# Year/Related Articles

From Citizendium

< Year

*See also changes related to Year, or pages that link to Year or to this page or whose text contains "Year".*

## Parent topics

- Astronomy [r]: The study of objects and processes in the observable universe, e.g. stars, planets, comets or asteroids.
^{[e]} - Planet [r]: A cosmic body orbiting a star.
^{[e]} - Earth [r]:
*Please do not use this term in your topic list, because there is no single article for it. Please substitute a more precise term. See Earth (disambiguation) for a list of available, more precise, topics. Please add a new usage if needed.* - Calendar [r]: A method used for keeping time on a scale of years.
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## Subtopics

- 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]} - Equinox [r]:
*Add brief definition or description* - Aphelion [r]:
*Add brief definition or description* - Perihelion [r]:
*Add brief definition or description* - Leap year [r]:
*Add brief definition or description*

- Light day [r]: Distance that light travels in a vacuum in one day; 1 light day = 25,902,068,371,200 m = 2.5902067 * 10
^{13}m.^{[e]} - Light hour [r]: Distance that the light travels in vacuum in one hour, 1.0792528 * 10
^{12}m^{[e]} - Light minute [r]: Distance that light travels in vacuum in one minute; 17,987,547,480 m = 1.7987547 * 10
^{10}m.^{[e]} - Light second [r]: Distance that light travels in vacuum in one second; 2.99792458 * 10
^{8}m.^{[e]} - Light week [r]: Distance that light travels in a vacuum in one week; 1 light week = 1.81314469 * 10
^{11}km.^{[e]} - Light year [r]: Distance that light travels in vacuum in one year; 9,460,730,472,580.800 km = 9.4607304 * 10
^{12}km.^{[e]} - Mathematics [r]: The study of quantities, structures, their relations, and changes thereof.
^{[e]} - Perennial plant [r]: A plant that lives for more than two years.
^{[e]} - Sundial [r]: An instrument for measuring time, using the position of the sun in the sky.
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