Day - Astronomy

A day (symbol: d) is a unit of time equal to 24 hours. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second. It has several definitions. Day - Definition of a day in SI. A day is defined as 86,400 SI seconds. times from 10 kiloseconds to 100 kiloseconds, night, Calculating the day of the week, Daylight saving time, season, for a discussion of daylight and darkness near the poles and the equator and places in-between, Dagr, B ...

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• Day - Definition of a day in SI
• Day - Definition of a day in astronomy
• Day - Origin
• Day - Colloquial definition of day
• Day - Introduction
• Day - Civil day
• Day - Leap seconds
• Day - Astronomy
• Day - Boundaries of the day
• Day - List of famous days
• Day - People named Day

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Different definitions of the day are based on the apparent motion of the Sun across the sky (solar day; see solar time). The reason for this apparent motion is the rotation of the Earth around its axis, as well as the revolution of the Earth in its orbit around the Sun. A day, as opposed to night, is commonly defined as the period during which sunlight directly reaches the ground, assuming that there are no local obstacles. Two effects make days on average longer than nights. The Sun is not a point, but has an apparent size of about 3 ...

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Day, Day - Definition of a day in SI, Day - Definition of a day in astronomy, Day - Origin, Day - Colloquial definition of day, Day - Introduction, Day - Civil day, Day - Leap seconds, Day - Astronomy, Day - Boundaries of the day, Day - List of famous days, Day - People named Day

Read more here: » Day: Encyclopedia II - Day - Introduction

For most diurnal animals, including Homo sapiens, the day naturally begins at dawn and ends at sunset. Humans, with our cultural norms and scientific knowledge, have supplanted Nature with several different conceptions of the day's boundaries. The Jewish day begins at either sunset or at nightfall (when three second-magnitude stars appear). Medieval Europe followed this tradition, known as Florentine reckoning: in this system, a reference like "two hours into the day" meant two hours after sunset and thus times during the eveni ...

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Day, Day - Definition of a day in SI, Day - Definition of a day in astronomy, Day - Origin, Day - Colloquial definition of day, Day - Introduction, Day - Civil day, Day - Leap seconds, Day - Astronomy, Day - Boundaries of the day, Day - List of famous days, Day - People named Day

Read more here: » Day: Encyclopedia II - Day - Boundaries of the day

For civil purposes a common clock time has been defined for an entire region based on the mean local solar time at some central meridian. Such time zones began to be adopted about the middle of the 19th century when railroads with regular schedules came into use, with most major countries having adopted them by 1929. For the whole world, 39 such time zones are now in use. The main one is "world time" or ...

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Day, Day - Definition of a day in SI, Day - Definition of a day in astronomy, Day - Origin, Day - Colloquial definition of day, Day - Introduction, Day - Civil day, Day - Leap seconds, Day - Astronomy, Day - Boundaries of the day, Day - List of famous days, Day - People named Day

Read more here: » Day: Encyclopedia II - Day - Civil day

For a given planet, there are two types of day defined in astronomy: 1 apparent sidereal day = a single rotation of a planet with respect to the distant stars (for Earth it is 23.934 solar hours or 24 sidereal hours) 1 solar day = a single rotation of a planet with respect to Sun. ...

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Day, Day - Definition of a day in SI, Day - Definition of a day in astronomy, Day - Origin, Day - Colloquial definition of day, Day - Introduction, Day - Civil day, Day - Leap seconds, Day - Astronomy, Day - Boundaries of the day, Day - List of famous days, Day - People named Day

Read more here: » Day: Encyclopedia II - Day - Definition of a day in astronomy

In order to keep the civil day aligned with the apparent movement of the Sun, positive or negative leap seconds may be inserted. A civil clock day is typically 86400 SI seconds long, but will be 86401 s or 86399 s long in the event of a leap second. Leap seconds are announced in advance by the International Earth Rotation and Reference Systems Service which measures the Earth's rotation and determines whether a leap second is necessary. Leap seconds occur only at the end of a UTC month, and have only ever been inserted a ...

See also:

Day, Day - Definition of a day in SI, Day - Definition of a day in astronomy, Day - Origin, Day - Colloquial definition of day, Day - Introduction, Day - Civil day, Day - Leap seconds, Day - Astronomy, Day - Boundaries of the day, Day - List of famous days, Day - People named Day

Read more here: » Day: Encyclopedia II - Day - Leap seconds