A day is a unit of time. In common usage, it is an interval equal to 24 hours. It also can mean the consecutive period of time during which the Sun is above the horizon of a location, also known as daytime. The period of time measured from local noon to the following local noon is called a solar day.
Several definitions of this universal human concept are used according to context, need and convenience. In 1967, the second was redefined in terms of the wavelength of light, and it became the SI base unit of time. The unit of measurement for time called "day", redefined in 1967 as 86,400 SI seconds and symbolized d, is not an SI unit, but it is accepted for use with SI. A civil day is usually also 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time UTC, and, in some locations, occasionally plus or minus an hour when changing from or to daylight saving time. The word day may also refer to a day of the week or to a calendar date, as in answer to the question "On which day?" Day also refers to the part of the day that is not night — also known as 'daytime'. The life patterns of humans and many other species are related to Earth's solar day and the cycle of day and night (see circadian rhythms).
The average length of a solar day on Earth is about 86,400 seconds (24 hours) and there are about 365.2422 solar days in one mean tropical year. Because celestial orbits are not perfectly circular, and thus objects travel at different speeds at various positions in their orbit, a solar day is not the same length of time throughout the orbital year. A day, understood as the span of time it takes for the Earth to make one entire rotation with respect to the celestial background or a distant star (assumed to be fixed), is called stellar day. This period of rotation is about 4 minutes less than 24 hours and there are about 366.2422 in one mean tropical year (one more stellar day than the number of solar days). Mainly due to tidal effects, the Earth's rotational period is not constant, resulting in further minor variations for both solar days and stellar 'days'. Other planets and moons also have stellar and solar days.
Read more about Day: Introduction, Etymology, International System of Units (SI), Astronomy, Colloquial, Civil Day, Leap Seconds, Boundaries of The Day, 24 Hours Vs Daytime
Other articles related to "day, days":
... To distinguish between a full day and daytime, the word nychthemeron (from Greek for a night and a day) may be used in English for the former, or more ... Other languages also have a separate word for a full day, such as vuorokausi in Finnish, ööpäev in Estonian, dygn in Swedish, døgn in Danish, døgn in Norwegian, sólarhringur in ... In Italian, giorno is used to indicate a full day, while dì means daytime ...
... Yom Yerushalayim (יום ירושלים) — 28 Iyar Jerusalem Day marks the 1967 reunification of Jerusalem and The Temple Mount under Jewish rule during the Six-Day War almost 1900 years after the ...
... In Western Christianity, All Souls' Day, also known as the Commemoration of All Faithful Departed, is observed principally in the Catholic Church ... The Eastern Orthodox Church observes several All Souls' Days during the year ... languages the celebration, not necessarily on the same date, is known as Day of the Dead ...
... Christian Feast Day Engelbert II of Berg Herculanus of Perugia Prosdocimus Vicente Liem de la Paz Willibrord November 7 (Eastern Orthodox liturgics) Commemoration Day, the anniversary of Ben Ali's succession ... (Tunisia) National Day, after Treaty of Pyrenees ... (Northern Catalonia) National Revolution and Solidarity Day (Bangladesh) October Revolution Day (the Soviet Union (former, official), modern Russia (unofficial), Belarus, Kyrgyzstan) ...
... February 24 is the 55th day of the year in the Gregorian calendar ... There are 310 days remaining until the end of the year (311 in leap years) ... By Roman custom, February 24 is the day added to a leap year in the Julian calendar ...
Famous quotes containing the word day:
“The first man to discover Chinook salmon in the Columbia, caught 264 in a day and carried them across the river by walking on the backs of other fish. His greatest feat, however, was learning the Chinook jargon in 15 minutes from listening to salmon talk.”
—State of Oregon, U.S. public relief program (1935-1943)
“I often used to think myself in the case of the fox-hunter, who, when he had toiled and sweated all day in the chase as if some unheard-of blessing was to crown his success, finds at last all he has got by his labor is a stinking nauseous animal. But my condition was yet worse than his; for he leaves the loathsome wretch to be torn by his hounds, whilst I was obliged to fondle mine, and meanly pretend him to be the object of my love.”
—Sarah Fielding (1710–1768)
“The light which puts out our eyes is darkness to us. Only that day dawns to which we are awake. There is more day to dawn. The sun is but a morning star.”
—Henry David Thoreau (1817–1862)