Spectral resolution

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The spectral resolution or resolving power of a spectrograph is a measure of its power to resolve features in the electromagnetic spectrum. It is usually defined by

R = \frac{\lambda}{\Delta\lambda},

where Δλ is the smallest difference in wavelengths that can be distinguished, at a wavelength of λ. So, for example, the Space Telescope Imaging Spectrograph (STIS) can distinguish features 0.17 nm apart at a wavelength of 1000 nm, giving it a resolving power of about 5,900.

The spectral resolution can also be expressed in terms of a velocity, and then describes the difference between velocities that can be distinguished through the Doppler effect. Then, the definition is

R = c\left (\frac {\Delta\lambda}{\lambda}\right ),

where c is the speed of light. The STIS example above then has a spectral resolution of 51 kilometres per second.

[edit] References

  1. Kim Quijano, J., et al. (2003), STIS Instrument Handbook, Version 7.0, (Baltimore: STScI)
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