huge cluster of newly formed hot, massive stars at its
core. This image mosaic by E. Kopan (Caltech IPAC) was constructed
from digital photographs taken by the 2MASS sky survey (see story,
p. 14) in three wavelengths of infrared light. This 1.1 MB image
and many others can be viewed at www.ipac.caltech.edu/2mass/gallery.