Outer space (often simply called space) is the void that exists beyond any celestial body Astronomical objects are significant naturally occurring physical entities, associations or structures which current science has demonstrated to exist in outer space. The term astronomical object is sometimes used interchangeably with astronomical body. Typically an astronomical body refers to a single, cohesive structure that is bound together by including the Earth.^[1] It is not completely empty (i.e. a perfect vacuum In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". Even putting aside the complexities of the quantum vacuum, the classical notion of a perfect vacuum with gaseous pressure of exactly), but contains a low density of particles, predominantly hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its plasma In physics and chemistry, plasma is a gas in which a certain portion of the particles are ionized. The presence of a non-negligible number of charge carriers makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma, therefore, has properties quite unlike those of solids, liquids, or gases and is, as well as electromagnetic radiation Electromagnetic radiation is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to, magnetic fields Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field, and neutrinos Like the cosmic microwave background radiation , the CνB is a relic of the big bang, and while the CMB dates from when the universe was 380,000 years old, the CνB decoupled from matter when the universe was 2 seconds old. It is estimated that today the CνB has a temperature of roughly 1.95 K. Since low-energy neutrinos interact only very weakly. Theoretically, it also contains dark matter In astronomy and cosmology, dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation. Its existence was hypothesized to account for discrepancies between measurements of the mass of galaxies, clusters of galaxies and and dark energy In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Dark energy is the most popular way to explain recent observations and experiments that the universe appears to be expanding at an accelerating rate. In the.

Discovery

In 350 BC, Greek philosopher Aristotle Aristotle (384 BC – 322 BC) was a Greek philosopher, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, politics, government, ethics, biology, and zoology. Together with Plato and Socrates (Plato's teacher), Aristotle is one of the most suggested that nature abhors a vacuum, a principle that became known as the horror vacui. Based on this idea that a vacuum could not exist, it was widely held for many centuries that space could not be empty.^[2] As late as the seventeenth century, the French philosopher René Descartes René Descartes , (31 March 1596 – 11 February 1650), also known as Renatus Cartesius (Latinized form; adjectival form: "Cartesian"), was a French philosopher, mathematician, physicist, and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the "Father of Modern Philosophy", and much of argued that the entirety of space must be filled.^[3] It became known to Galileo Galilei Galileo Galilei was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations, and support for Copernicanism. Galileo has been called the "father of modern observational astronomy," that air had weight and so was subject to gravity. He also demonstrated that there was an established force that resisted the formation of a vacuum. However, it would remain for his pupil Evangelista Torricelli Evangelista Torricelli ( pronunciation ; October 15, 1608 – October 25, 1647) was an Italian physicist and mathematician, best known for his invention of the barometer to create an apparatus that would produce a vacuum. At the time this experiment created a scientific sensation in Europe. The French mathematician Blaise Pascal Blaise Pascal was a French mathematician, physicist, and Catholic philosopher. He was a child prodigy who was educated by his father, a Tax Collector in Rouen. Pascal's earliest work was in the natural and applied sciences where he made important contributions to the construction of mechanical calculators, the study of fluids, and clarified the reasoned that if the column of mercury was suspended by air then the column ought to be shorter at higher altitude. His brother in law, Florin Périer, repeated the experiment on the Puy-de-Dôme Puy-de-Dôme is a large lava dome and one of the youngest volcanoes in the Chaîne des Puys region of Massif Central in south-central France. Curiously, this chain of volcanoes including numerous cinder cones, lava domes, and maars is located far from the edge of any tectonic plate. Puy-de-Dôme is located approximately 10 km away from Clermont- mountain in central France and found that the column was shorter by three inches. This decrease in pressure was further demonstrated by carrying a half-full balloon up a mountain and watching it gradually inflate, then deflate upon descent. These and other experiments were used to overthrow the principle of horror vacui.^[4]

Further work on the physics of the vacuum was performed by Otto von Guericke Otto von Guericke (November 20, 1602 – May 11, 1686 (Julian calendar); November 30, 1602 – May 21, 1686 (Gregorian calendar) was a German scientist, inventor, and politician. His major scientific achievement was the establishment of the physics of vacuums. He correctly noted that the atmosphere of the Earth surrounds the planet like a shell, with the density gradually declining with altitude. He concluded that there must be a vacuum between the Earth and the Moon.^[5]

Early speculations as to the infinite dimension of space was performed in the sixteenth century by the Italian philosopher Giordano Bruno Giordano Bruno , born Filippo Bruno, was an Italian Dominican friar, philosopher, mathematician and astronomer, who is best known as a proponent of the infinity of the universe. His cosmological theories went beyond the Copernican model in identifying the sun as just one of an infinite number of independently moving heavenly bodies: he is the. He extended the Copernican heliocentric cosmology to the concept of an infinite universe that is filled with a substance he called aether According to ancient and medieval science, aether , also spelled æther or ether, is the material that fills the region of the Universe above the terrestrial sphere, which did not cause resistance to the motions of heavenly bodies.^[6] English philosopher William Gilbert arrived at a similar conclusion, arguing that the stars are visible to us only because they are surrounded by a thin aether or a void.^[7] This concept of an aether originated with ancient Greek Ancient Greece is the civilization belonging to the period of Greek history lasting from the Archaic period of the 8th to 6th centuries BC to 146 BC and the Roman conquest of Greece after the Battle of Corinth. At the center of this time period is Classical Greece, which flourished during the 5th to 4th centuries BC, at first under Athenian philosophers, including Aristotle, who conceived of it as the medium through which the heavenly bodies moved.^[8]

The concept of a universe filled with a luminiferous aether In the late 19th century, "luminiferous aether" , meaning light-bearing aether, was the term used to describe a medium for the propagation of light. The word aether stems via Latin from the Greek αιθήρ, from a root meaning to kindle, burn, or shine. It signifies the substance which was thought in ancient times to contain the remained in vogue among some scientists up until the twentieth century. This form of aether was viewed as the medium through which light could propagate. In 1887, the Michelson-Morley experiment The Michelson–Morley experiment was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University. Its results are generally considered to be the first strong evidence against the theory of a luminiferous aether. The experiment has also been referred to as "the kicking-off point for the theoretical was carried out as an attempt to detect the Earth's motion through this medium by looking for changes in the speed of light The speed of light, usually denoted by c, is a physical constant important in many areas of physics. Light and all other electromagnetic radiation always travel at this speed in empty space , regardless of the motion of the source or the inertial frame of the observer. Its value is exactly 299,792,458 metres per second (approximately 186,282 miles based on the direction of the planet's motion. However, the null result Generally, a null result is a result which is null : that is, the proposed result is absent. In science, it is an experimental outcome which does not show an otherwise expected effect. This does not imply a result of zero or nothing, simply a result that does not support the hypothesis. The term is a translation of the scientific Latin nullus indicated something was wrong with the concept. Since then the idea of the luminiferous aether had essentially been abandoned, to be replaced by Albert Einstein Albert Einstein (pronounced /ˈælbərt ˈaɪnstaɪn/; German: [ˈalbɐt ˈaɪnʃtaɪn] ; 14 March 1879 – 18 April 1955) was a theoretical physicist, philosopher and author who is widely regarded as one of the most influential and best known scientists and intellectuals of all time. A German-Swiss Nobel laureate, he is often regarded as the's theory of special relativity Special relativity (also known as the special theory of relativity or STR) is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein (after the considerable and independent contributions of Hendrik Lorentz, Henri Poincaré and others) in the paper "On the Electrodynamics of Moving Bodies". The latter held that the speed of light is a constant in a vacuum, regardless of the observer's motion or frame of reference A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer. It may also refer to both an observational reference frame and an attached.^[9][10]

The first professional astronomer to support the concept of an infinite universe was the Englishman Thomas Digges Sir Thomas Digges was an English mathematician and astronomer, and the first to exposit the Copernican system in English in 1576.^[11] However, the true scale of the universe remained unknown until the first successful measurement of the distance to a nearby star was performed in 1838 by the German astronomer Friedrich Bessel Friedrich Wilhelm Bessel was a German mathematician, astronomer, and systematizer of the Bessel functions (which were discovered by Daniel Bernoulli). He was a contemporary of Carl Gauss, also a mathematician and astronomer. The asteroid 1552 Bessel was named in his honour. He showed that the star 61 Cygni 61 Cygni,[note 1] sometimes called Bessel's Star or Piazzi's Flying Star, is a binary star system in the constellation Cygnus. It consists of a pair of K-type dwarf stars that orbit each other in a period of about 659 years, forming a visual binary. At fifth and sixth apparent magnitudes, they are among the least conspicuous stars visible in the had a parallax Parallax is an apparent displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration". Nearby objects have a larger parallax than of just 0.31 arcseconds A minute of arc, or arcminute or minute of angle , is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. This conversion is recognised for calculations involving SI Units. Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 minute of arc is 1/21,600 of the amount of arc in a closed circle. It is (compared to the modern value of 0.287″). This corresponded to a distance of over 10 light years A light-year, also light year or lightyear, is a unit of length, equal to just under 10 trillion kilometres (1016 metres, 10 petametres or 6 trillion miles). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in a vacuum in one Julian year.^[12] The distance scale to the Andromeda galaxy The Andromeda Galaxy is a spiral galaxy approximately 2,500,000 light-years away in the constellation Andromeda. It is also known as Messier 31, M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to our own, the Milky Way. As it is visible as a faint smudge on a moonless was determined in 1923 by American astronomer Edwin Hubble Edwin Powell Hubble was an American astronomer who profoundly changed our understanding of the universe by demonstrating the existence of galaxies other than our own, the Milky Way. He also discovered that the degree of "Doppler shift" (specifically "redshift") observed in the light spectra from other galaxies increased in when he measured the brightness of cepheid variables A Cepheid is a member of a class of pulsating variable stars. The relationship between a Cepheid variable's luminosity and pulsation period is quite precise, securing Cepheids as viable standard candles and the foundation of the Extragalactic Distance Scale within that galaxy. This established that the Andromeda galaxy, and by extension all galaxies, lay well outside the Milky Way The Milky Way Galaxy, commonly referred to as just the Milky Way, or sometimes simply as the Galaxy, is the galaxy in which the Solar System is located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. It is one of billions of galaxies in the observable universe. Its name is a translation of the Latin Via Lactea,.^[13]

The modern concept of outer space is based upon the Big Bang The Big Bang theory is the prevailing cosmological theory of the early development of the universe. The theory postulates that the Big Bang event took place at some finite time in the past: according to the best available measurements as of 2009[update], around 13.7 billion years ago. According to the Big Bang model, the universe, originally in an cosmology Cosmology , in strict usage, refers to the study of the Universe in its totality as it now is (or at least as it can be observed now), and by extension, humanity's place in it. Though the word cosmology is recent (first used in 1730 in Christian Wolff's Cosmologia Generalis), study of the universe has a long history involving science, philosophy,, which was first proposed in 1931 by the Belgian physicist Georges Lemaître Monsignor Georges Henri Joseph Édouard Lemaître ( lemaitre.ogg July 17, 1894 – June 20, 1966) was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer at the Catholic University of Leuven. He sometimes used the title Abbé or Monseigneur. This theory holds that the observable universe originated from a very compact form that has since undergone continuous expansion Hubble's law describes the observation in physical cosmology that the velocity at which various galaxies are receding from the earth is proportional to their distance from us. The law was first formulated by Edwin Hubble in 1929 after nearly a decade of observations. The recession velocity of the objects was inferred from their redshifts, many. Matter that remained following the initial expansion has since undergone gravitational collapse to create stars A star is a massive, luminous ball of plasma held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun. Historically, the most prominent stars on the celestial sphere were grouped together into constellations, galaxies A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy and other astronomical objects Astronomical objects are significant naturally occurring physical entities, associations or structures which current science has demonstrated to exist in outer space. The term astronomical object is sometimes used interchangeably with astronomical body. Typically an astronomical body refers to a single, cohesive structure that is bound together by, leaving behind a deep vacuum that forms what is now called outer space.^[14]

The term outer space was first recorded by the English Traditionally Christianity, mostly Anglicanism, but also non-conformists and also Roman Catholics (see Catholic Emancipation). Agnostics, atheist as well as other religions. (see Religion in England) poet Lady Emmeline Stuart-Wortley Lady Emmeline Stuart-Wortley née Manners was an English poet, best known for her Travels in the United States, etc. During 1849 and 1850. She was a daughter of the 5th Duke of Rutland and on 17 February 1831, she married Hon. Charles Stuart-Wortley-Mackenzie, a son of the 1st Baron Wharncliffe in her poem "The Maiden of Moscow" in 1842,^[15] and later popularised in the writings of HG Wells Herbert George Wells was an English author, now best known for his work in the science fiction genre. He was also a prolific writer in many other genres, including contemporary novels, history, politics and social commentary. Together with Jules Verne, Wells has been referred to as "The Father of Science Fiction" in 1901.^[16] The shorter term space is actually older, first used to mean the region beyond Earth's sky in John Milton John Milton was an English poet, polemicist, and civil servant for the Commonwealth of England. He is best known for his epic poem Paradise Lost's Paradise Lost Paradise Lost is an epic poem in blank verse by the 17th-century English poet John Milton. It was originally published in 1667 in ten books, with a total of over ten thousand individual lines of verse. A second edition followed in 1674, redivided into twelve books with minor revisions throughout and a note on the versification; the majority of the in 1667.^[17]

Environment

Outer space is the closest natural approximation of a perfect vacuum In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". Even putting aside the complexities of the quantum vacuum, the classical notion of a perfect vacuum with gaseous pressure of exactly. It has effectively no friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, or material elements sliding against each other. It may be thought of as the opposite of "slipperiness", allowing stars, planets and moons to move freely along ideal gravitational trajectories. However, even in the deep vacuum of intergalactic space there are still a few hydrogen atoms per cubic meter.^[18] By comparison, the air we breathe contains about 10²⁵ molecules per cubic meter.^[19] The sparse density of matter in outer space means that electromagnetic radiation can travel great distances without being scattered; the mean free path for a photon in intergalactic space is about 10²³ km, or 10 billion light years.^[20] The deep vacuum of space could make it an attractive environment for certain industrial processes, for instance those that require ultraclean surfaces.^[21]

Stars, planets, asteroids and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 1 Pa at 100 kilometres (62 mi) of altitude. This is known as the Kármán line, a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar wind, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre.

Temperature

All of the observable Universe is filled with photons that were created during the Big Bang, which is known as the cosmic microwave background radiation (CMB). There is quite likely a correspondingly large number of neutrinos called the cosmic neutrino background. The current black body temperature of this photon radiation is about 3 K (−270 °C; −454 °F). Some regions of outer space can contain highly energetic particles that have a much higher temperature than the CMB.

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