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Spectroscopic Resolution

You might recall that optical telescopes need a minimum resolution to differentiate between two objects a small distance apart. Similarly, for a spectrometer to be useful, it must possess a minimum spectroscopic resolution in order to distinguish between spectral lines.

Spectroscopic resolution, also referred to as frequency resolution, is simply a measure of a spectrometer's ability to differentiate between two spectral lines with a small difference in frequency. For instance, in order for a spectrometer to resolve two spectral lines separated by 10Hz, it must possess a frequency resolution equal to or below this frequency.

Low Frequency Resolution

This graph shows the 21 centimeter spectral lines of atomic hydrogen gas from the center of the Milky Way, using a spectrometer set to a low frequency resolution. The velocities represented on the horizontal axis can be easily translated into frequencies by calculating their Doppler shifts.
JPEG Image (30K); Credits

The following is a spectral line graph of the same 21 centimeter lines. The difference is that the spectrometer was set to a much higher spectral resolution.

High Frequency Resolution

Notice that each spectral line is more clearly distinguishable from its neighboring lines, and that as a whole, the shapes of the lines are better defined than in the first graph.
JPEG Image (35K); Credits

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NCSA. Last modified by 11/12/95