Search results
Results from the WOW.Com Content Network
The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: a.m. (from Latin ante meridiem, translating to "before midday") and p.m. (from Latin post meridiem, translating to "after midday"). [1] [2] Each period consists of 12 hours numbered: 12 (acting as 0), [3] 1, 2, 3, 4
The prime meridian of the Moon lies directly in the middle of the face of the Moon visible from Earth and passes near the crater Bruce. The prime meridian of Mars was established in 1971 [35] and passes through the center of the crater Airy-0, although it is fixed by the longitude of the Viking 1 lander, which is defined to be 47.95137°W. [36]
This abbreviation comes as a result of the International Telecommunication Union and the International Astronomical Union wanting to use the same abbreviation in all languages. [4] The compromise that emerged was UTC , [ 5 ] which conforms to the pattern for the abbreviations of the variants of Universal Time (UT0, UT1, UT2, UT1R, etc.).
Longitude, being up to 180° east or west of a prime meridian, is mathematically related to time differences up to 12 hours by a factor of 15. Thus, a time differential (in hours) between two points is multiplied by 15 to obtain a longitudinal difference (in degrees).
Nautical GMT began 24 hours before astronomical GMT, at least until 1805 in the Royal Navy, but persisted much later elsewhere because it was mentioned at the 1884 conference. Greenwich was chosen because by 1884 two-thirds of all nautical charts and maps already used it as their prime meridian. [6]
The conference therefore established the Greenwich Meridian as the prime meridian and Greenwich Mean Time (GMT) as the world's time standard. The U.S. time-zone system grew from this, in which all zones referred back to GMT on the prime meridian. [2]
2.4 hours, or 144 minutes. One-tenth of a day is 1 dd (deciday), also called "gēng" in tradidional Chinese timekeeping. day: 24 h: Longest unit used on stopwatches and countdowns. The SI day is exactly 86 400 seconds. week: 7 d: Historically sometimes also called "sennight". decaday 10 d (1 Dd) 10 days.
Hours under 10 should have a leading zero (08:15). The time 00:00 refers to midnight at the start of a date, 12:00 to noon, and 24:00 to midnight at the end of a date, but 24 should not be used for the first hour of the next day (e.g. use 00:10 for ten minutes after midnight, not 24:10).