Physics Classroom Frequency and Period of a Wave
This short tutorial provides a very straightforward explanation of the difference between "frequency" and "period", terms which are often misconstrued by learners in introductory physics courses. It includes a set of 11 problems designed for self-paced study, with answers provided.
website What is Sidereal Time
If you're confused about sidereal time (as most students are) this well-written article by astronomer Christopher Crockett will set you right. Dr. Crockett also explains with clarity why astronomers use sidereal day calculations to differentiate how quickly a planet spins from how fast it's traveling around the sun.