You all know what a circadian rhythm is! Biological functions like sleep and wake that are synchronised to the rotation of the earth over a period of approximately 24 hours. And you would also know that there are activities that cycle at a period longer than 24 hours — like menstruation in humans, migration and hibernation in animals. And of course, activities with shorter periods like hunger.

But do you know what these cycles are called? Just learned about the exact terms and they are super cool to say out loud!

Cycles that have a shorter period than the circadian rhythms are called ultradian rhythms. The ones that have a longer period, say like annually, are called infradian rhythms.