Given the question: Information: - A day is a unit of time. In common usage, it is either an interval equal to 24 hours or daytime, the consecutive period of time during which the Sun is above the horizon. The period of time during which the Earth completes one rotation with respect to the Sun is called a "solar day". Several definitions of this universal human concept are used according to context, need and convenience. In 1960, the second was redefined in terms of the orbital motion of the Earth, and was designated the SI base unit of time. The unit of measurement "day", redefined in 1960 as 86 400 SI seconds and symbolized "d", is not an SI unit, but is accepted for use with SI. A civil day is usually 86 400 seconds, plus or minus a possible leap second in Coordinated Universal Time (UTC), and occasionally plus or minus an hour in those locations that change 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?" The life patterns of humans and many other species are related to Earth's solar day and the day-night cycle (see circadian rhythms). - The hour (common symbol: h or hr, h being the international form of the symbol) is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds. It is approximately of a mean solar day. - A calendar date is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, "24 2017" is ten days after "14 2017" in the Gregorian calendar. The date of a particular event depends on the observed time zone. For example, the air attack on Pearl Harbor that began at 7:48a.m. Hawaiian time on December 7, 1941, took place at 3:18a.m. December 8 in Japan (Japan Standard Time). - Earth, otherwise known as the world, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets. - The horizon or skyline is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting intersection of earth and sky is called the "visible horizon". When looking at a sea from a shore, the part of the sea closest to the horizon is called the "offing". The word "horizon" derives from the Greek " " "horizn kyklos", "separating circle", from the verb "horiz", "to divide", "to separate", and that from "" ("oros"), "boundary, landmark". - A week is a time unit equal to seven days. It is the standard time period used for cycles of work days and rest days in most parts of the world, mostly alongside (but not strictly part of) the Gregorian calendar. - The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units and their physical quantities are the metre for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the candela for luminous intensity, and the mole for amount of substance. - A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in plants, animals, fungi, and cyanobacteria. - The second (symbol: s) (abbreviated s or sec) is the base unit of time in the International System of Units (SI). It is qualitatively defined as the "second" division of the hour by sixty, the first division by sixty being the minute. SI definition of second is "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom". Seconds may be measured using a mechanical, electrical or an atomic clock. - Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through Earth's atmosphere, and is obvious as daylight when the Sun is above the horizon. When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, it is experienced as diffused light. The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an "Average over the entire earth" of "164 Watts per square meter over a 24 hour day". - On Earth, daytime is roughly the period on any given point of the planet's surface during which it experiences natural illumination from indirect or (especially) direct sunlight. - Night or nighttime ("sp." night-time or night time) is the period of time between the sunset and the sunrise when the Sun is below the horizon. - A rotation is a circular movement of an object around a center (or point) of rotation . A three-dimensional object always rotates around an imaginary line called a rotation axis. If the axis passes through the body's center of mass, the body is said to rotate upon itself, or spin. A rotation about an external point, e.g. the Earth about the Sun, is called a revolution or orbital revolution, typically when it is produced by gravity. The axis is called a pole. - Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future. Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as the fourth dimension, along with the three spatial dimensions. - Daylight saving time (DST) or summer time is the practice of advancing clocks during summer months by one hour so that evening daylight lasts an hour longer, while sacrificing normal sunrise times. Typically, regions with summer time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time. - A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earth's rotation drifts away from atomic time because of irregularities in the Earth's rate of rotation. Since this system of correction was implemented in 1972, 27 leap seconds have been inserted, the most recent on December 31, 2016 at 23:59:60 UTC. - Nychthemeron / nkmrn / , occasionally nycthemeron or nuchthemeron ( Greek from the words nykt - '' night '' , and hemera '' day , daytime '' ) , is a period of 24 consecutive hours . It is sometimes used , especially in technical literature , to avoid the ambiguity inherent in the term day . It is the period of time that a calendar normally labels with a date , although a nychthemeron simply designates a time - span that can start at any time , not just midnight . After reading the paragraphs above, we are interested in knowing the entity with which 'nychthemeron' exhibits the relationship of 'instance of'. Find the answer from the choices below. Choices: - atmosphere - atomic clock - calendar - calendar date - clock - component - concept - cycle - day - electric current - electromagnetic radiation - gregorian calendar - harbor - intersection - interval - keep - line - material - may - measurement - meter - motion - object - order - period - planet - point - pole - practice - process - quantity - reference - revolution - set - seven - species - spring - symbol - system - term - three - time - time zone - two - unit of time - verb - word - work
The answer is:
unit of time