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40-560: Due to Earth's axial tilt of 23.439281°, there is a seasonal variation in the lengths of the day and night. There is also a seasonal variation in temperatures, which lags the variation in day and night. Conventionally, winter in the Northern Hemisphere is taken as the period from the December solstice (typically December 21 UTC ) to the March equinox (typically March 20 UTC), while summer

80-579: A Nobel Prize in 1946 for advancing this area of physics by two magnitudes of pressure (400 MPa to 40 GPa). The list of founding fathers of this field includes also the names of Harry George Drickamer , Tracy Hall , Francis P. Bundy , Leonid F. Vereschagin  [ ru ] , and Sergey M. Stishov  [ ru ] . It was by applying high pressure as well as high temperature to carbon that synthetic diamonds were first produced alongside many other interesting discoveries. Almost any material when subjected to high pressure will compact itself into

120-548: A counterclockwise pattern. Hurricanes and tropical storms (massive low-pressure systems) spin counterclockwise in the Northern Hemisphere. The shadow of a sundial moves clockwise on latitudes north of the subsolar point and anticlockwise to the south. During the day at these latitudes, the Sun tends to rise to its maximum at a southerly position. Between the Tropic of Cancer and the Equator,

160-399: A denser form, for example, quartz (also called silica or silicon dioxide ) will first adopt a denser form known as coesite , then upon application of even higher pressure, form stishovite . These two forms of silica were first discovered by high-pressure experimenters, but then found in nature at the site of a meteor impact. Chemical bonding is likely to change under high pressure, when

200-652: A mean value, with a period of 672 years, an idea known as trepidation of the equinoxes. Perhaps the first to realize this was incorrect (during historic time) was Ibn al-Shatir in the fourteenth century and the first to realize that the obliquity is decreasing at a relatively constant rate was Fracastoro in 1538. The first accurate, modern, western observations of the obliquity were probably those of Tycho Brahe from Denmark , about 1584, although observations by several others, including al-Ma'mun , al-Tusi , Purbach , Regiomontanus , and Walther , could have provided similar information. Earth 's axis remains tilted in

240-449: A period of several million years, long-term changes in Earth's orbit , and hence its obliquity, have been investigated. For the past 5 million years, Earth's obliquity has varied between 22°2′33″ and 24°30′16″ , with a mean period of 41,040 years. This cycle is a combination of precession and the largest term in the motion of the ecliptic . For the next 1 million years, the cycle will carry

280-415: Is quite variable over millions of years and may be in a chaotic state; it varies as much as 0° to 60° over some millions of years, depending on perturbations of the planets. Some authors dispute that Mars's obliquity is chaotic, and show that tidal dissipation and viscous core-mantle coupling are adequate for it to have reached a fully damped state, similar to Mercury and Venus. The occasional shifts in

320-548: Is taken as the period from the June solstice through to the September equinox (typically on 23 September UTC). The dates vary each year due to the difference between the calendar year and the astronomical year . Within the Northern Hemisphere, oceanic currents can change the weather patterns that affect many factors within the north coast. Such events include El Niño–Southern Oscillation . Trade winds blow from east to west just above

360-445: Is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane ; equivalently, it is the angle between its equatorial plane and orbital plane. It differs from orbital inclination . At an obliquity of 0 degrees, the two axes point in the same direction; that is, the rotational axis is perpendicular to the orbital plane. The rotational axis of Earth , for example,

400-498: Is the imaginary line that passes through both the North Pole and South Pole , whereas the Earth's orbital axis is the line perpendicular to the imaginary plane through which the Earth moves as it revolves around the Sun ; the Earth's obliquity or axial tilt is the angle between these two lines. Over the course of an orbital period , the obliquity usually does not change considerably, and

440-660: Is the obliquity and T is tropical centuries from B1900.0 to the date in question. From 1984, the Jet Propulsion Laboratory's DE series of computer-generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac . Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated: where hereafter T is Julian centuries from J2000.0 . JPL's fundamental ephemerides have been continually updated. For instance, according to IAU resolution in 2006 in favor of

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480-493: The Northern hemisphere when the north pole is directed toward the Sun. Variations in Earth's axial tilt can influence the seasons and is likely a factor in long-term climatic change (also see Milankovitch cycles ) . The exact angular value of the obliquity is found by observation of the motions of Earth and planets over many years. Astronomers produce new fundamental ephemerides as the accuracy of observation improves and as

520-410: The Northern temperate zone . The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather. Tropical regions (between the Tropic of Cancer and the Equator, 0° latitude) are generally hot all year round and tend to experience a rainy season during the summer months, and a dry season during

560-512: The last glacial period ended about 10,000 years ago. Earth is currently in an interglacial period of the Quaternary , called the Holocene . The glaciations that occurred during the glacial period covered many areas of the Northern Hemisphere. The Arctic is a region around the North Pole (90° latitude ). Its climate is characterized by cold winters and cool summers. Precipitation mostly comes in

600-426: The orientation of the axis remains the same relative to the background of stars . This causes one pole to be pointed more toward the Sun on one side of the orbit, and more away from the Sun on the other side—the cause of the seasons on Earth. There are two standard methods of specifying a planet's tilt. One way is based on the planet's north pole , defined in relation to the direction of Earth's north pole, and

640-534: The Northern Hemisphere compared to the Southern Hemisphere, making the Northern Hemisphere more suitable for deep-space observation, as it is not "blinded" by the Milky Way. As of 2015, the Northern Hemisphere is home to approximately 6.4 billion people, which is around 87.0% of the Earth's total human population of 7.3 billion people. Axial tilt In astronomy , axial tilt , also known as obliquity ,

680-620: The Northern Hemisphere, together with about two-thirds of Africa and a small part of South America . During the 2.5 million years of the Pleistocene , numerous cold phases called glacials ( Quaternary ice age ), or significant advances of continental ice sheets, in Europe and North America , occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials which lasted about 10,000–15,000 years. The last cold episode of

720-491: The P*V term in the free energy becomes comparable to the energies of typical chemical bonds – i.e. at around 100 GPa. Among the most striking changes are metallization of oxygen at 96 GPa (rendering oxygen a superconductor), and transition of sodium from a nearly-free-electron metal to a transparent insulator at ~200 GPa. At ultimately high compression, however, all materials will metallize . High-pressure experimentation has led to

760-490: The P03 astronomical model, the Astronomical Almanac for 2010 specifies: These expressions for the obliquity are intended for high precision over a relatively short time span, perhaps ± several centuries. Jacques Laskar computed an expression to order T good to 0.02″ over 1000 years and several arcseconds over 10,000 years. where here t is multiples of 10,000 Julian years from J2000.0 . These expressions are for

800-588: The Sun can be seen to the north, directly overhead, or to the south at noon, depending on the time of year. In the Southern Hemisphere, the midday Sun is predominantly in the north. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from the Southern Hemisphere. The North Pole faces away from the Galactic Center of the Milky Way . This results in the Milky Way being sparser and dimmer in

840-456: The Sun on a planet's equatorial bulge. Like Earth, all of the rocky planets show axial precession. If the precession rate were very fast the obliquity would actually remain fairly constant even as the orbital plane changes. The rate varies due to tidal dissipation and core - mantle interaction, among other things. When a planet's precession rate approaches certain values, orbital resonances may cause large changes in obliquity. The amplitude of

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880-541: The absence of the Moon, Earth's obliquity might not be quite so unstable; varying only by about 20–25°. To resolve this contradiction, diffusion rate of obliquity has been calculated, and it was found that it takes more than billions of years for Earth's obliquity to reach near 90°. The Moon's stabilizing effect will continue for less than two billion years. As the Moon continues to recede from Earth due to tidal acceleration , resonances may occur which will cause large oscillations of

920-433: The axial tilt of Mars have been suggested as an explanation for the appearance and disappearance of rivers and lakes over the course of the existence of Mars. A shift could cause a burst of methane into the atmosphere, causing warming, but then the methane would be destroyed and the climate would become arid again. The obliquities of the outer planets are considered relatively stable. The stellar obliquity ψ s , i.e.

960-520: The axial tilt of a star with respect to the orbital plane of one of its planets, has been determined for only a few systems. By 2012, 49 stars have had sky-projected spin-orbit misalignment λ has been observed, which serves as a lower limit to ψ s . Most of these measurements rely on the Rossiter–McLaughlin effect . Since the launch of space-based telescopes such as Kepler space telescope , it has been made possible to determine and estimate

1000-431: The contribution having one of the resonant rates is divided by the difference between the resonant rate and the precession rate, so it becomes large when the two are similar. Mercury and Venus have most likely been stabilized by the tidal dissipation of the Sun. Earth was stabilized by the Moon, as mentioned above, but before its formation , Earth, too, could have passed through times of instability. Mars 's obliquity

1040-487: The discovery of the types of minerals which are believed to exist in the deep mantle of the Earth, such as silicate perovskite , which is thought to make up half of the Earth's bulk, and post-perovskite , which occurs at the core-mantle boundary and explains many anomalies inferred for that region. Pressure "landmarks": typical pressures reached by large-volume presses are up to 30–40 GPa, pressures that can be generated inside diamond anvil cells are ~1000 GPa, pressure in

1080-653: The equator. The winds pull surface water with them, creating currents, which flow westward due to the Coriolis effect . The currents then bend to the right, heading north. At about 30 degrees north latitude, a different set of winds, the westerlies , push the currents back to the east, producing a closed clockwise loop. Its surface is 60.7% water, compared with 80.9% water in the case of the Southern Hemisphere , and it contains 67.3% of Earth's land. The continents of North America and mainland Eurasia are located entirely in

1120-630: The form of snow. Areas inside the Arctic Circle (66°34′ latitude) experience some days in summer when the Sun never sets, and some days during the winter when it never rises. The duration of these phases varies from one day for locations right on the Arctic Circle to several months near the Pole, which is the middle of the Northern Hemisphere. Between the Arctic Circle and the Tropic of Cancer (23°26′ latitude) lies

1160-607: The obliquities of exoplanets in the habitable zone around low-mass stars tend to be eroded in less than 10 years, which means that they would not have tilt-induced seasons as Earth has. High pressure In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell , which can create high pressure . High pressure usually means pressures of thousands (kilo bars ) or millions (megabars) of times atmospheric pressure (about 1 bar or 100,000 Pa). Percy Williams Bridgman received

1200-534: The obliquity between 22°13′44″ and 24°20′50″ . The Moon has a stabilizing effect on Earth's obliquity. Frequency map analysis conducted in 1993 suggested that, in the absence of the Moon, the obliquity could change rapidly due to orbital resonances and chaotic behavior of the Solar System , reaching as high as 90° in as little as a few million years ( also see Orbit of the Moon ). However, more recent numerical simulations made in 2011 indicated that even in

1240-450: The obliquity of an extrasolar planet. The rotational flattening of the planet and the entourage of moons and/or rings, which are traceable with high-precision photometry provide access to planetary obliquity, ψ p . Many extrasolar planets have since had their obliquity determined, such as Kepler-186f and Kepler-413b . Astrophysicists have applied tidal theories to predict the obliquity of extrasolar planets . It has been shown that

Northern Hemisphere - Misplaced Pages Continue

1280-473: The obliquity. All four of the innermost, rocky planets of the Solar System may have had large variations of their obliquity in the past. Since obliquity is the angle between the axis of rotation and the direction perpendicular to the orbital plane, it changes as the orbital plane changes due to the influence of other planets. But the axis of rotation can also move ( axial precession ), due to torque exerted by

1320-500: The other way is based on the planet's positive pole , defined by the right-hand rule : Earth 's orbital plane is known as the ecliptic plane, and Earth's tilt is known to astronomers as the obliquity of the ecliptic , being the angle between the ecliptic and the celestial equator on the celestial sphere . It is denoted by the Greek letter Epsilon ε . Earth currently has an axial tilt of about 23.44°. This value remains about

1360-425: The same direction with reference to the background stars throughout a year (regardless of where it is in its orbit ) due to the gyroscope effect . This means that one pole (and the associated hemisphere of Earth ) will be directed away from the Sun at one side of the orbit, and half an orbit later (half a year later) this pole will be directed towards the Sun. This is the cause of Earth's seasons . Summer occurs in

1400-507: The same relative to a stationary orbital plane throughout the cycles of axial precession . But the ecliptic (i.e., Earth's orbit) moves due to planetary perturbations , and the obliquity of the ecliptic is not a fixed quantity. At present, it is decreasing at a rate of about 46.8″ per century (see details in Short term below) . The ancient Greeks had good measurements of the obliquity since about 350 BCE, when Pytheas of Marseilles measured

1440-557: The shadow of a gnomon at the summer solstice. About 830 CE, the Caliph Al-Mamun of Baghdad directed his astronomers to measure the obliquity, and the result was used in the Arab world for many years. In 1437, Ulugh Beg determined the Earth's axial tilt as 23°30′17″ (23.5047°). During the Middle Ages , it was widely believed that both precession and Earth's obliquity oscillated around

1480-464: The so-called mean obliquity, that is, the obliquity free from short-term variations. Periodic motions of the Moon and of Earth in its orbit cause much smaller (9.2 arcseconds ) short-period (about 18.6 years) oscillations of the rotation axis of Earth, known as nutation , which add a periodic component to Earth's obliquity. The true or instantaneous obliquity includes this nutation. Using numerical methods to simulate Solar System behavior over

1520-426: The understanding of the dynamics increases, and from these ephemerides various astronomical values, including the obliquity, are derived. Annual almanacs are published listing the derived values and methods of use. Until 1983, the Astronomical Almanac 's angular value of the mean obliquity for any date was calculated based on the work of Newcomb , who analyzed positions of the planets until about 1895: where ε

1560-447: The weather patterns that affect many factors within the north coast. For the same reason, flows of air down toward the northern surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the Northern Hemisphere. Conversely, air rising from the northern surface of the Earth (creating a region of low pressure) tends to draw air toward it in

1600-480: The winter months. In the Northern Hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the Coriolis effect . As a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres . These are best seen in ocean circulation patterns in the North Atlantic and North Pacific oceans. Within the Northern Hemisphere, oceanic currents can change

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