Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to foreshortening , nearby objects show a larger parallax than farther objects, so parallax can be used to determine distances.
169-498: To measure large distances, such as the distance of a planet or a star from Earth , astronomers use the principle of parallax. Here, the term parallax is the semi-angle of inclination between two sight-lines to the star, as observed when Earth is on opposite sides of the Sun in its orbit. These distances form the lowest rung of what is called "the cosmic distance ladder ", the first in a succession of methods by which astronomers determine
338-583: A r c s e c ) . {\displaystyle d(\mathrm {pc} )=1/p(\mathrm {arcsec} ).} For example, the distance to Proxima Centauri is 1/0.7687 = 1.3009 parsecs (4.243 ly). On Earth, a coincidence rangefinder or parallax rangefinder can be used to find distance to a target. In surveying , the problem of resection explores angular measurements from a known baseline for determining an unknown point's coordinates. The most important fundamental distance measurements in astronomy come from trigonometric parallax, as applied in
507-475: A Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Proxima Centauri for this star on August 21, 2016, and it is now so included in the List of IAU approved Star Names. In 2016, a superflare was observed from Proxima Centauri, the strongest flare ever seen. The optical brightness increased by a factor of 68× to approximately magnitude 6.8. It
676-491: A circumstellar disk , and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides ). According to nebular theory , planetesimals formed by accretion , with the primordial Earth being estimated as likely taking anywhere from 70 to 100 million years to form. Estimates of the age of the Moon range from 4.5 Ga to significantly younger. A leading hypothesis
845-440: A graticule , not in actual contact with the display on an oscilloscope , etc. When viewed through a stereo viewer, aerial picture pair offers a pronounced stereo effect of landscape and buildings. High buildings appear to "keel over" in the direction away from the center of the photograph. Measurements of this parallax are used to deduce the height of the buildings, provided that flying height and baseline distances are known. This
1014-424: A moving group of stars, which would indicate a common point of origin, such as in a star cluster . As of 2022, three planets (one confirmed and two candidates) have been detected in orbit around Proxima Centauri, with one possibly being among the lightest ever detected by radial velocity ("d"), one close to Earth's size within the habitable zone ("b"), and a possible gas dwarf that orbits much further out than
1183-441: A boy". In a philosophic/geometric sense: an apparent change in the direction of an object, caused by a change in observational position that provides a new line of sight. The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view. In contemporary writing, parallax can also be the same story, or a similar story from approximately the same timeline, from one book, told from
1352-593: A closest approach distance of 2.90 ly (0.89 pc) in about 27,400 years, followed by a 2014 study by C. A. L. Bailer-Jones predicting a perihelion approach of 3.07 ly (0.94 pc) in roughly 26,710 years. Proxima Centauri is orbiting through the Milky Way at a distance from the Galactic Centre that varies from 27 to 31 kly (8.3 to 9.5 kpc ), with an orbital eccentricity of 0.07. Proxima Centauri has been suspected to be
1521-492: A common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common orbit around the Sun, the period of the synodic month , from new moon to new moon, is 29.53 days. Viewed from the celestial north pole , the motion of Earth, the Moon, and their axial rotations are all counterclockwise . Viewed from a vantage point above the Sun and Earth's north poles, Earth orbits in
1690-505: A compact emission source about 1.2 arcseconds from the star. There was a hint at an additional warm dust belt at a distance of 0.4 AU from the star. However, upon further analysis, these emissions were determined to be most likely the result of a large flare emitted by the star in March 2017. The presence of dust within 4 AU radius from the star is not needed to model the observations. Proxima Centauri b, or Alpha Centauri Cb, orbits
1859-537: A companion of the Alpha Centauri binary star system since its discovery in 1915. For this reason, it is sometimes referred to as Alpha Centauri C. Data from the Hipparcos satellite, combined with ground-based observations, were consistent with the hypothesis that the three stars are a gravitationally bound system. Kervella et al. (2017) used high-precision radial velocity measurements to determine with
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#17327762328092028-548: A counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic ), and the Earth-Moon plane is tilted up to ±5.1 degrees against the Earth–Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses . The Hill sphere , or
2197-691: A different perspective in another book. The word and concept feature prominently in James Joyce 's 1922 novel, Ulysses . Orson Scott Card also used the term when referring to Ender's Shadow as compared to Ender's Game . The metaphor is invoked by Slovenian philosopher Slavoj Žižek in his 2006 book The Parallax View , borrowing the concept of "parallax view" from the Japanese philosopher and literary critic Kojin Karatani . Žižek notes The philosophical twist to be added (to parallax), of course,
2366-420: A full rotation about its axis so that the Sun returns to the meridian . The orbital speed of Earth averages about 29.78 km/s (107,200 km/h; 66,600 mph), which is fast enough to travel a distance equal to Earth's diameter, about 12,742 km (7,918 mi), in seven minutes, and the distance from Earth to the Moon, 384,400 km (238,900 mi), in about 3.5 hours. The Moon and Earth orbit
2535-434: A full rotation once every 83.5 days. A subsequent time series analysis of chromospheric indicators in 2002 suggests a longer rotation period of 116.6 ± 0.7 days. Later observations of the star's magnetic field subsequently revealed that the star rotates with a period of 89.8 ± 4 days, consistent with a measurement of 92.1 +4.2 −3.5 days from radial velocity observations. Because of its low mass,
2704-421: A globe-spanning mid-ocean ridge system. At Earth's polar regions , the ocean surface is covered by seasonally variable amounts of sea ice that often connects with polar land, permafrost and ice sheets , forming polar ice caps . Earth's land covers 29.2%, or 149 million km (58 million sq mi) of Earth's surface. The land surface includes many islands around the globe, but most of
2873-484: A high degree of confidence that Proxima and Alpha Centauri are gravitationally bound. Proxima Centauri's orbital period around the Alpha Centauri ;AB barycenter is 547 000 +6600 −4000 years with an eccentricity of 0.5 ± 0.08 ; it approaches Alpha Centauri to 4300 +1100 −900 AU at periastron and retreats to 13 000 +300 −100 AU at apastron . At present, Proxima Centauri
3042-403: A higher level of uncertainty because the relative velocity of observed stars is an additional unknown. When applied to samples of multiple stars, the uncertainty can be reduced; the uncertainty is inversely proportional to the square root of the sample size. Moving cluster parallax is a technique where the motions of individual stars in a nearby star cluster can be used to find the distance to
3211-425: A liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation . Earth has a dynamic atmosphere , which sustains Earth's surface conditions and protects it from most meteoroids and UV-light at entry . It has a composition of primarily nitrogen and oxygen . Water vapor is widely present in the atmosphere, forming clouds that cover most of
3380-677: A parallax larger than a few times the precision of the measurement. In the 1990s, for example, the Hipparcos mission obtained parallaxes for over a hundred thousand stars with a precision of about a milliarcsecond , providing useful distances for stars out to a few hundred parsecs. The Hubble Space Telescope 's Wide Field Camera 3 has the potential to provide a precision of 20 to 40 micro arcseconds, enabling reliable distance measurements up to 5,000 parsecs (16,000 ly) for small numbers of stars. The Gaia space mission provided similarly accurate distances to most stars brighter than 15th magnitude. Distances can be measured within 10% as far as
3549-421: A period of roughly 442 days, which is shorter than the Sun's solar cycle of 11 years. Proxima Centauri has a relatively weak stellar wind , no more than 20% of the mass loss rate of the solar wind . Because the star is much smaller than the Sun, the mass loss per unit surface area from Proxima Centauri may be eight times that from the Sun's surface. A red dwarf with the mass of Proxima Centauri will remain on
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#17327762328093718-519: A planetary companion, it would be no less than 0.29 Earth masses. Further analysis confirmed the signal's existence leading up to the announcement of the candidate planet in February 2022. Prior to the discovery of Proxima Centauri b, the TV documentary Alien Worlds hypothesized that a life-sustaining planet could exist in orbit around Proxima Centauri or other red dwarfs. Such a planet would lie within
3887-408: A ruler marked on its top surface, the thickness of the ruler will separate its markings from the ticks. If viewed from a position not exactly perpendicular to the ruler, the apparent position will shift and the reading will be less accurate than the ruler is capable of. A similar error occurs when reading the position of a pointer against a scale in an instrument such as an analog multimeter . To help
4056-486: A team of astronomers using the Atacama Large Millimeter Array reported detecting a belt of cold dust orbiting Proxima Centauri at a range of 1−4 AU from the star. This dust has a temperature of around 40 K and has a total estimated mass of 1% of the planet Earth. They tentatively detected two additional features: a cold belt with a temperature of 10 K orbiting around 30 AU and
4225-577: A trip timescale of a century, inspiring several studies such as Project Orion , Project Daedalus , and Project Longshot . Project Breakthrough Starshot aims to reach the Alpha Centauri system within the first half of the 21st century, with microprobes travelling at 20% of the speed of light propelled by around 100 gigawatts of Earth-based lasers. The probes would perform a fly-by of Proxima Centauri about 20 years after its launch, or possibly go into orbit after about 140 years if swing-by 's around Proxima Centauri or Alpha Centauri are to be employed. Then
4394-576: Is 1.02 ± 0.08 mas . Because its distance is known, the actual diameter of Proxima Centauri can be calculated to be about 1/7 that of the Sun, or 1.5 times that of Jupiter . The star's mass, estimated from stellar theory, is 12.2% M ☉ , or 129 Jupiter masses ( M J ). The mass has been calculated directly, although with less precision, from observations of microlensing events to be 0.150 +0.062 −0.051 M ☉ . Lower mass main-sequence stars have higher mean density than higher mass ones, and Proxima Centauri
4563-514: Is rounded into an ellipsoid with a circumference of about 40,000 km. It is the densest planet in the Solar System . Of the four rocky planets , it is the largest and most massive. Earth is about eight light-minutes away from the Sun and orbits it , taking a year (about 365.25 days) to complete one revolution. Earth rotates around its own axis in slightly less than a day (in about 23 hours and 56 minutes). Earth's axis of rotation
4732-516: Is 12,947 ± 260 AU (1.94 ± 0.04 trillion km) from the Alpha Centauri AB barycenter, nearly to the furthest point in its orbit. Six single stars, two binary star systems, and a triple star share a common motion through space with Proxima Centauri and the Alpha Centauri system. (The co-moving stars include HD 4391 , γ Normae , and Gliese 676 .) The space velocities of these stars are all within 10 km/s of Alpha Centauri's peculiar motion . Thus, they may form
4901-493: Is 15.5. Its total luminosity over all wavelengths is only 0.16% that of the Sun, although when observed in the wavelengths of visible light to which the eye is most sensitive, it is only 0.0056% as luminous as the Sun. More than 85% of its radiated power is at infrared wavelengths. In 2002, optical interferometry with the Very Large Telescope (VLTI) found that the angular diameter of Proxima Centauri
5070-473: Is a red dwarf , because it belongs to the main sequence on the Hertzsprung–Russell diagram and is of spectral class M5.5 . The M5.5 class means that it falls in the low-mass end of M-type dwarf stars , with its hue shifted toward red-yellow by an effective temperature of ~3,000 K . Its absolute visual magnitude , or its visual magnitude as viewed from a distance of 10 parsecs (33 ly),
5239-456: Is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity . The thickness of the crust varies from about 6 kilometres (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as
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5408-399: Is a key component of the process of photogrammetry . Parallax error can be seen when taking photos with many types of cameras, such as twin-lens reflex cameras and those including viewfinders (such as rangefinder cameras ). In such cameras, the eye sees the subject through different optics (the viewfinder, or a second lens) than the one through which the photo is taken. As the viewfinder
5577-409: Is a red dwarf and a flare star, the planet's habitability is highly uncertain. A candidate super-Earth , Proxima Centauri c , roughly 1.5 AU (220 million km) away from Proxima Centauri, orbits it every 1,900 d (5.2 yr). A candidate sub-Earth , Proxima Centauri d , roughly 0.029 AU (4.3 million km) away, orbits it every 5.1 days. Proxima Centauri
5746-467: Is a special case of the principle of triangulation , which states that one can solve for all the sides and angles in a network of triangles if, in addition to all the angles in the network, the length of at least one side has been measured. Thus, the careful measurement of the length of one baseline can fix the scale of an entire triangulation network. In parallax, the triangle is extremely long and narrow, and by measuring both its shortest side (the motion of
5915-464: Is also an issue in image stitching , such as for panoramas. Parallax affects sighting devices of ranged weapons in many ways. On sights fitted on small arms and bows , etc., the perpendicular distance between the sight and the weapon's launch axis (e.g. the bore axis of a gun)—generally referred to as " sight height "—can induce significant aiming errors when shooting at close range, particularly when shooting at small targets. This parallax error
6084-453: Is always already inscribed into the perceived object itself, in the guise of its "blind spot," that which is "in the object more than the object itself," the point from which the object itself returns the gaze. "Sure the picture is in my eye, but I am also in the picture"... Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life . This
6253-535: Is approximately 9.8 m/s (32 ft/s ). Local differences in topography, geology, and deeper tectonic structure cause local and broad regional differences in Earth's gravitational field, known as gravity anomalies . The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from
6422-483: Is closer, with a parallax of 0.783″ ± 0.005″ . A size estimate for Proxima Centauri was obtained by the Canadian astronomer John Stanley Plaskett in 1925 using interferometry . The result was 207,000 miles (333,000 km), or approximately 0.24 R ☉ . In 1951, American astronomer Harlow Shapley announced that Proxima Centauri is a flare star . Examination of past photographic records showed that
6591-613: Is compensated for (when needed) via calculations that also take in other variables such as bullet drop , windage , and the distance at which the target is expected to be. Sight height can be used to advantage when "sighting in" rifles for field use. A typical hunting rifle (.222 with telescopic sights) sighted in at 75m will still be useful from 50 to 200 m (55 to 219 yd) without needing further adjustment. In some reticled optical instruments such as telescopes , microscopes or in telescopic sights ("scopes") used on small arms and theodolites , parallax can create problems when
6760-529: Is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms . During the Neoproterozoic , 1000 to 539 Ma , much of Earth might have been covered in ice. This hypothesis has been termed " Snowball Earth ", and it is of particular interest because it preceded the Cambrian explosion , when multicellular life forms significantly increased in complexity. Following
6929-455: Is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The internal mixing of its fuel by convection through its core and Proxima's relatively low energy-production rate, mean that it will be a main-sequence star for another four trillion years. Proxima Centauri has one known exoplanet and two candidate exoplanets: Proxima Centauri b ,
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7098-792: Is enabled by Earth being an ocean world , the only one in the Solar System sustaining liquid surface water . Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust . The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere . Most of Earth's land is at least somewhat humid and covered by vegetation , while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater , lakes, rivers and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates , which interact to produce mountain ranges, volcanoes , and earthquakes. Earth has
7267-460: Is estimated that similar flares occur around five times every year but are of such short duration, just a few minutes, that they have never been observed before. On 2020 April 22 and 23, the New Horizons spacecraft took images of two of the nearest stars, Proxima Centauri and Wolf 359 . When compared with Earth-based images, a very large parallax effect was easily visible. However, this
7436-449: Is exploited also in wiggle stereoscopy , computer graphics that provide depth cues through viewpoint-shifting animation rather than through binocular vision. Parallax arises due to a change in viewpoint occurring due to the motion of the observer, of the observed, or both. What is essential is relative motion. By observing parallax, measuring angles , and using geometry , one can determine distance . Distance measurement by parallax
7605-457: Is farthest out from its center of mass at its equatorial bulge, the summit of the volcano Chimborazo in Ecuador (6,384.4 km or 3,967.1 mi) is its farthest point out. Parallel to the rigid land topography the ocean exhibits a more dynamic topography . To measure the local variation of Earth's topography, geodesy employs an idealized Earth producing a geoid shape. Such a shape
7774-516: Is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds. The result is a smooth but irregular geoid surface, providing a mean sea level (MSL) as a reference level for topographic measurements. Earth's surface is the boundary between the atmosphere, and the solid Earth and oceans. Defined in this way, it has an area of about 510 million km (197 million sq mi). Earth can be divided into two hemispheres : by latitude into
7943-405: Is known as stereopsis . In computer vision the effect is used for computer stereo vision , and there is a device called a parallax rangefinder that uses it to find the range, and in some variations also altitude to a target. A simple everyday example of parallax can be seen in the dashboards of motor vehicles that use a needle-style mechanical speedometer . When viewed from directly in front,
8112-426: Is liquid under normal atmospheric pressure. Differences in the amount of captured energy between geographic regions (as with the equatorial region receiving more sunlight than the polar regions) drive atmospheric and ocean currents , producing a global climate system with different climate regions , and a range of weather phenomena such as precipitation , allowing components such as nitrogen to cycle . Earth
8281-438: Is no exception: it has a mean density of 47.1 × 10 kg/m (47.1 g/cm ), compared with the Sun's mean density of 1.411 × 10 kg/m (1.411 g/cm ). The measured surface gravity of Proxima Centauri, given as the base-10 logarithm of the acceleration in units of cgs , is 5.20. This is 162 times the surface gravity on Earth. A 1998 study of photometric variations indicates that Proxima Centauri completes
8450-513: Is now slightly longer than it was during the 19th century due to tidal deceleration , each day varies between 0 and 2 ms longer than the mean solar day. Earth's rotation period relative to the fixed stars , called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.0989 seconds of mean solar time ( UT1 ), or 23 56 4.0989 . Earth's rotation period relative to
8619-466: Is now travelling 17 km/s (38,000 mph) relative to the Sun, would reach Proxima Centauri in 73,775 years, were the spacecraft travelling in the direction of that star and Proxima was standing still. Proxima's actual galactic orbit means a slow-moving probe would have only several tens of thousands of years to catch the star at its closest approach, before it recedes out of reach. Nuclear pulse propulsion might enable such interstellar travel with
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#17327762328098788-408: Is often found above the lens of the camera, photos with parallax error are often slightly lower than intended, the classic example being the image of a person with their head cropped off. This problem is addressed in single-lens reflex cameras , in which the viewfinder sees through the same lens through which the photo is taken (with the aid of a movable mirror), thus avoiding parallax error. Parallax
8957-471: Is quite small, even for the nearest stars, measuring 1 arcsecond for an object at 1 parsec's distance (3.26 light-years ), and thereafter decreasing in angular amount as the distance increases. Astronomers usually express distances in units of parsecs (parallax arcseconds); light-years are used in popular media. Because parallax becomes smaller for a greater stellar distance, useful distances can be measured only for stars which are near enough to have
9126-622: Is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis , in which case its pronunciation is / ˈ ɡ aɪ . ə / rather than the more classical English / ˈ ɡ eɪ . ə / . There are a number of adjectives for the planet Earth. The word "earthly" is derived from "Earth". From the Latin Terra comes terran / ˈ t ɛr ə n / , terrestrial / t ə ˈ r ɛ s t r i ə l / , and (via French) terrene / t ə ˈ r iː n / , and from
9295-455: Is separated from Alpha Centauri by 2.18 degrees, or four times the angular diameter of the full Moon . Proxima Centauri has a relatively large proper motion—moving 3.85 arcseconds per year across the sky. It has a radial velocity towards the Sun of 22.2 km/s. From Proxima Centauri, the Sun would appear as a bright 0.4-magnitude star in the constellation Cassiopeia , similar to that of Achernar or Procyon from Earth . Among
9464-487: Is that it was formed by accretion from material loosed from Earth after a Mars -sized object with about 10% of Earth's mass, named Theia , collided with Earth. It hit Earth with a glancing blow and some of its mass merged with Earth. Between approximately 4.1 and 3.8 Ga , numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of
9633-483: Is that the observed distance is not simply "subjective", since the same object that exists "out there" is seen from two different stances or points of view. It is rather that, as Hegel would have put it, subject and object are inherently "mediated" so that an " epistemological " shift in the subject's point of view always reflects an " ontological " shift in the object itself. Or—to put it in Lacanese —the subject's gaze
9802-453: Is the basis for the astronomical unit (AU) and is equal to roughly 8.3 light minutes or 380 times Earth's distance to the Moon . Earth orbits the Sun every 365.2564 mean solar days , or one sidereal year . With an apparent movement of the Sun in Earth's sky at a rate of about 1°/day eastward, which is one apparent Sun or Moon diameter every 12 hours. Due to this motion, on average it takes 24 hours—a solar day—for Earth to complete
9971-457: Is tied to that of the Sun. Over the next 1.1 billion years , solar luminosity will increase by 10%, and over the next 3.5 billion years by 40%. Earth's increasing surface temperature will accelerate the inorganic carbon cycle , possibly reducing CO 2 concentration to levels lethally low for current plants ( 10 ppm for C4 photosynthesis ) in approximately 100–900 million years . A lack of vegetation would result in
10140-455: Is tilted with respect to the perpendicular to its orbital plane around the Sun, producing seasons . Earth is orbited by one permanent natural satellite , the Moon , which orbits Earth at 384,400 km (1.28 light seconds) and is roughly a quarter as wide as Earth. The Moon's gravity helps stabilize Earth's axis, causes tides and gradually slows Earth's rotation . Tidal locking has made
10309-447: Is too bright for a planet of its mass and age, implying that the planet may have a ring system with a radius of around 5 R J . A 2022 study disputed the radial velocity confirmation of the planet. In 2019, a team of astronomers revisited the data from ESPRESSO about Proxima Centauri b to refine its mass. While doing so, the team found another radial velocity spike with a periodicity of 5.15 days. They estimated that if it were
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#173277623280910478-466: The stellar parallax method . As the Earth orbits the Sun, the position of nearby stars will appear to shift slightly against the more distant background. These shifts are angles in an isosceles triangle , with 2 AU (the distance between the extreme positions of Earth's orbit around the Sun) making the base leg of the triangle and the distance to the star being the long equal-length legs. The amount of shift
10647-736: The Faint Object Spectrograph on board the Hubble Space Telescope appeared to show evidence of a companion orbiting at a distance of about 0.5 AU. A subsequent search using the Wide Field and Planetary Camera 2 failed to locate any companions. Astrometric measurements at the Cerro Tololo Inter-American Observatory appear to rule out a Jupiter -sized planet with an orbital period of 2−12 years. In 2017,
10816-522: The Galactic Center , about 30,000 light years away. Stars have a velocity relative to the Sun that causes proper motion (transverse across the sky) and radial velocity (motion toward or away from the Sun). The former is determined by plotting the changing position of the stars over many years, while the latter comes from measuring the Doppler shift of the star's spectrum caused by motion along
10985-527: The Milky Way and orbits about 28,000 light-years from its center. It is about 20 light-years above the galactic plane in the Orion Arm . The axial tilt of Earth is approximately 23.439281° with the axis of its orbit plane, always pointing towards the Celestial Poles . Due to Earth's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of
11154-759: The Pacific , North American , Eurasian , African , Antarctic , Indo-Australian , and South American . Other notable plates include the Arabian Plate , the Caribbean Plate , the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 Ma . The fastest-moving plates are
11323-477: The Rare Earth hypothesis , disagree that red dwarfs can sustain life. Any exoplanet in this star's habitable zone would likely be tidally locked, resulting in a relatively weak planetary magnetic moment , leading to strong atmospheric erosion by coronal mass ejections from Proxima Centauri. In December 2020, a candidate SETI radio signal BLC-1 was announced as potentially coming from the star. The signal
11492-419: The asthenosphere , the solid but less-viscous part of the upper mantle that can flow and move along with the plates. As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into
11661-415: The celestial equator , this is equivalent to an apparent diameter of the Sun or the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same. Earth orbits the Sun, making Earth the third-closest planet to the Sun and part of the inner Solar System . Earth's average orbital distance is about 150 million km (93 million mi), which
11830-534: The corona temperature of Proxima Centauri to 3.5 million K, compared to the 2 million K of the Sun's corona, and its total X-ray emission is comparable to the sun's. Proxima Centauri's overall activity level is considered low compared to other red dwarfs, which is consistent with the star's estimated age of 4.85 × 10 years, since the activity level of a red dwarf is expected to steadily wane over billions of years as its stellar rotation rate decreases. The activity level appears to vary with
11999-577: The exoplanet Proxima Centauri b were found in 2013 by Mikko Tuomi of the University of Hertfordshire from archival observation data. To confirm the possible discovery, a team of astronomers launched the Pale Red Dot project in January 2016. On August 24, 2016, the team of 31 scientists from all around the world, led by Guillem Anglada-Escudé of Queen Mary University of London , confirmed
12168-408: The ocean floor form the top of Earth's crust , which together with parts of the upper mantle form Earth's lithosphere . Earth's crust may be divided into oceanic and continental crust. Beneath the ocean-floor sediments, the oceanic crust is predominantly basaltic , while the continental crust may include lower density materials such as granite , sediments and metamorphic rocks. Nearly 75% of
12337-430: The precessing or moving mean March equinox (when the Sun is at 90° on the equator), is 86,164.0905 seconds of mean solar time (UT1) (23 56 4.0905 ) . Thus the sidereal day is shorter than the stellar day by about 8.4 ms. Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near
12506-413: The sphere of gravitational influence , of Earth is about 1.5 million km (930,000 mi) in radius. This is the maximum distance at which Earth's gravitational influence is stronger than that of the more distant Sun and planets. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun. Earth, along with the Solar System, is situated in
12675-464: The "last ice age", covered large parts of the continents, to the middle latitudes, in ice and ended about 11,700 years ago. Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose. The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen ( O 2 ) accumulated in
12844-473: The 'nearest [star] of Centaurus'. Proxima Centauri is a member of the Alpha Centauri star system , being identified as component Alpha Centauri C , and is 2.18° to the southwest of the Alpha Centauri AB pair. It is currently 12,950 AU (0.2 ly ) from AB, which it orbits with a period of about 550,000 years. Proxima Centauri is a red dwarf star with a mass about 12.5% of
13013-481: The Alpha Centauri pair continue to evolve and lose mass, Proxima Centauri is predicted to become unbound from the system in around 3.5 billion years from the present. Thereafter, the star will steadily diverge from the pair. Based on a parallax of 768.0665 ± 0.0499 mas , published in 2020 in Gaia Data Release 3 , Proxima Centauri is 4.2465 light-years (1.3020 pc ; 268,550 AU ) from
13182-484: The Cambrian explosion, 535 Ma , there have been at least five major mass extinctions and many minor ones. Apart from the proposed current Holocene extinction event, the most recent was 66 Ma , when an asteroid impact triggered the extinction of non-avian dinosaurs and other large reptiles, but largely spared small animals such as insects, mammals , lizards and birds. Mammalian life has diversified over
13351-473: The Dutch astronomer Joan Voûte measured the star's trigonometric parallax at 0.755 ″ ± 0.028 ″ and determined that Proxima Centauri was approximately the same distance from the Sun as Alpha Centauri. It was the lowest- luminosity star known at the time. An equally accurate parallax determination of Proxima Centauri was made by American astronomer Harold L. Alden in 1928, who confirmed Innes's view that it
13520-511: The ESO's HARPS instrument, indicating a possible additional planet orbiting Proxima Centauri. In 2020, the planet's existence was confirmed by Hubble astrometry data from c. 1995 . A possible direct imaging counterpart was detected in the infrared with the SPHERE , but the authors admit that they "did not obtain a clear detection." If their candidate source is in fact Proxima Centauri c, it
13689-654: The Earth. Terra is also the name of the planet in some Romance languages , languages that evolved from Latin , like Italian and Portuguese , while in other Romance languages the word gave rise to names with slightly altered spellings, like the Spanish Tierra and the French Terre . The Latinate form Gæa or Gaea ( English: / ˈ dʒ iː . ə / ) of the Greek poetic name Gaia ( Γαῖα ; Ancient Greek : [ɡâi̯.a] or [ɡâj.ja] )
13858-533: The Latin Tellus comes tellurian / t ɛ ˈ l ʊər i ə n / and telluric . The oldest material found in the Solar System is dated to 4.5682 +0.0002 −0.0004 Ga (billion years) ago. By 4.54 ± 0.04 Ga the primordial Earth had formed. The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into
14027-758: The Moon always face Earth with the same side. Earth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas and dust in the early Solar System . During the first billion years of Earth's history , the ocean formed and then life developed within it. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago in Africa and have spread across every continent on Earth. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted
14196-426: The Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic activity and outgassing . Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets , and comets . Sufficient water to fill the oceans may have been on Earth since it formed. In this model, atmospheric greenhouse gases kept the oceans from freezing when
14365-458: The Solar System's planetary-sized objects, Earth is the object with the highest density . Earth's mass is approximately 5.97 × 10 kg ( 5.970 Yg ). It is composed mostly of iron (32.1% by mass ), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to gravitational separation ,
14534-446: The Sun through space provides a longer baseline that will increase the accuracy of parallax measurements, known as secular parallax . For stars in the Milky Way disk, this corresponds to a mean baseline of 4 AU per year, while for halo stars the baseline is 40 AU per year. After several decades, the baseline can be orders of magnitude greater than the Earth–Sun baseline used for traditional parallax. However, secular parallax introduces
14703-403: The Sun when the star reaches its maximum radius, otherwise, with tidal effects, it may enter the Sun's atmosphere and be vaporized. Earth has a rounded shape , through hydrostatic equilibrium , with an average diameter of 12,742 kilometres (7,918 mi), making it the fifth largest planetary sized and largest terrestrial object of the Solar System . Due to Earth's rotation it has
14872-469: The Sun's mass ( M ☉ ), and average density about 33 times that of the Sun. Because of Proxima Centauri's proximity to Earth , its angular diameter can be measured directly. Its actual diameter is about one-seventh (14%) the diameter of the Sun. Although it has a very low average luminosity , Proxima Centauri is a flare star that randomly undergoes dramatic increases in brightness because of magnetic activity . The star's magnetic field
15041-710: The Sun. Previously published parallaxes include: 768.5 ± 0.2 mas in 2018 by Gaia DR2, 768.13 ± 1.04 mas , in 2014 by the Research Consortium On Nearby Stars ; 772.33 ± 2.42 mas , in the original Hipparcos Catalogue, in 1997; 771.64 ± 2.60 mas in the Hipparcos New Reduction, in 2007; and 768.77 ± 0.37 mas using the Hubble Space Telescope 's fine guidance sensors , in 1999. From Earth's vantage point, Proxima Centauri
15210-519: The X-ray emissions of smaller, solar-like flares were observed by the Japanese ASCA satellite in 1995. Proxima Centauri has since been the subject of study by most X-ray observatories, including XMM-Newton and Chandra . Because of Proxima Centauri's southern declination, it can only be viewed south of latitude 27° N . Red dwarfs such as Proxima Centauri are too faint to be seen with
15379-425: The atmosphere and due to interaction with ultraviolet solar radiation, formed a protective ozone layer ( O 3 ) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes . True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by
15548-434: The brightest ever detected, with a far ultraviolet emission of 2 × 10 erg . These flares can grow as large as the star and reach temperatures measured as high as 27 million K —hot enough to radiate X-rays . Proxima Centauri's quiescent X-ray luminosity, approximately (4–16) × 10 erg /s ((4–16) × 10 W ), is roughly equal to that of the much larger Sun. The peak X-ray luminosity of
15717-551: The candidate Proxima Centauri d and the disputed Proxima Centauri c . Proxima Centauri b orbits the star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.07 times that of Earth. Proxima b orbits within Proxima Centauri's habitable zone —the range where temperatures are right for liquid water to exist on its surface—but, because Proxima Centauri
15886-450: The center, the temperature may be up to 6,000 °C (10,830 °F), and the pressure could reach 360 GPa (52 million psi ). Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr , twice the present-day heat would have been produced, increasing
16055-597: The cluster. Only open clusters are near enough for this technique to be useful. In particular the distance obtained for the Hyades has historically been an important step in the distance ladder. Other individual objects can have fundamental distance estimates made for them under special circumstances. If the expansion of a gas cloud, like a supernova remnant or planetary nebula , can be observed over time, then an expansion parallax distance to that cloud can be estimated. Those measurements however suffer from uncertainties in
16224-454: The continental crust , particularly during the early stages of Earth's history. New continental crust forms as a result of plate tectonics , a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form supercontinents that have subsequently broken apart. At approximately 750 Ma , one of
16393-616: The continental surfaces are covered by sedimentary rocks, although they form about 5% of the mass of the crust. Earth's surface topography comprises both the topography of the ocean surface , and the shape of Earth's land surface. The submarine terrain of the ocean floor has an average bathymetric depth of 4 km, and is as varied as the terrain above sea level. Earth's surface is continually being shaped by internal plate tectonic processes including earthquakes and volcanism ; by weathering and erosion driven by ice, water, wind and temperature; and by biological processes including
16562-419: The core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago. The extent of Earth's magnetic field in space defines the magnetosphere . Ions and electrons of the solar wind are deflected by
16731-527: The core is primarily composed of the denser elements: iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements. The most common rock constituents of the crust are oxides . Over 99% of the crust is composed of various oxides of eleven elements, principally oxides containing silicon (the silicate minerals ), aluminium, iron, calcium, magnesium, potassium, or sodium. The major heat-producing isotopes within Earth are potassium-40 , uranium-238 , and thorium-232 . At
16900-463: The core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole . The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3.05 × 10 T , with a magnetic dipole moment of 7.79 × 10 Am at epoch 2000, decreasing nearly 6% per century (although it still remains stronger than its long time average). The convection movements in
17069-539: The days shorter. Above the Arctic Circle and below the Antarctic Circle there is no daylight at all for part of the year, causing a polar night , and this night extends for several months at the poles themselves. These same latitudes also experience a midnight sun , where the sun remains visible all day. By astronomical convention, the four seasons can be determined by the solstices—the points in
17238-462: The deviation of the object from sphericity. Binary stars which are both visual and spectroscopic binaries also can have their distance estimated by similar means, and do not suffer from the above geometric uncertainty. The common characteristic to these methods is that a measurement of angular motion is combined with a measurement of the absolute velocity (usually obtained via the Doppler effect ). The distance estimate comes from computing how far
17407-456: The distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder. Parallax also affects optical instruments such as rifle scopes, binoculars , microscopes , and twin-lens reflex cameras that view objects from slightly different angles. Many animals, along with humans, have two eyes with overlapping visual fields that use parallax to gain depth perception ; this process
17576-611: The earliest known supercontinents, Rodinia , began to break apart. The continents later recombined to form Pannotia at 600–540 Ma , then finally Pangaea , which also began to break apart at 180 Ma . The most recent pattern of ice ages began about 40 Ma , and then intensified during the Pleistocene about 3 Ma . High- and middle-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 21,000, 41,000 and 100,000 years. The Last Glacial Period , colloquially called
17745-544: The equally large area of land under permafrost ) or deserts (33%). The pedosphere is the outermost layer of Earth's land surface and is composed of soil and subject to soil formation processes. Soil is crucial for land to be arable. Earth's total arable land is 10.7% of the land surface, with 1.3% being permanent cropland. Earth has an estimated 16.7 million km (6.4 million sq mi) of cropland and 33.5 million km (12.9 million sq mi) of pastureland. The land surface and
17914-558: The existence of Proxima Centauri b through a peer-reviewed article published in Nature . The measurements were performed using two spectrographs: HARPS on the ESO 3.6 m Telescope at La Silla Observatory and UVES on the 8 m Very Large Telescope at Paranal Observatory . Several attempts to detect a transit of this planet across the face of Proxima Centauri have been made. A transit-like signal appearing on September 8, 2016,
18083-1114: The focus of the target image at varying distances into the same optical plane of the reticle (or vice versa). Many low-tier telescopic sights may have no parallax compensation because in practice they can still perform very acceptably without eliminating parallax shift. In this case, the scope is often set fixed at a designated parallax-free distance that best suits their intended usage. Typical standard factory parallax-free distances for hunting scopes are 100 yd (or 90 m) to make them suited for hunting shots that rarely exceed 300 yd/m. Some competition and military-style scopes without parallax compensation may be adjusted to be parallax free at ranges up to 300 yd/m to make them better suited for aiming at longer ranges. Scopes for guns with shorter practical ranges, such as airguns , rimfire rifles , shotguns , and muzzleloaders , will have parallax settings for shorter distances, commonly 50 m (55 yd) for rimfire scopes and 100 m (110 yd) for shotguns and muzzleloaders. Airgun scopes are very often found with adjustable parallax, usually in
18252-406: The form of an adjustable objective (or "AO" for short) design, and may adjust down to as near as 3 metres (3.3 yd). Non-magnifying reflector or "reflex" sights can be theoretically "parallax free". But since these sights use parallel collimated light this is only true when the target is at infinity. At finite distances, eye movement perpendicular to the device will cause parallax movement in
18421-638: The growth and decomposition of biomass into soil . Earth's mechanically rigid outer layer of Earth's crust and upper mantle , the lithosphere , is divided into tectonic plates . These plates are rigid segments that move relative to each other at one of three boundaries types: at convergent boundaries , two plates come together; at divergent boundaries , two plates are pulled apart; and at transform boundaries , two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity , mountain-building , and oceanic trench formation can occur. The tectonic plates ride on top of
18590-509: The habitable zone of Proxima Centauri, about 0.023–0.054 AU (3.4–8.1 million km) from the star, and would have an orbital period of 3.6–14 days. A planet orbiting within this zone may experience tidal locking to the star. If the orbital eccentricity of this hypothetical planet were low, Proxima Centauri would move little in the planet's sky, and most of the surface would experience either day or night perpetually. The presence of an atmosphere could serve to redistribute heat from
18759-404: The heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges . The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans. The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Near Earth's surface, gravitational acceleration
18928-447: The hydrogen fuel is exhausted, Proxima Centauri will then evolve into a helium white dwarf (without passing through the red giant phase) and steadily lose any remaining heat energy. The Alpha Centauri system may have formed through a low-mass star being dynamically captured by a more massive binary of 1.5–2 M ☉ within their embedded star cluster before the cluster dispersed. However, more accurate measurements of
19097-467: The inner two ("c"), although its status remains disputed. Searches for exoplanets around Proxima Centauri date to the late 1970s. In the 1990s, multiple measurements of Proxima Centauri's radial velocity constrained the maximum mass that a detectable companion could possess. The activity level of the star adds noise to the radial velocity measurements, complicating detection of a companion using this method. In 1998, an examination of Proxima Centauri using
19266-454: The interior of the star is completely convective , causing energy to be transferred to the exterior by the physical movement of plasma rather than through radiative processes . This convection means that the helium ash left over from the thermonuclear fusion of hydrogen does not accumulate at the core but is instead circulated throughout the star. Unlike the Sun, which will only burn through about 10% of its total hydrogen supply before leaving
19435-509: The known stars, Proxima Centauri has been the closest star to the Sun for about 32,000 years and will be so for about another 25,000 years, after which Alpha Centauri A and Alpha Centauri B will alternate approximately every 79.91 years as the closest star to the Sun. In 2001, J. García-Sánchez et al. predicted that Proxima Centauri will make its closest approach to the Sun in approximately 26,700 years, coming within 3.11 ly (0.95 pc). A 2010 study by V. V. Bobylev predicted
19604-406: The land surface is taken by the four continental landmasses , which are (in descending order): Africa-Eurasia , America (landmass) , Antarctica , and Australia (landmass) . These landmasses are further broken down and grouped into the continents . The terrain of the land surface varies greatly and consists of mountains, deserts , plains , plateaus , and other landforms . The elevation of
19773-513: The land surface varies from a low point of −418 m (−1,371 ft) at the Dead Sea , to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest . The mean height of land above sea level is about 797 m (2,615 ft). Land can be covered by surface water , snow, ice, artificial structures or vegetation. Most of Earth's land hosts vegetation, but considerable amounts of land are ice sheets (10%, not including
19942-453: The largest flares can reach 10 erg/s (10 W). Proxima Centauri's chromosphere is active, and its spectrum displays a strong emission line of singly ionized magnesium at a wavelength of 280 nm . About 88% of the surface of Proxima Centauri may be active, a percentage that is much higher than that of the Sun even at the peak of the solar cycle . Even during quiescent periods with few or no flares, this activity increases
20111-479: The line of sight. For a group of stars with the same spectral class and a similar magnitude range, a mean parallax can be derived from statistical analysis of the proper motions relative to their radial velocities. This statistical parallax method is useful for measuring the distances of bright stars beyond 50 parsecs and giant variable stars , including Cepheids and the RR Lyrae variables . The motion of
20280-399: The lithosphere, which is divided into independently moving tectonic plates. Beneath the lithosphere is the asthenosphere , a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath
20449-410: The loss of oxygen in the atmosphere, making current animal life impossible. Due to the increased luminosity, Earth's mean temperature may reach 100 °C (212 °F) in 1.5 billion years, and all ocean water will evaporate and be lost to space, which may trigger a runaway greenhouse effect , within an estimated 1.6 to 3 billion years. Even if the Sun were stable, a fraction of the water in
20618-456: The lowercase when it is preceded by "the", such as "the atmosphere of the earth". It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The name Terra / ˈ t ɛr ə / occasionally is used in scientific writing and especially in science fiction to distinguish humanity's inhabited planet from others, while in poetry Tellus / ˈ t ɛ l ə s / has been used to denote personification of
20787-497: The magnetosphere. During magnetic storms and substorms , charged particles can be deflected from the outer magnetosphere and especially the magnetotail, directed along field lines into Earth's ionosphere , where atmospheric atoms can be excited and ionized, causing an aurora . Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time ( 86,400.0025 SI seconds ). Because Earth's solar day
20956-409: The magnetosphere; solar wind pressure compresses the day-side of the magnetosphere, to about 10 Earth radii, and extends the night-side magnetosphere into a long tail. Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bow shock precedes the day-side magnetosphere within the solar wind. Charged particles are contained within
21125-483: The magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates. The ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field, and the Van Allen radiation belts are formed by high-energy particles whose motion is essentially random, but contained in
21294-419: The main sequence for about four trillion years. As the proportion of helium increases because of hydrogen fusion, the star will become smaller and hotter, gradually transforming into a so-called "blue dwarf" . Near the end of this period it will become significantly more luminous, reaching 2.5% of the Sun's luminosity ( L ☉ ) and warming any orbiting bodies for a period of several billion years. When
21463-467: The main sequence, Proxima Centauri will consume nearly all of its fuel before the fusion of hydrogen comes to an end. Convection is associated with the generation and persistence of a magnetic field . The magnetic energy from this field is released at the surface through stellar flares that briefly (as short as per ten seconds) increase the overall luminosity of the star. On May 6, 2019, a flare event bordering Solar M and X flare class , briefly became
21632-417: The mantle, an extremely low viscosity liquid outer core lies above a solid inner core . Earth's inner core may be rotating at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year, although both somewhat higher and much lower rates have also been proposed. The radius of the inner core is about one-fifth of that of Earth. The density increases with depth. Among
21801-612: The mantle. Due to this recycling, most of the ocean floor is less than 100 Ma old. The oldest oceanic crust is located in the Western Pacific and is estimated to be 200 Ma old. By comparison, the oldest dated continental crust is 4,030 Ma , although zircons have been found preserved as clasts within Eoarchean sedimentary rocks that give ages up to 4,400 Ma , indicating that at least some continental crust existed at that time. The seven major plates are
21970-548: The modern oceans will descend to the mantle , due to reduced steam venting from mid-ocean ridges. The Sun will evolve to become a red giant in about 5 billion years . Models predict that the Sun will expand to roughly 1 AU (150 million km; 93 million mi), about 250 times its present radius. Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will move to an orbit 1.7 AU (250 million km; 160 million mi) from
22139-399: The mother of Thor . Historically, "Earth" has been written in lowercase. Beginning with the use of Early Middle English , its definite sense as "the globe" was expressed as "the earth". By the era of Early Modern English , capitalization of nouns began to prevail , and the earth was also written the Earth , particularly when referenced along with other heavenly bodies. More recently,
22308-496: The naked eye. Even from Alpha Centauri A or B, Proxima would only be seen as a fifth magnitude star. It has apparent visual magnitude 11, so a telescope with an aperture of at least 8 cm (3.1 in) is needed to observe it, even under ideal viewing conditions—under clear, dark skies with Proxima Centauri well above the horizon. In 2016, the International Astronomical Union organized
22477-424: The name is sometimes simply given as Earth , by analogy with the names of the other planets , though "earth" and forms with "the earth" remain common. House styles now vary: Oxford spelling recognizes the lowercase form as the more common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name, such as a description of the "Earth's atmosphere", but employs
22646-425: The newly forming Sun had only 70% of its current luminosity . By 3.5 Ga , Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind . As the molten outer layer of Earth cooled it formed the first solid crust , which is thought to have been mafic in composition. The first continental crust , which was more felsic in composition, formed by
22815-408: The object must be to make its observed absolute velocity appear with the observed angular motion. Measurements made by viewing the position of some marker relative to something to be measured are subject to parallax error if the marker is some distance away from the object of measurement and not viewed from the correct position. For example, if measuring the distance between two ticks on a line with
22984-432: The observer) and the small top angle (always less than 1 arcsecond , leaving the other two close to 90 degrees), the length of the long sides (in practice considered to be equal) can be determined. In astronomy, assuming the angle is small, the distance to a star (measured in parsecs ) is the reciprocal of the parallax (measured in arcseconds ): d ( p c ) = 1 / p (
23153-593: The ocean may have covered Earth completely. The world ocean is commonly divided into the Pacific Ocean, Atlantic Ocean, Indian Ocean, Antarctic or Southern Ocean , and Arctic Ocean, from largest to smallest. The ocean covers Earth's oceanic crust , with the shelf seas covering the shelves of the continental crust to a lesser extent. The oceanic crust forms large oceanic basins with features like abyssal plains , seamounts , submarine volcanoes , oceanic trenches , submarine canyons , oceanic plateaus , and
23322-670: The oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/a (3.0 in/year) and the Pacific Plate moving 52–69 mm/a (2.0–2.7 in/year). At the other extreme, the slowest-moving plate is the South American Plate, progressing at a typical rate of 10.6 mm/a (0.42 in/year). Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical ( rheological ) properties. The outer layer
23491-599: The orbit of maximum axial tilt toward or away from the Sun—and the equinoxes , when Earth's rotational axis is aligned with its orbital axis. In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September. In the Southern Hemisphere, the situation is reversed, with
23660-649: The ozone layer, life colonized Earth's surface. Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia , biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland , and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia. The earliest direct evidence of life on Earth
23829-474: The partial melting of this mafic crust. The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggests that at least some felsic crust existed as early as 4.4 Ga , only 140 Ma after Earth's formation. There are two main models of how this initial small volume of continental crust evolved to reach its current abundance: (1) a relatively steady growth up to
23998-501: The past 66 Mys , and several million years ago, an African ape species gained the ability to stand upright. This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the evolution of humans . The development of agriculture , and then civilization , led to humans having an influence on Earth and the nature and quantity of other life forms that continues to this day. Earth's expected long-term future
24167-478: The planet's environment . Humanity's current impact on Earth's climate and biosphere is unsustainable , threatening the livelihood of humans and many other forms of life, and causing widespread extinctions . The Modern English word Earth developed, via Middle English , from an Old English noun most often spelled eorðe . It has cognates in every Germanic language , and their ancestral root has been reconstructed as * erþō . In its earliest attestation,
24336-400: The planet. The water vapor acts as a greenhouse gas and, together with other greenhouse gases in the atmosphere, particularly carbon dioxide (CO 2 ), creates the conditions for both liquid surface water and water vapor to persist via the capturing of energy from the Sun's light . This process maintains the current average surface temperature of 14.76 °C (58.57 °F), at which water
24505-421: The polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres. Most of Earth's surface is ocean water: 70.8% or 361 million km (139 million sq mi). This vast pool of salty water is often called the world ocean , and makes Earth with its dynamic hydrosphere a water world or ocean world . Indeed, in Earth's early history
24674-495: The present day, which is supported by the radiometric dating of continental crust globally and (2) an initial rapid growth in the volume of continental crust during the Archean , forming the bulk of the continental crust that now exists, which is supported by isotopic evidence from hafnium in zircons and neodymium in sedimentary rocks. The two models and the data that support them can be reconciled by large-scale recycling of
24843-433: The process by which the brain exploits the parallax due to the different views from the eye to gain depth perception and estimate distances to objects. Animals also use motion parallax , in which the animals (or just the head) move to gain different viewpoints. For example, pigeons (whose eyes do not have overlapping fields of view and thus cannot use stereopsis) bob their heads up and down to see depth. The motion parallax
25012-452: The radial velocity are needed to confirm this hypothesis. If Proxima Centauri was bound to the Alpha Centauri system during its formation, the stars are likely to share the same elemental composition. The gravitational influence of Proxima might have disturbed the Alpha Centauri protoplanetary disks . This would have increased the delivery of volatiles such as water to the dry inner regions, so possibly enriching any terrestrial planets in
25181-493: The rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today. The mean heat loss from Earth is 87 mW m , for a global heat loss of 4.42 × 10 W . A portion of the core's thermal energy is transported toward the crust by mantle plumes , a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts . More of
25350-415: The resultant apparent "floating" movements of the reticle over the target image when the user moves his/her head/eye laterally (up/down or left/right) behind the sight, i.e. an error where the reticle does not stay aligned with the user's optical axis . Some firearm scopes are equipped with a parallax compensation mechanism, which consists of a movable optical element that enables the optical system to shift
25519-564: The reticle image in exact relationship to the eye position in the cylindrical column of light created by the collimating optics. Firearm sights, such as some red dot sights , try to correct for this via not focusing the reticle at infinity, but instead at some finite distance, a designed target range where the reticle will show very little movement due to parallax. Some manufacturers market reflector sight models they call "parallax free", but this refers to an optical system that compensates for off axis spherical aberration , an optical error induced by
25688-460: The reticle is not coincident with the focal plane of the target image. This is because when the reticle and the target are not at the same focus, the optically corresponded distances being projected through the eyepiece are also different, and the user's eye will register the difference in parallaxes between the reticle and the target (whenever eye position changes) as a relative displacement on top of each other. The term parallax shift refers to
25857-522: The shape of an ellipsoid , bulging at its Equator ; its diameter is 43 kilometres (27 mi) longer there than at its poles . Earth's shape also has local topographic variations; the largest local variations, like the Mariana Trench (10,925 metres or 35,843 feet below local sea level), shortens Earth's average radius by 0.17% and Mount Everest (8,848 metres or 29,029 feet above local sea level) lengthens it by 0.14%. Since Earth's surface
26026-406: The speed may show exactly 60, but when viewed from the passenger seat, the needle may appear to show a slightly different speed due to the angle of viewing combined with the displacement of the needle from the plane of the numerical dial. Because the eyes of humans and other animals are in different positions on the head, they present different views simultaneously. This is the basis of stereopsis ,
26195-456: The spherical mirror used in the sight that can cause the reticle position to diverge off the sight's optical axis with change in eye position. Because of the positioning of field or naval artillery , each gun has a slightly different perspective of the target relative to the location of the fire-control system . When aiming guns at the target, the fire control system must compensate for parallax to assure that fire from each gun converges on
26364-492: The star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.07 times that of the Earth . Moreover, the equilibrium temperature of Proxima Centauri b is estimated to be within the range where water could exist as liquid on its surface; thus, placing it within the habitable zone of Proxima Centauri. The first indications of
26533-547: The star displayed a measurable increase in magnitude on about 8% of the images, making it the most active flare star then known. The proximity of the star allows for detailed observation of its flare activity. In 1980, the Einstein Observatory produced a detailed X-ray energy curve of a stellar flare on Proxima Centauri. Further observations of flare activity were made with the EXOSAT and ROSAT satellites , and
26702-457: The star's Earth, Proxima Centauri c would be equivalent to Neptune. Due to its large distance from Proxima Centauri, it is unlikely to be habitable, with a low equilibrium temperature of around 39 K. The planet was first reported by Italian astrophysicist Mario Damasso and his colleagues in April 2019. Damasso's team had noticed minor movements of Proxima Centauri in the radial velocity data from
26871-419: The star's flares could strip the atmosphere off any nearby planet. If the planet had a strong magnetic field, the field would deflect the particles from the atmosphere; even the slow rotation of a tidally locked planet that spins once for every time it orbits its star would be enough to generate a magnetic field, as long as part of the planet's interior remained molten. Other scientists, especially proponents of
27040-425: The star-lit side to the far side of the planet. Proxima Centauri's flare outbursts could erode the atmosphere of any planet in its habitable zone, but the documentary's scientists thought that this obstacle could be overcome. Gibor Basri of the University of California, Berkeley argued: "No one [has] found any showstoppers to habitability." For example, one concern was that the torrents of charged particles from
27209-460: The summer and winter solstices exchanged and the spring and autumnal equinox dates swapped. Proxima Centauri Proxima Centauri is the nearest star to Earth after the Sun , located 4.25 light-years away in the southern constellation of Centaurus . This object was discovered in 1915 by Robert Innes . It is a small, low-mass star , too faint to be seen with the naked eye , with an apparent magnitude of 11.13. Its Latin name means
27378-406: The system with this material. Alternatively, Proxima Centauri may have been captured at a later date during an encounter, resulting in a highly eccentric orbit that was then stabilized by the galactic tide and additional stellar encounters. Such a scenario may mean that Proxima Centauri's planetary companions have had a much lower chance for orbital disruption by Alpha Centauri. As the members of
27547-536: The target. Several of Mark Renn 's sculptural works play with parallax, appearing abstract until viewed from a specific angle. One such sculpture is The Darwin Gate (pictured) in Shrewsbury , England, which from a certain angle appears to form a dome, according to Historic England , in "the form of a Saxon helmet with a Norman window... inspired by features of St Mary's Church which was attended by Charles Darwin as
27716-411: The user avoid this problem, the scale is sometimes printed above a narrow strip of mirror , and the user's eye is positioned so that the pointer obscures its reflection, guaranteeing that the user's line of sight is perpendicular to the mirror and therefore to the scale. The same effect alters the speed read on a car's speedometer by a driver in front of it and a passenger off to the side, values read from
27885-461: The word eorðe was used to translate the many senses of Latin terra and Greek γῆ gē : the ground, its soil , dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra /Tellūs and Greek Gaia , Earth may have been a personified goddess in Germanic paganism : late Norse mythology included Jörð ("Earth"), a giantess often given as
28054-620: The year. This causes the seasonal change in climate, with summer in the Northern Hemisphere occurring when the Tropic of Cancer is facing the Sun, and in the Southern Hemisphere when the Tropic of Capricorn faces the Sun. In each instance, winter occurs simultaneously in the opposite hemisphere. During the summer, the day lasts longer, and the Sun climbs higher in the sky. In winter, the climate becomes cooler and
28223-703: Was later determined to be human-made radio interference. In 1915, the Scottish astronomer Robert Innes , director of the Union Observatory in Johannesburg , South Africa , discovered a star that had the same proper motion as Alpha Centauri . He suggested that it be named Proxima Centauri (actually Proxima Centaurus ). In 1917, at the Royal Observatory at the Cape of Good Hope ,
28392-428: Was only used for illustrative purposes and did not improve on previous distance measurements. Because of the star's proximity to Earth, Proxima Centauri has been proposed as a flyby destination for interstellar travel. If non-nuclear, conventional propulsion technologies are used, the flight of a spacecraft to Proxima Centauri and its planets would probably require thousands of years. For example, Voyager 1 , which
28561-755: Was tentatively identified, using the Bright Star Survey Telescope at the Zhongshan Station in Antarctica. In 2016, in a paper that helped to confirm Proxima Centauri b's existence, a second signal in the range of 60 to 500 days was detected. However, stellar activity and inadequate sampling causes its nature to remain unclear. Proxima Centauri c is a candidate super-Earth or gas dwarf about 7 Earth masses orbiting at roughly 1.5 astronomical units (220,000,000 km) every 1,900 days (5.2 yr). If Proxima Centauri b were
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