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The Ultraviolet Spectrum of the Bright Galactic Star Zeta Ophiuchi


The spectrum was recorded with the Copernicus satellite (1972) by Don Morton. The abscissa (x-axis) is in units of Ångstroms and the ordinate (y-axis) is in units of counts per 14 seconds. The spectrum was recorded point by point using a photo cell. The spectrum from 1197 Å to 1254 Å, which took 20 hours to record, contains four types of features: a) the strong absorption from the interstellar hydrogen line known as Lyman alpha near 1216 Å; b) a set of very narrow, deep lines due to neutral nitrogen at 1200 Å, twice ionized silicon at 1206 Å, and once ionized sulfur just past 1250 Å, all from interstellar gas; c) a wind containing four times ionized nitrogen blowing off the surface of the star at 1000 km/second (1233 Å and 1238 Å); d) general undulations across the top which are due to absorption lines in the atmosphere of the star itself. The sharp, narrow interstellar lines, item b, actually contain two components which cannot be distinguished in this spectrum because of insufficient resolution. This is the spectrum of a star, but the dominant features are from the interstellar medium and the wind from the star. For more information about this spectrum, see Morton, D.C. 1975, ApJ, 197, 85.


Copernicus (OAO-3)


  • Zeta Ophiuchi
  • star

Spectral Type


Date Created



Image courtesy Don Morton. Reproduced by permission of the AAS.



Associated Lesson

Ultraviolet Science

This material is based upon work supported by NASA under Grant Nos. NNX09AD33G and NNX10AE80G issued through the SMD ROSES 2009 Program.

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