| − | In [[geology]], an epoch is a subdivision of a geological period (as the Cambrian, Ordovician, and so on). In [[astronomy]], an epoch is an arbitrary time for reckoning orbital elements, positions, and so on. In [[physics]], the epoch is the displacement from zero (that is to say, the position) at zero time (that is, the start) of a body placed into simple harmonic motion. | + | In [[geology]], an epoch is a subdivision of a geological period (as the [[Cambrian]], [[Ordovician]], and so on). In [[astronomy]], an epoch is an arbitrary time for reckoning orbital elements, positions, and so on. In [[physics]], the epoch is the displacement from zero (that is to say, the position) at zero time (that is, the start) of a body placed into simple harmonic motion. |