# What is a periodogram?

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*This is from material originally developed by Peter Plavchan, NStED/IPAC.*

# What is a periodogram?

A periodogram calculates the significance of different frequencies in time-series data to identify any intrinsic periodic signals.

A periodogram is similar to the Fourier Transform, but is optimized for unevenly time-sampled data, and for different shapes in periodic signals.

A periodogram is brute-force. Many different frequencies are evaluated and candidate periodic signals.

The statistical significance of each frequency is computed based upon a series of algebraic operations that depend on the particular algorithm used and periodic signal shape assumed.