Noon

For other uses, seeNoon (disambiguation)."True Noon", "Noon time", and "Midday" redirect here. For the film, seeTrue Noon(film).For the song, seeNoon Time (song).For other uses, seeMidday (disambiguation).

Baku Street at Noon(1861) byAlexey Bogolyubov,showing shadows falling vertically in the city ofBaku

Noon(ormidday) is 12o'clockin thedaytime.It is written as12 noon,12:00 m.(formeridiem,literally 12:00 midday),12 p.m.(forpost meridiem,literally "after midday" ),12 pm,or12:00(using a 24-hour clock) or1200(military time). Solar noonis thetimewhen theSunappears tocontactthe local celestialmeridian.This is when the Sun reaches its apparenthighest pointin the sky, at 12 noonapparent solar timeand can be observed using asundial.Thelocal or clock timeof solar noon depends on the date,longitude,andtime zone,with Daylight Saving Time tending to place solar noon closer to 1:00pm.

Etymology

The wordnoonis derived from Latinnona hora,the ninthcanonical hourof the day, in reference to theWestern Christianliturgical termNones (liturgy),(number nine), one of theseven fixed prayer timesin traditionalChristian denominations.TheRoman and Western European medieval monastic daybegan at 6:00 a.m. (06:00) at theequinoxby modern timekeeping, so the ninth hour started at what is now 3:00 p.m. (15:00) at the equinox.In English, the meaning of the word shifted tomiddayand the time gradually moved back to 12:00 local time – that is, not taking into account the modern invention of time zones. The change began in the 12th century and was fixed by the 14th century.

Solar noon

"High noon" redirects here. For the film, seeHigh Noon.For other uses, seeHigh noon (disambiguation).

See also:Lahaina Noon

Solar noon,also known as thelocal apparent solar noonandSun transit time(informallyhigh noon),is the moment when the Sun contacts the observer's meridian (culminationormeridian transit), reaching its highest position above the horizon on that day and casting the shortest shadow. This is also the origin of the termsante meridiem(a.m.) andpost meridiem(p.m.), as noted below. The Sun is directly overhead at solar noon at theEquatoron theequinoxes,at theTropic of Cancer(latitude23°26′09.9″ N) on theJune solsticeand at theTropic of Capricorn(23°26′09.9″ S) on theDecember solstice.In theNorthern Hemisphere,north of the Tropic of Cancer, the Sun is due south of the observer at solar noon; in theSouthern Hemisphere,south of the Tropic of Capricorn, it is due north.

The elapsed time from the local solar noon of one day to the next is exactly 24 hours on only four instances in any given year. This occurs when the effects of Earth'sobliquity of eclipticand itsorbital speedaround the Sun offset each other. These four days for thecurrent epochare centered on 11 February, 13 May, 26 July, and 3 November. It occurs at only one particular line of longitude in each instance. This line varies year to year, since Earth's trueyearis not an integer number of days. This event time and location also varies due toEarth's orbitbeing gravitationally perturbed by the planets. These four 24-hourdaysoccur in both hemispheres simultaneously. The precise UTC times for these four days also mark when the opposite line of longitude, 180° away, experiences precisely 24 hours from localmidnightto local midnight the next day. Thus, four varyinggreat circlesof longitude define from year to year when a 24-hour day (noon to noon or midnight to midnight) occurs.

The two longest time spans from noon to noon occur twice each year, around 20 June (24 hours plus 13 seconds) and 21 December (24 hours plus 30 seconds).

The shortest time spans occur twice each year, around 25 March (24 hours minus 18 seconds) and 13 September (24 hours minus 22 seconds).

For the same reasons, solar noon and "clock noon" are usually not the same. Theequation of timeshows that the reading of a clock at solar noon will be higher or lower than 12:00 by as much as 16 minutes. Additionally, due to the political nature of time zones, as well as the application ofdaylight saving time,it can be off by more than an hour.

Nomenclature

Main article:12-hour clock § Confusion at noon and midnight

In the US, noon is commonly indicated by 12 p.m., and midnight by 12 a.m. While some argue that such usage is "improper"based on the Latin meaning (a.m. stands forante meridiemand p.m. forpost meridiem,meaning "before midday" and "after midday" respectively), digital clocks are unable to display anything else, and an arbitrary decision must be made. An earlier standard of indicating noon as "12M" or "12m" (for "meridies" ), which was specified in theU.S. GPOGovernment Style Manual,has fallen into relative obscurity; the current edition of the GPO makes no mention of it.However, due to the lack of an international standard, the use of "12 a.m." and "12 p.m." can be confusing. Common alternative methods of representing these times are:

• to use a 24-hour clock (00:00 and 12:00, 24:00; but never 24:01)
• to use "12 noon" or "12 midnight" (though "12 midnight" may still present ambiguity regarding the specific date)
• to specify midnight as between two successive days or dates (as in "midnight Saturday/Sunday" or "midnight December 14/15" )
• to avoid those specific times and to use "11:59 p.m." or "12:01 a.m." instead. (This is common in the travel industry to avoid confusion to passengers' schedules, especially train and plane schedules.)

See also

• Afternoon
• Analemma
• Dipleidoscope
• Hour angle
• Solar azimuth angle

External links

• Media related toNoonat Wikimedia Commons
• Generate a solar noon calendar for your location
• U.S. Government Printing Office Style Manual (2008), 30th edition
• Shows the hour and angle of sunrise, noon, and sunset drawn over a map.
• Real Sun Time- gives you an exact unique time to the sun, with yours GPS coordinates position.