From classical to rock, musicians tune their instruments to a common pitch so they can play together harmoniously. For at least 80 years, that standard pitch frequency has been A440 Hz — which defines ...

Today’s most accurate clocks mark the passage of time using transitions of electrons between two energy states in an atom. Such clock transitions are typically induced by the oscillating light wave of ...

The late Bob Gray once described Earth’s atmosphere as being like a dirty window that you can only partially see through. Light passes through, but at certain frequencies the atmosphere can smother, ...