A day is approximately the period of time during which the Earth completes one rotation around its axis. Inthe second was redefined in terms of the orbital motion of the Earth in the yearand was designated the SI base unit of time. The unit of measurement "day", was redefined as 86, SI seconds and symbolized d.
Night-Blooming Cereus - Protomartyr - Relatives In Descentthe second and so the day were redefined by atomic electron transition.
Day can be defined as each of the twenty-four-hour periods, reckoned from one midnight to the next, into which a week, month, or year is divided, and corresponding to a rotation of the earth on its axis. Several definitions of this universal human concept are used according to context, need and convenience. Besides the day of 24 hours 86, secondsthe word day is used Solar Year - Night & Day several different spans of time based on the rotation of the Earth around its axis.
An important one is the solar day, defined as the time it takes for the Sun to return to its culmination point its highest point in the sky. 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.
Because the Earth orbits the Sun elliptically as the Earth spins on an inclined axis, this period can be up to 7. In recent decades, the average length of a solar day on Earth has been about 86, Ancient custom has a new day start at either the rising or setting of the Sun on the local horizon Italian reckoning, for example, being 24 hours from sunset, oldstyle.
A more constant day can be defined by the Sun passing through the local meridianwhich happens at local noon upper culmination or midnight lower culmination. The exact moment is dependent on the geographical longitude, and to a lesser extent on the time of the year.
Solar Year - Night & Day is the time as indicated by modern sundials. A further improvement defines a fictitious mean Sun that moves with constant speed along the celestial equator ; the speed is the same as the average speed of the real Sun, but this removes the variation over a year as the Earth moves along its orbit around the Sun due to both its velocity and its axial tilt.
A dayunderstood 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 Lost Saviours - Chaos - Live At The Moonlight 6/2/83 to be fixed Solar Year - Night & Day , is called a stellar day.
This period of rotation is about 4 minutes less than 24 hours 23 hours 56 minutes and 4. Other planets and moons have stellar and solar days of different lengths from Earth's. A day, in the sense of daytime that is distinguished from night timeis commonly defined as the period during which sunlight directly reaches the ground, assuming that there are no local obstacles. The length of daytime averages slightly more than half of the hour day. Two effects make daytime on average longer than nights.
The Sun is not a point, but has an apparent size of about 32 minutes of arc. Additionally, the atmosphere refracts sunlight in such a way that some of it reaches the ground even when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc.
All of them from the Indo-European root dyau which explains the similarity with Latin dies though the word is known to come from the Germanic branch.
A day, symbol ddefined as 86, seconds, is not an SI unit, but is accepted for use with SI. Mainly due to tidal effectsthe Earth's rotational period is not constant, resulting in minor variations for both solar days and stellar "days". The Earth's day has increased in length over time due to tides raised by the Moon which slow Earth's rotation. Because of the way the second is defined, the mean length of a day is now about 86, The length of a day circa million years ago has been estimated from rhythmites alternating layers in Solar Year - Night & Day as having been about In order to keep the civil day aligned with the apparent movement of the Sun, a day according to Coordinated Universal Time UTC can include a negative or positive leap second.
Therefore, although typically 86, SI seconds in duration, a civil day can be either 86, or 86, SI seconds long on such a day. For civil purposes, a common clock time is typically defined for an entire region based on the local mean solar time at a central meridian. Such time zones began to be adopted about the middle of the 19th century when railroads with regularly occurring schedules The Breeze And I - Terry Snyder And The All Stars - Persuasive Percussion into use, with most major countries having adopted them by The most common convention starts the civil day at midnight : this is near the time of the lower culmination of the Sun on the central meridian What Can You Bring Me?
- Charles Wright & The Watts 103rd St Rhythm Band - Original Album Series the time zone. Such a day may be referred to as a calendar day. This was an afterglow of the short-lived movement toward I.
Praeambulum - Glenn Gould Plays Bach* - Glenn Gould Plays Bach (The Collectors Edition) decimalisation of timekeeping and the calendarwhich had been given up already due to its difficulty in transitioning from traditional, more familiar units.
The most successful alternative is the centidayequal to For most diurnal animals, the day naturally begins at dawn and ends at sunset. Humans, with their cultural norms and scientific knowledge, have employed several different conceptions of the day's boundaries.
Common convention among Infernopommes - Mesrine / Kadaverficker - Mesrine / Kadaverficker ancient Romans ancient Chinese  and in modern times is for the civil day to begin at midnight, i.
In ancient Egyptthe day was reckoned from sunrise to sunrise. The Jewish day begins at either sunset or nightfall when three second- magnitude stars appear. Medieval Europe also Solar Year - Night & Day 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 evening need to be shifted back one calendar day in modern reckoning. Prior toTurkey had two time systems: Turkish counting the hours from sunset and French counting the hours from midnight.
Validity of ticketspasses, etc. However, if a service e. For services depending on the day "closed on Sundays", "does not run on Fridays", and so on there is a risk of ambiguity. In places which experience the midnight sun polar daydaytime may extend beyond one hour period and could even extend to months.
Besides a stellar day on Earthdetermined to be 23 hours, 56 minutes and 4. From Wikipedia, the free encyclopedia. For other uses, see Day disambiguation. Further information: Leap second and Tidal acceleration. Main article: Metric time.
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