Spark
Loading...

Object Cards for the 13 Officially Listed Targets

In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature.

Figures (7)

Opacity of the Earth's atmosphere for different wavelengths of electromagnetic radiation. The atmosphere blocks some wavelengths but it is mostly transparent for visible light and a wide range of radio waves.
Black body curves for various temperatures.
Redshift and blueshift
The Star-Spectroscope of the Lick Observatory in 1898. Designed by James Keeler and constructed by John Brashear.
With a blazed grating, incident light is separated into several diffraction orders which separate different wavelengths apart (red and blue lines), excepting the 0-th order (black).
Two stars of different size orbiting the center of mass. The spectrum can be seen to split depending on the position and velocity of the stars.
Optical spectrum of Comet Hyakutake.

Key Points

  • Other modern stellar classification systems, such as the UBV system, are based on color indices—the measured differences in three or more color magnitudes.
  • In the MK system, a luminosity class is added to the spectral class using Roman numerals.
  • Spectroscopy is also used to study the physical properties of many other types of celestial objects such as planets, nebulae, galaxies, and active galactic nuclei.
  • The Hertzsprung–Russell diagram, which the MK system is based on, is observational in nature so these remnants cannot easily be plotted on the diagram, or cannot be placed at all.

Terms

Tap a term for a plain-language explanation.

Sources & licensing(4)