The Fourier series is the basis for much of digital signal processing, allowing you to build a signal from the sum of many sinusoids.

All earthly and celestial things emit signals. The science of signal processing, born in the 19th Century and now greatly advanced thanks to computers, allows us to better understand them.

George Cybenko, A General Orthogonalization Technique with Applications to Time Series Analysis and Signal Processing, Mathematics of Computation, Vol. 40, No. 161 (Jan., 1983), pp. 323-336 ...