Space Travel
09, Feb, 2012

Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.

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Term Definition
D Lines
A close pair of strong spectral lines in the yellow region of the spectrum of sodium. The name comes from the identifying letters given by Joseph von Fraunhofer to prominent absorption lines in the solar spectrum. The wavelengths are 589.0 and 589.6 nanometres. See also: Fraunhofer lines.