Niels Bohr 
Teapot-shaped Sagittarius tips above the southwestern horizon on early autumn evenings. Under dark skies, the Milky Way rises from its spout like steam. For those with a telescope, the edges of the steam offer some amazing sights, such as the Trifid Nebula, which looks like a pink rose, and the Eagle Nebula, made famous by Hubble Space Telescope as the "pillars of creation."
Each nebula is a big cloud of gas surrounding a group of stars. The hottest stars zap the gas with ultraviolet radiation. Atoms of gas absorb the energy, which knocks an electron into a higher orbit around the atom's nucleus. When the electron loses energy, it falls back into a lower orbit, emitting light, which causes the nebula to glow.
These electron energy levels were first described by Danish physicist Niels Bohr, who was born 125 years ago today. Bohr combined the emerging picture of the structure of an atom with quantum theory to deduce that electrons have set energy levels. That means the electrons must fill certain orbital slots outside the nucleus. Any jump requires the electron to either absorb or emit energy. This idea helped earn Bohr the Nobel Prize for physics in 1922.
During World War II, Bohr escaped Denmark in a British bomber. He came to America, where he helped develop the atomic bomb. After the war, he returned home and resumed his work at the University of Copenhagen, where he continued to contribute to the world of physics until his death in 1962.
Script by Damond Benningfield, Copyright 2010