An Etymological Dictionary of Astronomy and Astrophysics
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The rate at which the rotation period of a → pulsar changes over time. This quantity, dP/dT, can range from as small as 0.05 picoseconds per year (1.5 x 10^-21 seconds per second) to as large as about 10 milliseconds per year (4.2 x 10^-10 seconds per second). For the → Crab pulsar, the period derivative is 4.2 x 10^-13 s s^-1, implying a decrease in the star's → rotation energy of about 4.5 x 10³⁸ erg s^-1. Period derivative is a very important parameter for the determination of the pulsar age.

→ period; → derivative.