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/day/, n.1. the interval of light between two successive nights; the time between sunrise and sunset: Since there was no artificial illumination, all activities had to be carried on during the day.2. the light of day; daylight: The owl sleeps by day and feeds by night.3. Astron.a. Also called mean solar day. a division of time equal to 24 hours and representing the average length of the period during which the earth makes one rotation on its axis.b. Also called solar day. a division of time equal to the time elapsed between two consecutive returns of the same terrestrial meridian to the sun.c. Also called civil day. a division of time equal to 24 hours but reckoned from one midnight to the next. Cf. lunar day, sidereal day.4. an analogous division of time for a planet other than the earth: the Martian day.5. the portion of a day allotted to work: an eight-hour day.6. a day on which something occurs: the day we met.7. (often cap.) a day assigned to a particular purpose or observance: New Year's Day.8. a time considered as propitious or opportune: His day will come.9. a day of contest or the contest itself: to win the day.10. Often, days. a particular time or period: the present day; in days of old.11. Usually, days. period of life or activity: His days are numbered.12. period of existence, power, or influence: in the day of the dinosaurs.13. light1 (def. 19a).14. call it a day, to stop one's activity for the day or for the present; quit temporarily: After rewriting the paper, she decided to call it a day.15. day in, day out, every day without fail; regularly: They endured the noise and dirt of the city day in, day out. Also, day in and day out.[bef. 950; ME; OE daeg; c. G Tag]
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ITime required for a celestial body to turn once on its axis; especially, the period of the Earth's rotation.The sidereal day (see sidereal period) is the time required for the Earth to rotate once relative to the background of the stars (i.e., the time between two observed passages of a star over the same meridian of longitude). The apparent solar day is the time between two successive transits of the Sun over the same meridian. Because the orbital motion of the Earth makes the Sun seem to move slightly eastward each day relative to the stars, the solar day is about four minutes longer than the sidereal day. The mean solar day is the average value of the solar day, which changes slightly in length during the year as the Earth's speed in its orbit varies.II(as used in expressions)All Saints' DayAll Souls' DayApril Fools' DayAll Fools' DayD DayDay DorisDay DorothyDay Lewis CecilHershey Alfred DayJudgment Day ofMother's Day and Father's DayNew Year's DayO'Connor Sandra DaySandra DaySaint Bartholomew's Day Massacre ofSix Day WarValentine's DayReorganized Church of Jesus Christ of Latter Day SaintsSeven Days' Battles* * *
time required for a celestial body to turn once on its axis; especially the period of the Earth's rotation. The sidereal day is the time required for the Earth to rotate once relative to the background of the stars—i.e., the time between two observed passages of a star over the same meridian of longitude. The apparent solar day is the time between two successive transits of the Sun over the same meridian. Because the orbital motion of the Earth makes the Sun seem to move slightly eastward each day relative to the stars, the solar day is about four minutes longer than the sidereal day; i.e., the mean solar day is 24 hours 3 minutes 56.555 seconds of mean sidereal time; more usually the sidereal day is expressed in terms of solar time, being 23 hours 56 minutes 4 seconds of mean solar time long. The mean solar day is the average value of the solar day, which changes slightly in length during the year as Earth's speed in its orbit varies.The solar day is the fundamental unit of time in both astronomical practice and civil life. It begins at midnight and runs through 24 hours, until the next midnight. A day is commonly divided into two sets of 12 hours for ordinary timekeeping purposes; those hours from midnight to noon are designated AM (ante meridiem, “before noon”), and those from noon to midnight are designated PM (post meridiem, “after noon”). In law the word day, unless qualified, means the 24 hours between midnight and midnight, rather than the daylight hours between sunrise and sunset.* * *
Universalium. 2010.
