Earth's rotation in the context of Earth Rotation Angle

Land, also known as dry land, ground, or earth, is the solid terrestrial surface of Earth not submerged by the ocean or another body of water. It makes up 29.2% of Earth's surface and includes all continents and islands. Earth's land surface is almost entirely covered by regolith, a layer of rock, soil, and minerals that forms the outer part of the crust. Land plays an important role in Earth's climate system, being involved in the carbon cycle, nitrogen cycle, and water cycle. One-third of land is covered in trees, another third is used for agriculture, and one-tenth is covered in permanent snow and glaciers. The remainder consists of desert, savannah, and prairie.

Land terrain varies greatly, consisting of mountains, deserts, plains, plateaus, glaciers, and other landforms. In physical geology, the land is divided into two major categories: Mountain ranges and relatively flat interiors called cratons. Both form over millions of years through plate tectonics. Streams – a major part of Earth's water cycle – shape the landscape, carve rocks, transport sediments, and replenish groundwater. At high elevations or latitudes, snow is compacted and recrystallized over hundreds or thousands of years to form glaciers, which can be so heavy that they warp the Earth's crust. About 30 percent of land has a dry climate, due to losing more water through evaporation than it gains from precipitation. Since warm air rises, this generates winds, though Earth's rotation and uneven sun distribution also play a part.

The Southern Hemisphere is the half (hemisphere) of Earth that is south of the equator. It contains all or part of five continents (the whole of Antarctica, the whole of Australia, about 90% of South America, about one-third of Africa, and some islands off the continental mainland of Asia) and four oceans (the whole Southern Ocean, the majority of the Indian Ocean, the South Atlantic Ocean, and the South Pacific Ocean), as well as New Zealand and most of the Pacific Islands in Oceania. Its surface is 80.9% water, compared with 60.7% water in the Northern Hemisphere, and it contains 32.7% of Earth's land. More than 850 million people live in the Southern Hemisphere, representing around 10–12% of the total global human population.

Owing to the tilt of Earth's rotation relative to the Sun and the ecliptic plane, summer is from December to February (inclusive) and winter is from June to August (inclusive). September 22 or 23 is the vernal equinox and March 20 or 21 is the autumnal equinox. The South Pole is in the centre of the southern hemispherical region.

Night, or nighttime, is the period of darkness when the Sun is below the horizon. Daylight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of sunrise and sunset. Moonlight, airglow, starlight, and light pollution dimly illuminate night. The duration of day, night, and twilight varies depending on the time of year and the latitude. Night on other celestial bodies is affected by their rotation and orbital periods. The planets Mercury and Venus have much longer nights than Earth. On Venus, night lasts about 58 Earth days. The Moon's rotation is tidally locked, rotating so that one of the sides of the Moon always faces Earth. Nightfall across portions of the near side of the Moon results in lunar phases visible from Earth.

Organisms respond to the changes brought by nightfall: darkness, increased humidity, and lower temperatures. Their responses include direct reactions and adjustments to circadian rhythms governed by an internal biological clock. These circadian rhythms, regulated by exposure to light and darkness, affect an organism's behavior and physiology. Animals more active at night are called nocturnal and have adaptations for low light, including different forms of night vision and the heightening of other senses. Diurnal animals are active during the day and sleep at night; mammals, birds, and some others dream while asleep. Fungi respond directly to nightfall and increase their biomass. With some exceptions, fungi do not rely on a biological clock. Plants store energy produced through photosynthesis as starch granules to consume at night. Algae engage in a similar process, and cyanobacteria transition from photosynthesis to nitrogen fixation after sunset. In arid environments like deserts, plants evolved to be more active at night, with many gathering carbon dioxide overnight for daytime photosynthesis. Night-blooming cacti rely on nocturnal pollinators such as bats and moths for reproduction. Light pollution disrupts the patterns in ecosystems and is especially harmful to night-flying insects.

In astronomy, diurnal motion (from Latin diurnus 'daily', from Latin diēs 'day') is the apparent motion of celestial objects (e.g. the Sun and stars) around Earth, or more precisely around the two celestial poles, over the course of one day. It is caused by Earth's rotation around its axis, so almost every star appears to follow a circular arc path, called the diurnal circle, often depicted in star trail photography.

The time for one complete rotation is 23 hours, 56 minutes, and 4.09 seconds – one sidereal day. The first experimental demonstration of this motion was conducted by Léon Foucault. Because Earth orbits the Sun once a year, the sidereal time at any given place and time will gain about four minutes against local civil time, every 24 hours, until, after a year has passed, one additional sidereal "day" has elapsed compared to the number of solar days that have gone by.

A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate (the dial) and a gnomon, which casts a shadow onto the dial. As the Sun appears to move through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The style is the time-telling edge of the gnomon, though a single point or nodus may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude.

The term sundial can refer to any device that uses the Sun's altitude or azimuth (or both) to show the time. Sundials are valued as decorative objects, metaphors, and objects of intrigue and mathematical study.

Longitude (/ˈlɒndʒɪtjuːd/, AU and UK also /ˈlɒŋɡɪ-/) is a geographic coordinate that specifies the east-west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.

Because of the Earth's rotation, there is a close connection between longitude and time measurement. Scientifically precise local time varies with longitude: a difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absolute measure of time allows longitude to be determined. Depending on the era, the absolute time might be obtained from a celestial event visible from both locations, such as a lunar eclipse, or from a time signal transmitted by telegraph or radio. The principle is straightforward, but in practice finding a reliable method of determining longitude took centuries and required the effort of some of the greatest scientific minds.

Geodesy or geodetics is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies, such as planets or circumplanetary systems.

Geodynamical phenomena, including crustal motion, tides, and polar motion, can be studied by designing global and national control networks, applying space geodesy and terrestrial geodetic techniques, and relying on datums and coordinate systems.

90°N 0°E / 90°N 0°E / 90; 0

The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the Magnetic North Pole.

The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the point in the Southern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True South Pole to distinguish from the south magnetic pole.

The South Pole is by definition the southernmost point on the Earth, lying antipodally to the North Pole. It defines geodetic latitude 90° South, as well as the direction of true south. At the South Pole all directions point North; all lines of longitude converge there, so its longitude can be defined as any degree value. No time zone has been assigned to the South Pole, so any time can be used as the local time. Along tight latitude circles, clockwise is east and counterclockwise is west. The South Pole is at the center of the Southern Hemisphere. Situated on the continent of Antarctica, it is the site of the United States Amundsen–Scott South Pole Station, which was established in 1956 and has been permanently staffed since that year.

Sunset (or sundown) is the disappearance of the Sun at the end of the Sun path, below the horizon of the Earth (or any other astronomical object in the Solar System) due to its rotation. As viewed from everywhere on Earth, it is a phenomenon that happens approximately once every 24 hours, except in areas close to the poles. The equinox Sun sets due west at the moment of both the spring and autumn equinoxes. As viewed from the Northern Hemisphere, the Sun sets to the northwest (or not at all) in the spring and summer, and to the southwest in the autumn and winter; these seasons are reversed for the Southern Hemisphere.

The sunset is defined in astronomy as the moment the upper limb of the Sun disappears below the horizon. Near the horizon, atmospheric refraction causes sunlight rays to be distorted to such an extent that geometrically the solar disk is already about one diameter below the horizon when a sunset is observed.

Long-exposure, time-exposure, or slow-shutter photography involves using a long-duration shutter speed to sharply capture the stationary elements of images while blurring, smearing, or obscuring the moving elements. Long-exposure photography captures one element that conventional photography does not: an extended period of time.

The paths of bright moving objects become clearly visible—clouds form broad bands, vehicle lights draw bright streaks, stars leave trails in the sky, and water waves appear smooth. Only bright objects leave visible trails, whereas dark objects usually disappear. Boats in long exposures disappear during the daytime, but draw bright trails from their lights at night.

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 a day passes at a given location it experiences morning, 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 the four seasons from year to year. A lunar calendar organizes dates based on the Moon's lunar phase.

The gravity of Earth, denoted by g, is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation).It is a vector quantity, whose direction coincides with a plumb bob and strength or magnitude is given by the norm ${\displaystyle g=\|{\mathit {\mathbf {g} }}\|}$.

In SI units, this acceleration is expressed in metres per second squared (in symbols, m/s or m·s) or equivalently in newtons per kilogram (N/kg or N·kg). Near Earth's surface, the acceleration due to gravity, accurate to 2 significant figures, is 9.8 m/s (32 ft/s). This means that, ignoring the effects of air resistance, the vertical component of velocity of an object falling freely will increase in the downwards direction by about 9.8 metres per second (32 ft/s) every second.

A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a tropical cyclone is called a hurricane (/ˈhʌrɪkən, -keɪn/), typhoon (/taɪˈfuːn/), tropical storm, cyclonic storm, tropical depression, or simply cyclone. A hurricane is a strong tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean. A typhoon is the same thing which occurs in the northwestern Pacific Ocean. In the Indian Ocean and South Pacific, comparable storms are referred to as "tropical cyclones". In modern times, on average around 80 to 90 named tropical cyclones form each year around the world, over half of which develop hurricane-force winds of 65 kn (120 km/h; 75 mph) or more.

Tropical cyclones typically form over large bodies of relatively warm water. They derive their energy through the evaporation of water from the ocean surface, which ultimately condenses into clouds and rain when moist air rises and cools to saturation. This energy source differs from that of mid-latitude cyclonic storms, such as nor'easters and European windstorms, which are powered primarily by horizontal temperature contrasts. Tropical cyclones are typically between 100 and 2,000 km (62 and 1,243 mi) in diameter. The strong rotating winds of a tropical cyclone are a result of the conservation of angular momentum imparted by the Earth's rotation as air flows inwards toward the axis of rotation. As a result, cyclones rarely form within 5° of the equator. South Atlantic tropical cyclones are very rare due to consistently strong wind shear and a weak Intertropical Convergence Zone. In contrast, the African easterly jet and areas of atmospheric instability give rise to cyclones in the Atlantic Ocean and Caribbean Sea.

In astronomy, a guide star is a reference star used to accurately maintain the tracking by a telescope of a celestial body, whose apparent motion through the sky is primarily due to Earth's rotation.

Accurate telescope pointing and tracking is critical for obtaining good astronomical images and astrophotographs. However, because Earth rotates, the sky appears to be in a constant state of motion relative to Earth. Although this movement appears to be relatively slow when viewed with the naked eye, with the high magnification and consequently smaller field of view provided by even a small telescope, this motion becomes apparent on timescales of the order of seconds.

Rotation, rotational or rotary motion is the movement of an object that leaves at least one point unchanged. In 2 dimensions, a plane figure can rotate in either a clockwise or counterclockwise sense around a point called the center of rotation. In 3 dimensions, a solid figure rotates around an imaginary line called an axis of rotation.

The special case of a rotation with an internal axis passing through the body's own center of mass is known as a spin (or autorotation). In that case, the surface intersection of the internal spin axis can be called a pole; for example, Earth's rotation defines the geographical poles. A rotation around an axis completely external to the moving body is called a revolution (or orbit), e.g. Earth's orbit around the Sun. The ends of the external axis of revolution can be called the orbital poles.

An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on the fact that atoms have quantised energy levels, and transitions between such levels are driven by very specific frequencies of electromagnetic radiation. This phenomenon serves as the basis for the SI definition of the second:

This definition underpins the system of TAI, which is maintained by an ensemble of atomic clocks around the world. The system of UTC — the basis of civil time — implements leap seconds to allow clock time to stay within one second of Earth's rotation.

The geoid (/ˈdʒiː.ɔɪd/ JEE-oyd) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended through the continents (such as might be approximated with very narrow hypothetical canals). According to Carl Friedrich Gauss, who first described it, it is the "mathematical figure of the Earth", a smooth but irregular surface whose shape results from the uneven distribution of mass within and on the surface of Earth. It can be known only through extensive gravitational measurements and calculations. Despite being an important concept for almost 200 years in the history of geodesy and geophysics, it has been defined to high precision only since advances in satellite geodesy in the late 20th century.

The geoid is often expressed as a geoid undulation or geoidal height above a given reference ellipsoid, which is a slightly flattened sphere whose equatorial bulge is caused by the planet's rotation. Generally the geoidal height rises where the Earth's material is locally more dense and exerts greater gravitational force than the surrounding areas. The geoid in turn serves as a reference coordinate surface for various vertical coordinates, such as orthometric heights, geopotential heights, and dynamic heights (see Geodesy).