Keywords: class-spectral-axis-v12

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## Spectrometers in radio-astronomy

Typical radio-astronomy spectrometers (e.g., correlators or Fourier transform spectrometers) deliver the brightness along a given line of sight at regularly spaced frequencies in the observatory frame. The spectrum can be represented as a set of brightness temperatures , where the frequency axis in the observatory frame is defined as

| (1)

where ( ) is the frequency at the channel , the frequency at the reference channel , and the channel spacing.