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# Second (physics)/Related Articles  Main Article Discussion Related Articles  [?] Bibliography  [?] External Links  [?] Citable Version  [?] A list of Citizendium articles, and planned articles, about Second (physics).

## Parent topics

• Time [r]: A fundamental quantity in physics - that what differs always between two inspections of the same system by the same observer. [e]

## Other related topics

• Year [r]: A unit of time measurement that corresponds to one revolution of the earth around the sun, approximately 365¼ days. [e]
• Month [r]: Unit of time originally corresponding approximately to one cycle of the moon's phases, or about 30 days or 4 weeks. [e]
• Week [r]: Time unit equal to a number of days, now usually seven calendar days, previously weeks of between 4 and 20 days have been used historically in various places. [e]
• Day [r]: Defined as 86,400 seconds, using the SI definition of second. [e]
• Hour [r]: Add brief definition or description
• Minute [r]: Add brief definition or description
• Metric units [r]: Obsolete term for a system of units in which the unit of length is the meter, the unit of mass the kilogram, and the unit of time the second. [e]
• Hertz [r]: The international (SI) unit of frequency, with units of inverse seconds, commonly called cycles per seocond. [e]
• Frequency [r]: For a periodic (i.e., repeating) phenomena, the number of repetitions per unit of time, usually one second; measured in Hertz [e]
• Electromagnetic wave [r]: A change, periodic in space and time, of an electric field E(r,t) and a magnetic field B(r,t); a stream of electromagnetic waves, referred to as electromagnetic radiation, can be seen as a stream of massless elementary particles, named photons. [e]
• Light second [r]: Distance that light travels in vacuum in one second; 2.99792458 * 108m. [e]