A glacier is a persistent body of dense ice that is constantly moving under its own weight, it forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses and they abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice, between 35°N and 35°S, glaciers occur only in the Himalayas, Rocky Mountains, a few high mountains in East Africa, New Guinea and on Zard Kuh in Iran. Glaciers cover about 10 percent of Earths land surface, continental glaciers cover nearly 13,000,000 km2 or about 98 percent of Antarcticas 13,200,000 km2, with an average thickness of 2,100 m. Greenland and Patagonia have huge expanses of continental glaciers, Glacial ice is the largest reservoir of fresh water on Earth. Within high altitude and Antarctic environments, the temperature difference is often not sufficient to release meltwater. A large piece of compressed ice, or a glacier, appears blue as large quantities of water appear blue and this is because water molecules absorb other colors more efficiently than blue.
The other reason for the color of glaciers is the lack of air bubbles. Air bubbles, which give a color to ice, are squeezed out by pressure increasing the density of the created ice. The word Glaceon is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, the processes and features caused by or related to glaciers are referred to as glacial. The process of establishment and flow is called glaciation. The corresponding area of study is called glaciology, Glaciers are important components of the global cryosphere. Glaciers are categorized by their morphology, thermal characteristics, and behavior, cirque glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier, a large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field. Ice caps have a less than 50,000 km2 by definition. Glacial bodies larger than 50,000 km2 are called ice sheets or continental glaciers, several kilometers deep, they obscure the underlying topography.
Only nunataks protrude from their surfaces, the only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of water, enough that if both melted, global sea levels would rise by over 70 m
Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, snowflakes take on a variety of shapes, basic among these are platelets, needles and rime. As snow accumulates into a snowpack, it may blow into drifts, over time, accumulated snow metamorphoses, by sintering and freeze-thaw. Where the climate is cold enough for year-to-year accumulation, a glacier may form, snow typically melts seasonally, causing runoff into streams and rivers and recharging groundwater. Major snow-prone areas include the regions, the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture. In the Southern Hemisphere, snow is confined primarily to mountainous areas, Snow affects ecosystems, as well, by providing an insulating layer during winter under which plants and animals are able to survive the cold. Snow develops in clouds that themselves are part of a weather system.
The physics of snow crystal development in clouds results from a set of variables that include moisture content. The resulting shapes of the falling and fallen crystals can be classified into a number of shapes and combinations. Occasionally, some plate-like and stellar-shaped snowflakes can form under clear sky with a cold temperature inversion present. Two additional and locally productive sources of snow are lake-effect storms and elevation effects, miid-latitude cyclones are low pressure areas which are capable of producing anything from cloudiness and mild snow storms to heavy blizzards. During a hemispheres fall and spring, the atmosphere over continents can be cold enough through the depth of the troposphere to cause snowfall, in the Northern Hemisphere, the northern side of the low pressure area produces the most snow. For the southern mid-latitudes, the side of a cyclone that produces the most snow is the southern side, a cold front, the leading edge of a cooler mass of air, can produce frontal snowsqualls—an intense frontal convective line, when temperature is near freezing at the surface.
The strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow. This type of snowsquall generally lasts less than 30 minutes at any point along its path, in cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder which is dubbed thundersnow. A warm front can produce snow for a period, as warm, moist air overrides below-freezing air, snow transitions to rain in the warm sector behind the front. The same effect occurs over bodies of salt water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the air mass is uplifted by the orographic influence of higher elevations on the downwind shores
Scandinavia /ˌskændᵻˈneɪviə/ is a historical and cultural region in Northern Europe characterized by a common ethnocultural North Germanic heritage and mutually intelligible North Germanic languages. The term Scandinavia always includes the three kingdoms of Denmark and Sweden, the remote Norwegian islands of Svalbard and Jan Mayen are usually not seen as a part of Scandinavia, nor is Greenland, an overseas territory of Denmark. This looser definition almost equates to that of the Nordic countries, in Nordic languages, only Denmark and Sweden are commonly included in the definition of Scandinavia. In English usage, Scandinavia sometimes refers to the geographical area, the name Scandinavia originally referred vaguely to the formerly Danish, now Swedish, region Scania. Icelanders and the Faroese are to a significant extent descended from the Norse, Finland is mainly populated by Finns, with a minority of approximately 5% of Swedish speakers. A small minority of Sami people live in the north of Scandinavia.
The Danish and Swedish languages form a continuum and are known as the Scandinavian languages—all of which are considered mutually intelligible with one another. Faroese and Icelandic, sometimes referred to as insular Scandinavian languages, are intelligible in continental Scandinavian languages only to a limited extent, Finnish and Meänkieli are closely related to each other and more distantly to the Sami languages, but are entirely unrelated to the Scandinavian languages. Apart from these, German and Romani are recognized minority languages in Scandinavia, the southern and by far most populous regions of Scandinavia have a temperate climate. Scandinavia extends north of the Arctic Circle, but has mild weather for its latitude due to the Gulf Stream. Much of the Scandinavian mountains have a tundra climate. There are many lakes and moraines, legacies of the last glacial period, Scandinavia usually refers to Denmark and Sweden. Some sources argue for the inclusion of the Faroe Islands and Iceland, though that broader region is known by the countries concerned as Norden.
Before this time, the term Scandinavia was familiar mainly to classical scholars through Pliny the Elders writings, and was used vaguely for Scania, as a political term, Scandinavia was first used by students agitating for Pan-Scandinavianism in the 1830s. After a visit to Sweden, Andersen became a supporter of early political Scandinavism, the term is often defined according to the conventions of the cultures that lay claim to the term in their own use. More precisely, and subject to no dispute, is that Finland is included in the broader term Nordic countries, various promotional agencies of the Nordic countries in the United States serve to promote market and tourism interests in the region. The official tourist boards of Scandinavia sometimes cooperate under one umbrella, Norways government entered one year later. All five Nordic governments participate in the joint promotional efforts in the United States through the Scandinavian Tourist Board of North America, Scandinavia can thus be considered a subset of the Nordic countries
The North Pole, known as the Geographic North Pole or Terrestrial North Pole, is defined as the point in the Northern Hemisphere where the Earths axis of rotation meets its surface. The North Pole is the northernmost point on the Earth, lying diametrically opposite the South Pole and it defines geodetic latitude 90° North, as well as the direction of true north. At the North Pole all directions point south, all lines of longitude converge there, along tight latitude circles, counterclockwise is east and clockwise is west. The North Pole is at the center of the Northern Hemisphere, while the South Pole lies on a continental land mass, the North Pole is located in the middle of the Arctic Ocean amid waters that are almost permanently covered with constantly shifting sea ice. This makes it impractical to construct a permanent station at the North Pole, the Soviet Union, and Russia, constructed a number of manned drifting stations on a generally annual basis since 1937, some of which have passed over or very close to the Pole.
Since 2002, the Russians have established a base, Barneo. This operates for a few weeks during early spring, studies in the 2000s predicted that the North Pole may become seasonally ice-free because of Arctic ice shrinkage, with timescales varying from 2016 to the late 21st century or later. The sea depth at the North Pole has been measured at 4,261 m by the Russian Mir submersible in 2007 and at 4,087 m by USS Nautilus in 1958. The nearest land is said to be Kaffeklubben Island, off the northern coast of Greenland about 700 km away. The nearest permanently inhabited place is Alert in the Qikiqtaaluk Region, Canada, around the beginning of the 20th century astronomers noticed a small apparent variation of latitude, as determined for a fixed point on Earth from the observation of stars. Part of this variation could be attributed to a wandering of the Pole across the Earths surface, the wandering has several periodic components and an irregular component. The component with a period of about 435 days is identified with the eight-month wandering predicted by Euler and is now called the Chandler wobble after its discoverer and it is desirable to tie the system of Earth coordinates to fixed landforms.
Of course, given plate tectonics and isostasy, there is no system in all geographic features are fixed. Yet the International Earth Rotation and Reference Systems Service and the International Astronomical Union have defined a framework called the International Terrestrial Reference System. As early as the 16th century, many eminent people correctly believed that the North Pole was in a sea and it was therefore hoped that passage could be found through ice floes at favorable times of the year. Several expeditions set out to find the way, generally with whaling ships, one of the earliest expeditions to set out with the explicit intention of reaching the North Pole was that of British naval officer William Edward Parry, who in 1827 reached latitude 82°45′ North. In 1871 the Polaris expedition, a US attempt on the Pole led by Charles Francis Hall, another British Royal Navy attempt on the pole, part of the British Arctic Expedition, by Commander Albert H. Markham reached a then-record 83°2026 North in May 1876 before turning back.
An 1879–1881 expedition commanded by US naval officer George W. DeLong ended tragically when their ship, over half the crew, including DeLong, were lost
Arctic ice pack
The Arctic ice pack is the ice cover of the Arctic Ocean and its vicinity. The Arctic ice pack undergoes a seasonal cycle in which ice melts in spring and summer, reaches a minimum around mid-September, increases during fall. Summer ice cover in the Arctic is about 50% of winter cover, some of the ice survives from one year to the next. Currently 28% of Arctic basin sea ice is ice, thicker than seasonal ice, up to 3–4 meters thick over large areas. As well as the seasonal cycle there has been an underlying trend of declining sea ice in the Arctic in recent decades. Sea ice has an important effect on the balance of the polar oceans, since it insulates the warm ocean from the much colder air above. Sea ice is highly reflective of solar radiation, reflecting about 60% of incoming solar radiation when bare and this is much greater than the reflectivity of the sea and thus the ice affects the absorption of sunlight at the surface. The sea ice cycle is an important source of dense bottom water, while freezing, water rejects its salt content, leaving pure ice.
The remaining surface water, made dense by the salinity, sinks. This production of water is a factor in maintaining the thermohaline circulation. In the Arctic, a key area where pancake ice forms the dominant ice type over a region is the so-called Odden ice tongue in the Greenland Sea. Most of the old ice continues south, driven by the wind, so an open water surface is exposed on which new ice forms as frazil. Reliable measurements of sea ice edge begin within the satellite era, from the late 1970s, the Scanning Multichannel Microwave Radiometer on Seasat and Nimbus 7 satellites provided information that was independent of solar illumination or meteorological conditions. The frequency and accuracy of passive microwave measurements improved with the launch of the DMSP F8 Special Sensor Microwave/Imager SSMI in 1987. Both the sea ice area and extent are estimated, with the latter being larger, the trends from 1979 to 2002 have been a statistically significant Arctic sea ice decrease of −2. 5% ±0. 9% per decade during those 23 years.
Climate models simulated this trend in 2002, the September minimum ice extent trend for 1979–2011 declined by 12. 0% per decade during 32 years. In 2007 the minimum extent fell by more than a million square kilometers, new research shows the Arctic Sea ice to be melting faster than predicted by any of the 18 computer models used by the Intergovernmental Panel on Climate Change in preparing its 2007 assessments. In 2012, a new low of about 3,500,000 km2 was reached
Alaska is a U. S. state located in the northwest extremity of North America. To the north are the Chukchi and Beaufort seas–the southern parts of the Arctic Ocean, the Pacific Ocean lies to the south and southwest. Alaska is the largest state in the United States by area, the 3rd least populous, approximately half of Alaskas residents live within the Anchorage metropolitan area. Alaskas economy is dominated by the fishing, natural gas, military bases and tourism are a significant part of the economy. The United States purchased Alaska from the Russian Empire on March 30,1867, the area went through several administrative changes before becoming organized as a territory on May 11,1912. It was admitted as the 49th state of the U. S. on January 3,1959, the name Alaska was introduced in the Russian colonial period when it was used to refer to the peninsula. It was derived from an Aleut, or Unangam idiom, which refers to the mainland of Alaska. Literally, it means object to which the action of the sea is directed, Alaska is the northernmost and westernmost state in the United States and has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere.
Alaska is the only non-contiguous U. S. state on continental North America and it is technically part of the continental U. S. but is sometimes not included in colloquial use, Alaska is not part of the contiguous U. S. often called the Lower 48. The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. Alaskas territorial waters touch Russias territorial waters in the Bering Strait, as the Russian Big Diomede Island, Alaska has a longer coastline than all the other U. S. states combined. Alaska is the largest state in the United States by total area at 663,268 square miles, over twice the size of Texas, Alaska is larger than all but 18 sovereign countries. Counting territorial waters, Alaska is larger than the area of the next three largest states, Texas and Montana. It is larger than the area of the 22 smallest U. S. states. Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the rest of the United States, as such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase.
The region is dominated by the Alexander Archipelago as well as the Tongass National Forest and it contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaskas largest city. The Alaska Marine Highway provides a vital transportation link throughout the area. The Interior is the largest region of Alaska, much of it is uninhabited wilderness, Fairbanks is the only large city in the region
Summer is the hottest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, the date of the beginning of summer varies according to climate and culture. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, a variable seasonal lag means that the meteorological center of the season, which is based on average temperature patterns, occurs several weeks after the time of maximal insolation. Under meteorological definitions, all seasons are set to start at the beginning of a calendar month. This meteorological definition of summer aligns with the commonly viewed notion of summer as the season with the longest days of the year, the meteorological reckoning of seasons is used in Australia, Denmark, the former Soviet Union and Japan. It is used by many in the United Kingdom, in Ireland, the summer months according to the national meteorological service, Met Éireann, are June and August.
However, according to the Irish Calendar, summer begins on 1 May, school textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June. Reckoning by hours of daylight alone, summer solstice marks the midpoint, not the beginning, midsummer takes place over the shortest night of the year, which is the summer solstice, or on a nearby date that varies with tradition. Where a seasonal lag of half a season or more is common, by this method, in North America, summer is the period from the summer solstice to the autumn equinox. The similar Canadian tradition starts summer on Victoria Day one week prior and ends, as in the United States, on Labour Day. In Chinese astronomy, summer starts on or around 5 May, with the known as lìxià, i. e. establishment of summer. In Australia and New Zealand, summer begins on 1 December. Summer is traditionally associated with hot or warm weather, in the Mediterranean regions, it is associated with dry weather, while in other places it is associated with rainy weather.
The wet season is the period of vegetation growth within the savanna climate regime. Where the wet season is associated with a shift in the prevailing winds. In the northern Atlantic Ocean, a tropical cyclone season occurs from 1 June to 30 November. The statistical peak of the Atlantic hurricane season is 10 September, the Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March, in the North Indian basin, storms are most common from April to December, with peaks in May and November
Sea ice arises as seawater freezes. Because ice is less dense water, it floats on the oceans surface. Sea ice covers about 7% of the Earth’s surface and about 12% of the world’s oceans. Much of the sea ice is enclosed within the polar ice packs in the Earths polar regions, the Arctic ice pack of the Arctic Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, due to the action of winds and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean, depending on location, sea ice expanses may incorporate icebergs. Sea ice does not simply grow and melt, during its lifespan, it is very dynamic. Due to the action of winds, water temperature. Sea ice is classified according to whether or not it is able to drift, Sea ice can be classified according to whether or not it is attached to the shoreline.
If attached, it is called landfast ice, or more often and unlike fast ice, drift ice occurs further offshore in very wide areas, and encompasses ice that is free to move with currents and winds. The physical boundary between fast ice and drift ice is the fast ice boundary, the drift ice zone may be further divided into a shear zone, a marginal ice zone and a central pack. Drift ice consists of floes, individual pieces of sea ice 20 metres or more across, the term pack ice is used either as a synonym to drift ice, or to designate drift ice zone in which the floes are densely packed. The overall sea ice cover is termed the ice canopy from the perspective of submarine navigation, another classification used by scientists to describe sea ice is based on age, that is, on its development stages. These stages are, new ice, young ice, first-year, new ice is a general term used for recently frozen sea water that does not yet make up solid ice. It may consist of ice, slush, or shuga. Other terms, such as ice and pancake ice, are used for ice crystal accumulations under the action of wind.
Nilas designates a sea ice crust up to 10 centimetres in thickness and it bends without breaking around waves and swells. Nilas can be subdivided into dark nilas – up to 5 centimetres in thickness and very dark
Tierra del Fuego
Tierra del Fuego is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the island, Isla Grande de Tierra del Fuego, with an area of 48,100 km2. Tierra del Fuego is divided between Chile and Argentina, with the controlling the eastern half of the main island. The southernmost extent of the archipelago is at about latitude 55 S, the earliest known human settlement in Tierra del Fuego dates to around 8,000 B. C. Europeans first explored the islands during Ferdinand Magellans expedition of 1520, Tierra del Fuego, petroleum extraction dominates economic activity in the north of Tierra del Fuego, while tourism and Antarctic logistics are important in the south. The earliest human settlement occurred around 8,000 B. C, the Yaghan were some of the earliest known humans to settle in Tierra del Fuego. Archeological sites with characteristics of their culture have found at locations such as Navarino Island. The name Tierra del Fuego derives from the Portuguese explorer Ferdinand Magellan, sailing for the Spanish Crown and he believed he was seeing the many fires of the Yaghan, which were visible from the sea, and that the Indians were waiting in the forests to ambush his armada.
In 1525 Francisco de Hoces was the first to speculate that Tierra del Fuego was one or more islands rather than part of what was called Terra Australis, francis Drake in 1578 and a Dutch VOC expedition in 1616 learned more about the geography. The latter expedition named Cape Horn, on his first voyage with the HMS Beagle in 1830, Robert FitzRoy picked up four native Fuegians, including Jemmy Button and brought them to England. The surviving three were taken to London to meet the King and Queen and were, for a time and they returned to Tierra del Fuego in the Beagle with FitzRoy and Charles Darwin, who made extensive notes about his visit to the islands. During the second half of the 19th century, the archipelago began to come under Chilean, both countries sought to claim the whole archipelago based on de jure Spanish colonial titles. Salesian Catholic missions were established in Río Grande and Dawson Island, anglican missions were established by British colonists at Keppel Island in the Falklands in 1855 and in 1870 at Ushuaia on the main island, which continued to operate through the 19th century.
Thomas Bridges learned the language and compiled a 30, 000-word Yaghan grammar and it was published in the 20th century and considered an important ethnological work. An 1879 Chilean expedition led by Ramón Serrano Montaner reported large amounts of gold in the streams. This prompted massive immigration to the island between 1883 and 1909. Numerous Argentines and Croatians settled in the main island, julius Popper, a Romanian explorer, was one of the most successful entrepreneurs in the region. Granted rights by the Argentine government to exploit any gold deposits he found in Tierra del Fuego, despite the missionaries efforts, many natives died
A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation, about one third of the land surface of the world is arid or semi-arid. This includes much of the regions where little precipitation occurs. Deserts can be classified by the amount of precipitation falls, by the temperature that prevails. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces, although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and this picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface, rocks are smoothed down, and the wind sorts sand into uniform deposits.
The grains end up as level sheets of sand or are piled high in billowing sand dunes, other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place, other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate, there may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur and animals living in the desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistant cuticles, some annual plants germinate and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture. Animals need to cool and find enough food and water to survive.
Many are nocturnal and stay in the shade or underground during the heat of the day and they tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine. Some animals remain in a state of dormancy for long periods and they reproduce rapidly while conditions are favorable before returning to dormancy. People have struggled to live in deserts and the surrounding lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available, the cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Many trade routes have been forged across deserts, especially across the Sahara Desert, large numbers of slaves were taken northwards across the Sahara
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, sleet, graupel, Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and precipitates. Thus and mist are not precipitation but suspensions, because the vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated, Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called showers, moisture that is lifted or otherwise forced to rise over a layer of sub-freezing air at the surface may be condensed into clouds and rain. This process is active when freezing rain is occurring. A stationary front is often present near the area of freezing rain, provided necessary and sufficient atmospheric moisture content, the moisture within the rising air will condense into clouds, namely stratus and cumulonimbus.
Eventually, the droplets will grow large enough to form raindrops. Lake-effect snowfall can be locally heavy, thundersnow is possible within a cyclones comma head and within lake effect precipitation bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation, on the leeward side of mountains, desert climates can exist due to the dry air caused by compressional heating. The movement of the trough, or intertropical convergence zone. Precipitation is a component of the water cycle, and is responsible for depositing the fresh water on the planet. Approximately 505,000 cubic kilometres of water falls as precipitation each year,398,000 cubic kilometres of it over the oceans and 107,000 cubic kilometres over land. Given the Earths surface area, that means the globally averaged annual precipitation is 990 millimetres, Climate classification systems such as the Köppen climate classification system use average annual rainfall to help differentiate between differing climate regimes.
Precipitation may occur on celestial bodies, e. g. when it gets cold, Mars has precipitation which most likely takes the form of frost. Precipitation is a component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km3 of water falls as precipitation each year,398,000 km3 of it over the oceans, given the Earths surface area, that means the globally averaged annual precipitation is 990 millimetres. Mechanisms of producing precipitation include convective and orographic rainfall, Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice
The Equator usually refers to an imaginary line on the Earths surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. The Equator is about 40,075 kilometres long, some 78. 7% lies across water and 21. 3% over land, other planets and astronomical bodies have equators similarly defined. Generally, an equator is the intersection of the surface of a sphere with the plane that is perpendicular to the spheres axis of rotation. The latitude of the Earths equator is by definition 0° of arc, the equator is the only line of latitude which is a great circle — that is, one whose plane passes through the center of the globe. The plane of Earths equator when projected outwards to the celestial sphere defines the celestial equator, in the cycle of Earths seasons, the plane of the equator passes through the Sun twice per year, at the March and September equinoxes. To an observer on the Earth, the Sun appears to travel North or South over the equator at these times, light rays from the center of the Sun are perpendicular to the surface of the Earth at the point of solar noon on the Equator.
Locations on the Equator experience the quickest sunrises and sunsets because the sun moves nearly perpendicular to the horizon for most of the year. The Earth bulges slightly at the Equator, the diameter of the Earth is 12,750 kilometres. Because the Earth spins to the east, spacecraft must launch to the east to take advantage of this Earth-boost of speed, seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earths axis relative to the plane of revolution. During the year the northern and southern hemispheres are inclined toward or away from the sun according to Earths position in its orbit, the hemisphere inclined toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter. At the equinoxes, the Earths axis is not tilted toward the sun, instead it is perpendicular to the sun meaning that the day is about 12 hours long, as is the night, across the whole of the Earth. Near the Equator there is distinction between summer, autumn, or spring.
The temperatures are usually high year-round—with the exception of high mountains in South America, the temperature at the Equator can plummet during rainstorms. In many tropical regions people identify two seasons, the wet season and the dry season, but many places close to the Equator are on the oceans or rainy throughout the year, the seasons can vary depending on elevation and proximity to an ocean. The Equator lies mostly on the three largest oceans, the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean. The highest point on the Equator is at the elevation of 4,690 metres, at 0°0′0″N 77°59′31″W and this is slightly above the snow line, and is the only place on the Equator where snow lies on the ground. At the Equator the snow line is around 1,000 metres lower than on Mount Everest, the Equator traverses the land of 11 countries, it passes through two island nations, though without making a landfall in either. Starting at the Prime Meridian and heading eastwards, the Equator passes through, Despite its name, its island of Annobón is 155 km south of the Equator, and the rest of the country lies to the north