Variable Phenomena
Nyquist Sampling
Harry Nyquist
(1889 – 1976)
• Consider a sine wave.
• How often do we need to sample it in order to
figure out its frequency?
If we sample with a frequency which
corresponds to once per wavelength, we
would think the sine wave is constant
If we sample 1.5 times the real frequency, we’d think the
function is a sine with a longer wavelength (the red curve)
If we sample at twice the real frequency, we get
the right answer
Nyquist Sampling:
For lossless digitization, sample at at least twice
the frequency.
Light curves of Variable Stars
Take Fourier Transform  Period
Phase Plot
Phase, in units of cycles:

t  t0

P