Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning,[1] at the start of the Sun path. The term can also refer to the entire process of the solar disk crossing the horizon.
Although the Sun appears to "rise" from the horizon, it is actually the Earth's motion that causes the Sun to appear. The illusion of a moving Sun results from Earth observers being in a rotating reference frame; this apparent motion caused many cultures to have mythologies and religions built around the geocentric model, which prevailed until astronomer Nicolaus Copernicus formulated his heliocentric model in the 16th century.[2]
Architect Buckminster Fuller proposed the terms "sunsight" and "sunclipse" to better represent the heliocentric model, though the terms have not entered into common language.[3][4]
Astronomically, sunrise occurs for only an instant, namely the moment at which the upper limb of the Sun appears tangent to the horizon.[1] However, the term sunrise commonly refers to periods of time both before and after this point:
The stage of sunrise known as false sunrise actually occurs before the Sun truly reaches the horizon because Earth's atmosphere refracts the Sun's image. At the horizon, the average amount of refraction is 34 arcminutes, though this amount varies based on atmospheric conditions.[1]
Also, unlike most other solar measurements, sunrise occurs when the Sun's upper limb, rather than its center, appears to cross the horizon. The apparent radius of the Sun at the horizon is 16 arcminutes.[1]
These two angles combine to define sunrise to occur when the Sun's center is 50 arcminutes below the horizon, or 90.83° from the zenith.[1]
The timing of sunrise varies throughout the year and is also affected by the viewer's latitude and longitude, altitude, and time zone. These changes are driven by the axial tilt of Earth, daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun, and the Earth and Moon's paired revolutions around each other. The analemma can be used to make approximate predictions of the time of sunrise.
In late winter and spring, sunrise as seen from temperate latitudes occurs earlier each day, reaching its earliest time shortly before the summer solstice; although the exact date varies by latitude. After this point, the time of sunrise gets later each day, reaching its latest shortly after the winter solstice, also varying by latitude. The offset between the dates of the solstice and the earliest or latest sunrise time is caused by the eccentricity of Earth's orbit and the tilt of its axis, and is described by the analemma, which can be used to predict the dates.
Variations in atmospheric refraction can alter the time of sunrise by changing its apparent position. Near the poles, the time-of-day variation is extreme, since the Sun crosses the horizon at a very shallow angle and thus rises more slowly.[1]
Accounting for atmospheric refraction and measuring from the leading edge slightly increases the average duration of day relative to night. The sunrise equation, however, which is used to derive the time of sunrise and sunset, uses the Sun's physical center for calculation, neglecting atmospheric refraction and the non-zero angle subtended by the solar disc.
Neglecting the effects of refraction and the Sun's non-zero size, whenever sunrise occurs, in temperate regions it is always in the northeast quadrant from the March equinox to the September equinox and in the southeast quadrant from the September equinox to the March equinox.[6] Sunrises occur approximately due east on the March and September equinoxes for all viewers on Earth.[7] Exact calculations of the azimuths of sunrise on other dates are complex, but they can be estimated with reasonable accuracy by using the analemma.
The figure on the right is calculated using the solar geometry routine in Ref.[8] as follows:
An interesting feature in the figure on the right is apparent hemispheric symmetry in regions where daily sunrise and sunset actually occur.
This symmetry becomes clear if the hemispheric relation in to the sunrise equation is applied to the x- and y-components of the solar vector presented in Ref.[8]
Air molecules and airborne particles scatter white sunlight as it passes through the Earth's atmosphere. This is done by a combination of Rayleigh scattering and Mie scattering.[9]
As a ray of white sunlight travels through the atmosphere to an observer, some of the colors are scattered out of the beam by air molecules and airborne particles, changing the final color of the beam the viewer sees. Because the shorter wavelength components, such as blue and green, scatter more strongly, these colors are preferentially removed from the beam.[9]
At sunrise and sunset, when the path through the atmosphere is longer, the blue and green components are removed almost completely, leaving the longer-wavelength orange and red hues seen at those times. The remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange.[10] The removal of the shorter wavelengths of light is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light (less than 50 nm in diameter).[11][12] The scattering by cloud droplets and other particles with diameters comparable to or larger than the sunlight's wavelengths (more than 600 nm) is due to Mie scattering and is not strongly wavelength-dependent. Mie scattering is responsible for the light scattered by clouds, and also for the daytime halo of white light around the Sun (forward scattering of white light).[13][14][15]
Sunset colors are typically more brilliant than sunrise colors, because the evening air contains more particles than morning air.[9][10][12][15] Ash from volcanic eruptions, trapped within the troposphere, tends to mute sunset and sunrise colors, while volcanic ejecta that is instead lofted into the stratosphere (as thin clouds of tiny sulfuric acid droplets), can yield beautiful post-sunset colors called afterglows and pre-sunrise glows. A number of eruptions, including those of Mount Pinatubo in 1991 and Krakatoa in 1883, have produced sufficiently high stratospheric sulfuric acid clouds to yield remarkable sunset afterglows (and pre-sunrise glows) around the world. The high altitude clouds serve to reflect strongly reddened sunlight still striking the stratosphere after sunset, down to the surface.
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| Arabian Desert ٱلصَّحْرَاء ٱلْعَرَبِيَّة |
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Desert near Sharjah, United Arab Emirates
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Map of the Arabian Desert ecoregion
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| Ecology | |
| Realm | Palearctic |
| Biome | deserts and xeric shrublands |
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| Geography | |
| Area | 1,855,470[1] km2 (716,400 mi2) |
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| Conservation | |
| Conservation status | critical/endangered[2] |
| Protected | 4.368%[1] |
The Arabian Desert (Arabic: ٱلصَّحْرَاء ٱلْعَرَبِيَّة) is a vast desert wilderness in West Asia that occupies almost the entire Arabian Peninsula with an area of 2,330,000 square kilometers (900,000 sq mi).[3] It stretches from Yemen to the Persian Gulf and Oman to Jordan and Iraq. It is the fourth largest desert in the world and the largest in Asia. At its center is Ar-Rub' al-Khali (The Empty Quarter), one of the largest continuous bodies of sand in the world. It is an extension of the Sahara Desert.[4]
Gazelles, oryx, sand cats, and spiny-tailed lizards are just some of the desert-adapted species that survive in this extreme environment, which features everything from red dunes to deadly quicksand. The climate is mostly dry (the major part receives around 100 mm (3.9 in) of rain per year, but some very rare places receive as little as 50 mm), and temperatures oscillate between very high heat and seasonal night time freezes. It is part of the deserts and xeric shrublands biome and lie in biogeographical realms of the Palearctic (northern part) and Afrotropical (southern part).
The Arabian Desert ecoregion has little biodiversity, although a few endemic plants grow here. Many species, such as the striped hyena, jackal and honey badger, have died out as a result of hunting, habitat destruction, overgrazing by livestock, off-road driving, and human encroachment on their habitat. Other species, such as the Arabian sand gazelle, have been successfully re-introduced and are protected at reserves.
The desert lies mostly in Saudi Arabia and covers most of the country. It extends into neighboring southern Iraq, southern Jordan, central Qatar, most of the Abu Dhabi emirate in the United Arab Emirates, western Oman, and northeastern Yemen. The ecoregion also includes most of the Sinai Peninsula in Egypt and the adjacent Negev desert in southern Israel.[1]
The Rub' al-Khali desert is a sedimentary basin stretching along a south-west to north-east axis across the Arabian Shelf.[5] At an altitude of 1,000 metres (3,300 ft), rock landscapes yield to the Rub' al-Khali, a vast stretch of sand whose extreme southern point crosses the center of Yemen. The sand overlies gravel or gypsum plains and the dunes reach maximum heights of up to 250 m (820 ft). The sands are predominantly silicates, composed of 80 to 90% quartz and the remainder feldspar, whose iron oxide-coated grains color the sands orange, purple, and red.
A corridor of sandy terrain known as the Ad-Dahna desert connects the An-Nafud desert (65,000 km2 or 40,389 square miles) in the north of Saudi Arabia to the Rub' al-Khali in the south-east.[citation needed] The Tuwaiq escarpment is an 800 km (500 mi) arc that includes limestone cliffs, plateaus, and canyons.[citation needed] There are brackish salt flats, including the quicksands of Umm al Samim.[2] The Sharqiya Sands, formerly known as Wahiba Sands of Oman are an isolated sand sea bordering the east coast.[6][7]
The Arabian Desert has a subtropical, hot desert climate, similar to the climate of the Sahara Desert (the world's largest hot desert). The Arabian Desert is actually an extension of the Sahara Desert over the Arabian peninsula.
The climate is mainly dry. Most areas get around 100 mm (3.9 in) of rain per year. Unlike the Sahara Desert—more than half of which is hyperarid (having rainfall of less than 50 mm (2.0 in) per year)—the Arabian Desert has only a few hyperarid areas. These rare driest areas may get only 30 to 40 mm (1.6 in) of rain per year.
The Arabian Desert’s sunshine duration index is very high by global standards: between 2,900 hours (66.2% of daylight hours) and 3,600 hours (82.1% of daylight hours), but typically around 3,400 hours (77.6% of daylight hours). Thus clear-sky conditions with plenty of sunshine prevail over the region throughout the year, and cloudy periods are infrequent. Visibility at ground level is relatively low, despite the brightness of the sun and moon, because of dust and humidity.
Temperatures remain high year round. In the summer, in low-lying areas, average high temperatures are generally over 40 °C (104 °F). In extremely low-lying areas, especially along the Persian Gulf (near sea level), summer temperatures can reach 48 °C (118 °F). Average low temperatures in summer are typically over 20 °C (68 °F) and in the south can sometimes exceed 30 °C (86 °F). Record high temperatures above 50 °C (122 °F) have been reached in many areas of the desert, partly because its overall elevation is relatively low. [citation needed]
The Arabian Desert ecoregion has about 900 species of plants.[8] The Rub'al-Khali has very limited floristic diversity. There are only 37 plant species, 20 recorded in the main body of the sands and 17 around the outer margins. Of these 37 species, one or two are endemic. Vegetation is very diffuse but fairly evenly distributed, with some interruptions of near sterile dunes.[2] Some typical plants are Calligonum crinitum on dune slopes, Cornulaca arabica (saltbush), Salsola stocksii (saltbush), and Cyperus conglomeratus. Other widespread species are Dipterygium glaucum, Limeum arabicum, and Zygophyllum mandavillei. Very few trees are found except at the outer margin (typically Acacia ehrenbergiana and Prosopis cineraria). Other species are a woody perennial Calligonum comosum, and annual herbs such as Danthonia forskallii.[2]
There are 102 native species of mammals.[8] Native mammals include the Arabian oryx (Oryx leucoryx), sand gazelle (Gazella marica), mountain gazelle (G. gazella), Nubian ibex (Capra nubiana), Arabian wolf (Canis lupus arabs), striped hyaena (Hyaena hyaena), caracal (Caracal caracal), sand cat (Felis margarita), red fox (Vulpes vulpes), and Cape hare (Lepus capensis).[2] The Asiatic cheetah[9] and Asiatic lion[10] used to live in the Arabian Desert. The ecoregion is home to 310 bird species.[8]
The area is home to several different cultures, languages, and peoples, with Islam as the predominant faith. The major ethnic group in the region is the Arabs, whose primary language is Arabic.
In the center of the desert lies Riyadh, the capital of Saudi Arabia, with more than 7 million inhabitants.[11] Other large cities, such as Dubai, Abu Dhabi, or Kuwait City, lie on the coast of the Persian Gulf.
Natural resources available in the Arabian Desert include oil, natural gas, phosphates, and sulfur.[citation needed]
Threats to the ecoregion include overgrazing by livestock and feral camels and goats, wildlife poaching, and damage to vegetation by off-road driving.[2]
The conservation status of the desert is critical/endangered. In the UAE, the sand gazelle and Arabian oryx are threatened, and honey badgers, jackals, and striped hyaenas already extirpated.[2]
4.37% of the ecoregion is in protected areas.[1]
Saudi Arabia has established a system of reserves overseen by the National Commission for Wildlife Conservation and Development (NCWCD).[2]
Protected areas in the United Arab Emirates include Al Houbara Protected Area (2492.0 km2), Al Ghadha Protected Area (1087.51 km2), Arabian Oryx Protected Area (5974.47 km2), Ramlah Protected Area (544.44 km2), and Al Beda'a Protected Area (417.0 km2).[12]
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Hot Air Balloon Dubai is a sunrise experience where guests fly over the Arabian Desert in a licensed hot air balloon, enjoying panoramic views and wildlife sightings.
Yes, Hot Air Balloon Dubai is very popular with couples and is ideal for romantic experiences and proposals.
No prior experience is needed to enjoy a Hot Air Balloon Dubai flight.
