Noon

For other uses, see Noon (disambiguation).

Noon is 12:00 at midday. Contrary to popular belief, it is not the moment when the sun crosses the meridian. The sun does cross the meridian at noon, apparent solar time, but we live by civil time (which is either Standard Time or Daylight Saving Time depending on the time of year and local laws) which is not the same as apparent solar time. Midday is also used as a synonym for noon, although this may also be a more general term to mean around noon, or very early afternoon.

Confusion between a.m. and p.m. when referring to noon and midnight

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

Digital clocks and computers show 12 p.m. for noon. While that phrase may be used practically, it helps to understand that any particular time is actually an instant. The "p.m." shown on clock displays refers to the 12-hour period following the instant of noon, not to the instant itself. In other words, 11:59 a.m. shows until noon; at the instant of noon it flips to 12:00. Simultaneously, the a.m. flips to p.m., though, strictly speaking, p.m. applies not to the instant of noon which separates a.m. and p.m.

Some people assume that 12 a.m. and 12 p.m. signify noon and midnight, respectively. The confusion also comes from 12 a.m. seeming to be the next hour in the 10 a.m., 11 a.m. series, but 12.01 p.m. being just after noon. In addition, p.m. is often associated with night so 12 a.m. may seem to be midnight.

Etymologically speaking, a.m. means before noon (antemeridiem) and p.m. means after noon (postmeridiem) and so neither midday nor midnight are correctly referred to using a.m. or p.m..

Solar noon

Solar noon is when the sun appears the highest in the sky (nearest zenith), compared to its positions during the rest of the day. It occurs when the Sun is transitting the celestial meridian. This is also the origin of the terms ante meridiem and post meridiem as noted above. The Sun is directly overhead at solar noon at the equator on the equinoxes; at Tropic of Cancer (latitude 23° 26′ 22″ N) on the June solstice; and at Tropic of Capricorn (23° 26′ 22″ S) on the December solstice. Due to the effects of the use of standard time, daylight saving time, and the equation of time, clock noon and solar noon hardly ever coincide.

The opposite of noon is midnight.

Etymology

The word "noon" is derived from Latin nona hora, the ninth hour of the day. As the Roman day started on 6.00 a.m., at sunrise, the first hour would have been from 6.00 till 7.00 a.m and the ninth hour from 2.00 till 3.00 p.m. These hours were important in monasteries, as different prayers were held on them.

The English word "noon" originally applied at 3.00 p.m., but by 1100 AD the meaning had shifted to "midday". (see: [1])

See also

• Dipleidoscope
• Midnight
• 12-hour clock

External links

• Generate a solar noon calendar for your location

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