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51-469: Although yom is commonly rendered as day in English translations, the word yom can be used in different ways to refer to different time spans: Biblical Hebrew has a limited vocabulary , with fewer words compared to other languages , such as English or Spanish . This means words often have multiple meanings determined by context. Strong's Lexicon yom is Hebrew #3117 יוֹם The word Yom's root meaning

102-524: A Proto-Germanic root *dagaz . Several definitions of this universal human concept are used according to context, need, and convenience. Besides the day of 24 hours (86,400 seconds), the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the solar day , the time it takes for the Sun to return to its culmination point (its highest point in

153-538: A décade – the equivalent of a week. 3 décades make a month. Various decimal time proposals which do not redefine the day: Henri de Sarrauton's proposal kept days, and subdivided hours into 100 minutes; in Mendizábal y Tamborel's proposal, the sidereal day was the basic unit, with subdivisions made upon it; and Rey-Pailhade's proposal divided the day 100 cés. The word refers to various similarly defined ideas, such as: Mainly due to tidal deceleration –

204-511: A break in rainfall during mid-season when the Intertropical Convergence Zone or monsoon trough moves poleward of their location during the middle of the warm season; Typical vegetation in these areas ranges from moist seasonal tropical forests to savannahs . When the wet season occurs during the warm season, or summer , precipitation falls mainly during the late afternoon and early evening hours. The wet season

255-436: A day passes at a given location it experiences morning , noon , afternoon , evening , and night . This daily cycle drives circadian rhythms in many organisms, which are vital to many life processes. A collection of sequential days is organized into calendars as dates , almost always into weeks , months and years . A solar calendar organizes dates based on the Sun's annual cycle, giving consistent start dates for

306-484: 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. Days such as Christmas Eve , Halloween (“All Hallows’ Eve”), and the Eve of Saint Agnes are remnants of the older pattern when holidays began during the prior evening. The common convention among the ancient Romans , ancient Chinese and in modern times

357-500: Is a time when air quality improves, freshwater quality improves and vegetation grows significantly due to the wet season supplementing flora, leading to crop yields late in the season. Floods and rains cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients are washed away and erosion increases. The incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for

408-532: Is for the civil day to begin at midnight, i.e. 00:00, and to last a full 24 hours until 24:00, i.e. 00:00 of the next day. The International Meridian Conference of 1884 resolved That the Conference expresses the hope that as soon as may be practicable the astronomical and nautical days will be arranged everywhere to begin at midnight. In ancient Egypt the day was reckoned from sunrise to sunrise. Prior to 1926, Turkey had two time systems: Turkish , counting

459-435: Is on average around 7 minutes longer than 12 hours. Daytime is further divided into morning , afternoon , and evening . Morning occurs between sunrise and noon . Afternoon occurs between noon and sunset , or between noon and the start of evening. This period of time sees human's highest body temperature , an increase of traffic collisions , and a decrease of productivity . Evening begins around 5 or 6 pm, or when

510-585: Is that the tropics represent a ' Garden of Eden ', a heaven on Earth, a land of rich biodiversity or a tropical paradise. The alternative is that the tropics consist of wild, unconquerable nature. The latter view was often discussed in old Western literature more so than the first. Evidence suggests over time that the view of the tropics as such in popular literature has been supplanted by more well-rounded and sophisticated interpretations. Western scholars tried to theorise why tropical areas were relatively more inhospitable to human civilisations than colder regions of

561-447: Is 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). Measuring a day as such is used in astronomy . A sidereal day is about 4 minutes less than a solar day of 24 hours (23 hours 56 minutes and 4.09 seconds), or 0.99726968 of a solar day of 24 hours. There are about 366.2422 stellar days in one mean tropical year (one stellar day more than

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612-458: Is to be hot as the warm hours of a day. Thus "yom", in its context, is sometimes translated as: "time" (Gen 4:3, Is. 30:8); "year" (I Kings 1:1, 2 Chronicles 21:19, Amos 4:4); "age" (Gen 18:11, 24:1 and 47:28; Joshua 23:1 and 23:2); "always" (Deuteronomy 5:29, 6:24 and 14:23, and in 2 Chronicles 18:7); "season" (Genesis 40:4, Joshua 24:7, 2 Chronicles 15:3); epoch or 24-hour day (Genesis 1:5,8,13,19,23,31) – see "Creationism", below. Yom relates to

663-616: Is used in the name of various Jewish feast days; as, Yom Kippur , the Day of Atonement; Yom teruah (lit., day of shouting) the Feast of Trumpets (i.e. Rosh Hashannah ). Yom is also used in each of the days of the week in the Hebrew calendar . Day A day is the time period of a full rotation of the Earth with respect to the Sun . On average, this is 24 hours (86,400 seconds ). As

714-417: Is when the sun is up to 6 degrees below the horizon; nautical when it is up to 12 degrees below, and astronomical when it is up to 18 degrees below. Night is the period in which the sky is dark ; the period between dusk and dawn when no light from the sun is visible. Light pollution during night can impact human and animal life, for example by disrupting sleep. Tropics The tropics are

765-605: The Andes as far south as the northernmost parts of Chile and Perú . The climate is changing in the tropics, as it is in the rest of the world. The effects of steadily rising concentrations of greenhouse gases on the climate may be less obvious to tropical residents, however, because they are overlain by considerable natural variability. Much of this variability is driven by the El Niño-Southern Oscillation (ENSO) . The Tropics has warmed by 0.7–0.8 °C over

816-468: The Earth's natural fluctuation of a solar day , and stellar day and sidereal day (using the celestial sphere ) used for astronomy . In most countries outside of the tropics , daylight saving time is practiced, and each year there will be one 23-hour civil day and one 25-hour civil day. Due to slight variations in the rotation of the Earth, there are rare times when a leap second will get inserted at

867-544: The International Bureau of Weights and Measures (BIPM) redefined a second as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium -133 atom ". This makes the SI-based day last exactly 794,243,384,928,000 of those periods. Various decimal or metric time proposals have been made, but do not redefine

918-613: The Jewish religious calendar counts days from sunset to sunset, so the Jewish Sabbath begins at sundown on Friday . In astronomy , a day begins at noon so that observations throughout a single night are recorded as happening on the same day. In specific applications, the definition of a day is slightly modified, such as in the SI day (exactly 86,400 seconds ) used for computers and standards keeping , local mean time accounting of

969-732: The Pantropic . The system of biogeographic realms differs somewhat; the Neotropical realm includes both the Neotropics and temperate South America, and the Paleotropics correspond to the Afrotropical , Indomalayan , Oceanian , and tropical Australasian realms . Flora are plants found in a specific region at a specific time. Some well-known plants that are exclusively found in, originate from, or are often associated with

1020-567: The Solar System or other parts of the universe , a day is a full rotation of other large astronomical objects with respect to its star. 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 came into use, with most major countries having adopted them by 1929. As of 2015, throughout

1071-579: The Waterberg Biosphere of South Africa , and eastern Madagascar rainforests. Often the soils of tropical forests are low in nutrient content, making them quite vulnerable to slash-and-burn deforestation techniques, which are sometimes an element of shifting cultivation agricultural systems. In biogeography , the tropics are divided into Paleotropics (Africa, Asia and Australia) and Neotropics (Caribbean, Central America, and South America). Together, they are sometimes referred to as

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1122-619: The axial tilt of the Earth . The Tropic of Cancer is the Northernmost latitude from which the Sun can ever be seen directly overhead , and the Tropic of Capricorn is the Southernmost. This means that the tropical zone includes everywhere on Earth which is a subsolar point at least once during the solar year . Thus the maximum latitudes of the tropics have equal distances from the equator on either side. Likewise, they approximate

1173-463: The four seasons from year to year. A lunar calendar organizes dates based on the Moon 's lunar phase . In common usage, a day starts at midnight , written as 00:00 or 12:00 am in 24- or 12-hour clocks , respectively. Because the time of midnight varies between locations, time zones are set up to facilitate the use of a uniform standard time . Other conventions are sometimes used, for example

1224-451: The 24-hour day. Two effects make daytime on average longer than night. 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. Thus, daytime

1275-454: The Moon's gravitational pull slowing down the Earth's rotation – the Earth's rotational period is slowing. Because of the way the second is defined, the mean length of a solar day is now about 86,400.002 seconds, and is increasing by about 2 milliseconds per century. Since the rotation rate of the Earth is slowing, the length of a SI second fell out of sync with a second derived from

1326-406: The Sun (due to both its velocity and its axial tilt). In terms of Earth's rotation, the average day length is about 360.9856°. A day lasts for more than 360° of rotation because of the Earth's revolution around the Sun. With a full year being slightly more than 360 days, the Earth's daily orbit around the Sun is slightly less than 1°, so the day is slightly less than 361° of rotation. Elsewhere in

1377-399: The angle of the Earth's axial tilt. This angle is not perfectly fixed, mainly due to the influence of the moon, but the limits of the tropics are a geographic convention, and their variance from the true latitudes is very small. Many tropical areas have both a dry and a wet season. The wet season , rainy season or green season is the time of year, ranging from one or more months when most of

1428-459: The average annual rainfall in a region falls. Areas with wet seasons are disseminated across portions of the tropics and subtropics , some even in temperate regions. Under the Köppen climate classification , for tropical climates , a wet-season month is defined as one or more months where average precipitation is 60 mm (2.4 in) or more. Some areas with pronounced rainy seasons see

1479-437: The average length of a solar day on Earth has been about 86,400.002 seconds (24.000 000 6 hours). There are currently about 365.2421875 solar days in one mean tropical year . Ancient custom has a new day starting at either the rising or setting of the Sun on the local horizon (Italian reckoning, for example, being 24 hours from sunset, old style). The exact moment of, and the interval between, two sunrises or sunsets depends on

1530-409: The concept of time. Yom is not just for day, days, but for time in general. How yom is translated depends on the context of its use with other words in the sentence around it, using hermeneutics . The word day is used somewhat the same way in the English language, examples: "In my grandfather's day, cars did not go very fast" or "In the day of the dinosaurs there were not many mammals." The word Yom

1581-545: The day's boundaries. In the Hebrew Bible , Genesis 1:5 defines a day in terms of "evening" and "morning" before recounting the creation of the Sun to illuminate it: "And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day." The Jewish day begins at either sunset or nightfall (when three second- magnitude stars appear). Medieval Europe also followed this tradition, known as Florentine reckoning: In this system,

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1632-431: The day, and use the day or sidereal day as a base unit. Metric time uses metric prefixes to keep time. It uses the day as the base unit, and smaller units being fractions of a day: a metric hour ( deci ) is 1 ⁄ 10 of a day; a metric minute ( milli ) is 1 ⁄ 1000 of a day; etc. Similarly, in decimal time, the length of a day is static to normal time. A day is also split into 10 hours, and 10 days comprise

1683-734: The end of a UTC day, and so while almost all days have a duration of 86,400 seconds, there are these exceptional cases of a day with 86,401 seconds (in the half-century spanning 1972 through 2022, there have been a total of 27 leap seconds that have been inserted, so roughly once every other year). The term comes from the Old English term dæġ ( /dæj/ ), with its cognates such as dagur in Icelandic , Tag in German , and dag in Norwegian , Danish , Swedish and Dutch – all stemming from

1734-460: The geographic region; these usages ought not be confused. The Earth's axial tilt is currently around 23.4° , and therefore so are the latitudes of the tropical circles , marking the boundary of the tropics: specifically, ±23°26′09.8″ (or 23.43605°). The northern one is called the Tropic of Cancer , and the southern is the Tropic of Capricorn . As the Earth's axial tilt changes, so too do

1785-409: The geographical position ( longitude and latitude, as well as altitude), and the time of year (as indicated by ancient hemispherical sundials ). A more constant day can be defined by the Sun passing through the local meridian , which 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

1836-502: The hours from sunset, and French , counting the hours from midnight. Humans have divided the day in rough periods, which can have cultural implications, and other effects on humans' biological processes. The parts of the day do not have set times; they can vary by lifestyle or hours of daylight in a given place. Daytime is the part of the day during which sunlight directly reaches the ground, assuming that there are no obstacles. The length of daytime averages slightly more than half of

1887-961: The last century—only slightly less than the global average—but a strong El Niño made 1998 the warmest year in most areas, with no significant warming since. Climate models predict a further 1–2 °C warming by 2050 and 1–4 °C by 2100. Tropical plants and animals are those species native to the tropics. Tropical ecosystems may consist of tropical rainforests , seasonal tropical forests , dry (often deciduous) forests , spiny forests, deserts , savannahs, grasslands and other habitat types. There are often wide areas of biodiversity , and species endemism present, particularly in rainforests and seasonal forests. Some examples of important biodiversity and high-endemism ecosystems are El Yunque National Forest in Puerto Rico , Costa Rican and Nicaraguan rainforests, Amazon Rainforest territories of several South American countries, Madagascar dry deciduous forests ,

1938-559: The number of solar days). Besides a stellar day on Earth , other bodies in the Solar System have day times, the durations of these being: In the International System of Units (SI), a day not an official unit, but is accepted for use with SI . A day, with symbol d, is defined using SI units as 86,400 seconds; the second is the base unit of time in SI units . In 1967–68, during the 13th CGPM (Resolution 1),

1989-719: The overhead sun, the tropics receive the most solar energy over the course of the year, and consequently have the highest temperatures on the planet. Even when not directly overhead, the sun is still close to overhead throughout the year, therefore the tropics also have the lowest seasonal variation on the planet; "winter" and "summer" lose their contrast. Instead, seasons are more commonly divided by precipitation variations than by temperature variations. The tropics maintain wide diversity of local climates, such as rain forests , monsoons , savannahs , deserts , and high altitude snow-capped mountains . The word "tropical" can specifically refer to certain kinds of weather , rather than to

2040-524: The placement of leap seconds. Leap seconds are announced in advance by the International Earth Rotation and Reference Systems Service (IERS) , which measures the Earth's rotation and determines whether a leap second is necessary. Discovered by paleontologist John W. Wells , the day lengths of geological periods have been estimated by measuring sedimentation rings in coral fossils , due to some biological systems being affected by

2091-472: The regions of Earth surrounding the Equator , where the sun may shine directly overhead . This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's axial tilt ; the width of the tropics (in latitude) is twice the tilt. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone ). Due to

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2142-409: The rotational period. This arose the need for leap seconds , which insert extra seconds into Coordinated Universal Time (UTC) . Although typically 86,400 SI seconds in duration, a civil day can be either 86,401 or 86,399 SI seconds long on such a day. Other than the two-millisecond variation from tidal deceleration, other factors minutely affect the day's length , which creates an irregularity in

2193-506: The sky). Due to an orbit's eccentricity, the Sun resides in one of the orbit's foci instead of the middle. Consequently, due to Kepler's second law , the planet travels at different speeds at various positions in its orbit, and thus a solar day is not the same length of time throughout the orbital year. Because the Earth moves along an eccentric orbit around the Sun while the Earth spins on an inclined axis, this period can be up to 7.9 seconds more than (or less than) 24 hours. In recent decades,

2244-418: The sun sets, and ends when one goes to bed. Twilight is the period before sunrise and after sunset in which there is natural light but no direct sunlight. The morning twilight begins at dawn and ends at sunrise, while the evening twilight begins at sunset and ends at dusk . Both periods of twilight can be divided into civil twilight , nautical twilight , and astronomical twilight . Civil twilight

2295-431: The tide. The length of a day at the Earth's formation is estimated at 6 hours. Arbab I. Arbab plotted day lengths over time and found a curved line. Arbab attributed this to the change of water volume present affecting Earth's rotation. 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

2346-401: The time of the year. The length of such a day is nearly constant (24 hours ± 30 seconds). This 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

2397-516: The tropical and polar circles . The tropics constitute 39.8% of Earth's surface area and contain 36% of Earth's landmass . As of 2014 , the region was home also to 40% of the world's population , and this figure was then projected to reach 50% by 2050. Because of global warming , the weather conditions of the tropics are expanding with areas in the subtropics , having more extreme weather events such as heatwaves and more intense storms. These changes in weather conditions may make certain parts of

2448-469: The tropics include: Tropicality refers to the image of the tropics that people from outside the tropics have of the region, ranging from critical to verging on fetishism. Tropicality gained renewed interest in geographical discourse when French geographer Pierre Gourou published Les pays tropicaux ( The Tropical World in English), in the late 1940s. Tropicality encompassed two major images. One,

2499-568: The tropics uninhabitable. The word "tropic" comes via Latin from Ancient Greek τροπή ( tropē ), meaning "to turn" or "change direction". The tropics are defined as the region between the Tropic of Cancer in the Northern Hemisphere at 23°26′09.8″ (or 23.43605°) N and the Tropic of Capricorn in the Southern Hemisphere at 23°26′09.8″ (or 23.43605°) S; these latitudes correspond to

2550-726: The wetter regime. The previous dry season leads to food shortages into the wet season, as the crops have yet to mature. However, regions within the tropics may well not have a tropical climate. Under the Köppen climate classification, much of the area within the geographical tropics is classed not as "tropical" but as "dry" ( arid or semi-arid ), including the Sahara Desert , the Atacama Desert and Australian Outback . Also, there are alpine tundra and snow-capped peaks, including Mauna Kea , Mount Kilimanjaro , Puncak Jaya and

2601-545: The world, 40 such zones are now in use: the central zone, from which all others are defined as offsets, is known as UTC+00 , which uses Coordinated Universal Time (UTC) . 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 of the time zone. Such a day may be called a calendar day . A day is commonly divided into 24 hours, with each hour being made up of 60 minutes, and each minute composed of 60 seconds. A sidereal day or stellar day

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