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  "body": "\n## Summary\n\nThe periodogram of a finite [[time series|EA3MF4VTEH]] measures how much of the variation of the series is due to oscillations at each frequency.\nIt is the squared modulus of the discrete Fourier transform of the data, suitably scaled.\nIt is the basic estimate of the spectral density of a stationary process and the starting point of spectral analysis.\nBy itself, however, it is a noisy estimate.\n\n## Explanations\n\n### L1 human\n\nA series that rises and falls every $12$ months has a strong rhythm at the frequency of one cycle per year.\nThe periodogram scans through all frequencies and asks how well a sine wave of that frequency fits the data.\nFrequencies with a good fit show up as peaks.\nFor example, for monthly sales with a December peak, the periodogram has a peak at the frequency $2\\pi/12$ radians per month.\n",
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