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150-426: It successfully carried science and technology experiments for about 5.7 years that have revealed a broad and detailed collection of space environmental data. LDEF's 69 months in space provided scientific data on the long-term effects of space exposure on materials, components and systems that has benefited NASA spacecraft designers to this day. Researchers identified the potential of the planned Space Shuttle to deliver

300-414: A DNA mutation from space exposure could yield a poisonous fruit. While incorrect, the report served to raise awareness of the experiment and generate discussion. Space seeds germinated sooner and grew faster than the control seeds. Space seeds were more porous than terrestrial seeds. At LDEF's launch, retrieval was scheduled for March 19, 1985, eleven months after deployment. Schedules slipped, postponing

450-489: A conjunction of Jupiter and Mars in 1106 or 1107 as evidence. The Persian astronomer Nasir al-Din al-Tusi (1201–1274) in his Tadhkira wrote: "The Milky Way, i.e. the Galaxy, is made up of a very large number of small, tightly clustered stars, which, on account of their concentration and smallness, seem to be cloudy patches. Because of this, it was likened to milk in color." Ibn Qayyim al-Jawziyya (1292–1350) proposed that

600-640: A dark matter area, also containing some visible stars, may extend up to a diameter of almost 2 million light-years (613 kpc). The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster , which is itself a component of the Laniakea Supercluster . It is estimated to contain 100–400 billion stars and at least that number of planets . The Solar System

750-666: A radius of about 39.5 kpc (130,000 ly), over twice as much as was determined in earlier studies, suggesting that about 90% of the mass of the galaxy is dark matter . In September 2023, astronomers reported that the virial mass of the Milky Way Galaxy is only 2.06 10 solar masses , only a 10th of the mass of previous studies. The mass was determined from data of the Gaia spacecraft . The Milky Way contains between 100 and 400 billion stars and at least that many planets. An exact figure would depend on counting

900-424: A spacecraft must travel faster than a sub-orbital spaceflight along an arcing trajectory . The energy required to reach Earth orbital velocity at an altitude of 600 km (370 mi) is about 36  MJ /kg, which is six times the energy needed merely to climb to the corresponding altitude. The escape velocity required to pull free of Earth's gravitational field altogether and move into interplanetary space

1050-619: A 2016 study. Such Earth-sized planets may be more numerous than gas giants, though harder to detect at great distances given their small size. Besides exoplanets, " exocomets ", comets beyond the Solar System, have also been detected and may be common in the Milky Way. More recently, in November 2020, over 300 million habitable exoplanets are estimated to exist in the Milky Way Galaxy. When compared to other more distant galaxies in

1200-471: A density of one proton per four cubic meters. The density of the universe is clearly not uniform; it ranges from relatively high density in galaxies—including very high density in structures within galaxies, such as planets, stars, and black holes —to conditions in vast voids that have much lower density, at least in terms of visible matter. Unlike matter and dark matter, dark energy seems not to be concentrated in galaxies: although dark energy may account for

1350-460: A great deal of detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but very prominent when viewed from rural areas when the Moon is below the horizon. Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of

1500-532: A hazard to astronauts, even in low Earth orbit. They create aurorae seen at high latitudes in an oval surrounding the geomagnetic poles . xGeo space is a concept used by the US to refer to space of high Earth orbits , ranging from beyond geosynchronous orbit (GEO) at approximately 35,786 km (22,236 mi), out to the L2 Earth-Moon Lagrange point at 448,900 km (278,934 mi). This

1650-406: A hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye . The Milky Way is a barred spiral galaxy with a D 25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years ), but only about 1,000 light-years thick at the spiral arms (more at the bulge). Recent simulations suggest that

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1800-647: A magnetic tape recorder that was powered by a lithium sulfur dioxide battery, e.g. , the Advanced Photovoltaic Experiment (S0014), which recorded data once a day, the German Solar cell study (S1002), and the Space Environment Effects on Fiber Optics Systems (M004). Six of the seven active experiments that needed to record data used one or two Experiment Power and Data System (EPDS) modules. Each EPDS contained

1950-455: A majority of the mass-energy in the universe, dark energy's influence is 5 orders of magnitude smaller than the influence of gravity from matter and dark matter within the Milky Way. Outer space is the closest known approximation to a perfect vacuum . It has effectively no friction , allowing stars, planets , and moons to move freely along their ideal orbits , following the initial formation stage. The deep vacuum of intergalactic space

2100-474: A measurement of the radial velocity of halo stars found that the mass enclosed within 80 kilo parsecs is 7 × 10   M ☉ . In a 2014 study, the mass of the entire Milky Way is estimated to be 8.5 × 10   M ☉ , but this is only half the mass of the Andromeda Galaxy. A recent 2019 mass estimate for the Milky Way is 1.29 × 10   M ☉ . Much of the mass of

2250-478: A payload to space, leave it there for a long-term exposure to the harsh outer space environment, and retrieve it for analysis on a separate mission. The LDEF concept evolved from a spacecraft proposed by NASA's Langley Research Center in 1970 to study the meteoroid environment, the Meteoroid and Exposure Module (MEM). The project was approved in 1974 and LDEF was built at NASA's Langley Research Center . LDEF

2400-509: A perigee as low as 80 to 90 km (50 to 56 mi), surviving for multiple orbits. At an altitude of 120 km (75 mi), descending spacecraft such as NASA 's Space Shuttle begin atmospheric entry (termed the Entry Interface), when atmospheric drag becomes noticeable, thus beginning the process of switching from steering with thrusters to maneuvering with aerodynamic control surfaces. The Kármán line , established by

2550-643: A practical boundary have been proposed, ranging from 30 km (19 mi) out to 1,600,000 km (990,000 mi). High-altitude aircraft , such as high-altitude balloons have reached altitudes above Earth of up to 50 km. Up until 2021, the United States designated people who travel above an altitude of 50 mi (80 km) as astronauts. Astronaut wings are now only awarded to spacecraft crew members that "demonstrated activities during flight that were essential to public safety, or contributed to human space flight safety." In 2009, measurements of

2700-612: A processing and control module, a magnetic tape recorder and two LiSO 2 batteries. One experiment (S0069) used a 4-track magnetic tape module not as part of an EPDS. Fifty-seven science and technology experiments — involving government and university investigators from the United States , Canada , Denmark , France , Germany , Ireland , the Netherlands , Switzerland , and the United Kingdom  — flew on

2850-410: A range in mass, as large as 4.5 × 10   M ☉ and as small as 8 × 10   M ☉ . By comparison, the total mass of all the stars in the Milky Way is estimated to be between 4.6 × 10   M ☉ and 6.43 × 10   M ☉ . In addition to the stars, there is also interstellar gas, comprising 90% hydrogen and 10% helium by mass, with two thirds of

3000-426: A simulated Martian environment. The lithopanspermia hypothesis suggests that rocks ejected into outer space from life-harboring planets may successfully transport life forms to another habitable world. A conjecture is that just such a scenario occurred early in the history of the Solar System, with potentially microorganism -bearing rocks being exchanged between Venus, Earth, and Mars. The lack of pressure in space

3150-648: A spacecraft; similarly, " space-based " means based in outer space or on a planet or moon. The size of the whole universe is unknown, and it might be infinite in extent. According to the Big Bang theory, the very early universe was an extremely hot and dense state about 13.8 billion years ago which rapidly expanded . About 380,000 years later the universe had cooled sufficiently to allow protons and electrons to combine and form hydrogen—the so-called recombination epoch . When this happened, matter and energy became decoupled, allowing photons to travel freely through

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3300-415: A treatise in 1755, Immanuel Kant , drawing on earlier work by Thomas Wright , speculated (correctly) that the Milky Way might be a rotating body of a huge number of stars, held together by gravitational forces akin to the Solar System but on much larger scales. The resulting disk of stars would be seen as a band on the sky from our perspective inside the disk. Wright and Kant also conjectured that some of

3450-472: Is a continuous stream of charged particles emanating from the Sun which creates a very tenuous atmosphere (the heliosphere ) for billions of kilometers into space. This wind has a particle density of 5–10 protons /cm and is moving at a velocity of 350–400 km/s (780,000–890,000 mph). Interplanetary space extends out to the heliopause where the influence of the galactic environment starts to dominate over

3600-428: Is a disk of gas and dust called the interstellar medium . This disk has at least a comparable extent in radius to the stars, whereas the thickness of the gas layer ranges from hundreds of light-years for the colder gas to thousands of light-years for warmer gas. The disk of stars in the Milky Way does not have a sharp edge beyond which there are no stars. Rather, the concentration of stars decreases with distance from

3750-405: Is a ring-like filament of stars called Triangulum–Andromeda Ring (TriAnd Ring) rippling above and below the relatively flat galactic plane , which alongside Monoceros Ring were both suggested to be primarily the result of disk oscillations and wrapping around the Milky Way, at a diameter of at least 50 kpc (160,000 ly), which may be part of the Milky Way's outer disk itself, hence making

3900-496: Is about 11,200 m/s (40,300 km/h; 25,100 mph). Orbiting spacecraft with a perigee below about 2,000 km (1,200 mi) are subject to drag from the Earth's atmosphere, which decreases the orbital altitude. The rate of orbital decay depends on the satellite's cross-sectional area and mass, as well as variations in the air density of the upper atmosphere. At altitudes above 800 km (500 mi), orbital lifetime

4050-511: Is about five times the Moon's orbital distance , but which distance is also far less than the distance between Earth and any adjacent planet. Interplanetary space within the Solar System is the space between the eight planets, the space between the planets and the Sun, as well as that space beyond the orbit of the outermost planet Neptune where the solar wind remains active. The solar wind

4200-601: Is also the root of "galaxy", the name for our, and later all such, collections of stars. The Milky Way, or "milk circle", was just one of 11 "circles" the Greeks identified in the sky, others being the zodiac , the meridian , the horizon , the equator , the tropics of Cancer and Capricorn , the Arctic Circle and the Antarctic Circle , and two colure circles passing through both poles. The Milky Way

4350-548: Is approximately 890 billion to 1.54 trillion times the mass of the Sun in total (8.9 × 10 to 1.54 × 10 solar masses), although stars and planets make up only a small part of this. Estimates of the mass of the Milky Way vary, depending upon the method and data used. The low end of the estimate range is 5.8 × 10   solar masses ( M ☉ ), somewhat less than that of the Andromeda Galaxy . Measurements using

4500-453: Is called the Zone of Avoidance . The Milky Way has a relatively low surface brightness . Its visibility can be greatly reduced by background light, such as light pollution or moonlight. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be visible. It should be visible if the limiting magnitude is approximately +5.1 or better and shows

4650-478: Is celestial. This idea would be influential later in the Muslim world . The Persian astronomer Al-Biruni (973–1048) proposed that the Milky Way is "a collection of countless fragments of the nature of nebulous stars". The Andalusian astronomer Avempace ( d 1138) proposed that the Milky Way was made up of many stars but appeared to be a continuous image in the Earth's atmosphere, citing his observation of

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4800-410: Is co-populated by groups of co-orbital Near-Earth Objects (NEOs), such as horseshoe librators and Earth trojans , with some NEOs at times becoming temporary satellites and quasi-moons to Earth. Deep space is defined by the United States government as all of outer space which lies further from Earth than a typical low-Earth-orbit, thus assigning the Moon to deep-space. Other definitions vary

4950-537: Is conventionally used as the start of outer space in space treaties and for aerospace records keeping. Certain portions of the upper stratosphere and the mesosphere are sometimes referred to as "near space". The framework for international space law was established by the Outer Space Treaty , which entered into force on 10 October 1967. This treaty precludes any claims of national sovereignty and permits all states to freely explore outer space . Despite

5100-496: Is divided into overlapping regions of space. Near-Earth space is the region of space extending from low Earth orbits out to geostationary orbits . This region includes the major orbits for artificial satellites and is the site of most of humanity's space activity. The region has seen high levels of space debris, sometimes dubbed space pollution , threatening any space activity in this region. Some of this debris re-enters Earth's atmosphere periodically. Although it meets

5250-438: Is free for all nation states to explore and is not subject to claims of national sovereignty, calling outer space the "province of all mankind". This status as a common heritage of mankind has been used, though not without opposition, to enforce the right to access and shared use of outer space for all nations equally, particularly non-spacefaring nations. It prohibits the deployment of nuclear weapons in outer space. The treaty

5400-472: Is inclined by about 60° to the ecliptic (the plane of Earth's orbit ). Relative to the celestial equator , it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux , indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane. The north galactic pole is situated at right ascension 12 49 , declination +27.4° ( B1950 ) near β Comae Berenices , and

5550-582: Is located at a radius of about 27,000 light-years (8.3 kpc) from the Galactic Center , on the inner edge of the Orion Arm , one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The Galactic Center is an intense radio source known as Sagittarius A* , a supermassive black hole of 4.100 (± 0.034) million solar masses . The oldest stars in

5700-492: Is located beyond the orbit of the Moon and therefore includes cislunar space. Translunar space is the region of lunar transfer orbits , between the Moon and Earth. Cislunar space is a region outside of Earth that includes lunar orbits , the Moon's orbital space around Earth and the Lagrange points . The region where a body's gravitational potential remains dominant against gravitational potentials from other bodies,

5850-475: Is measured in centuries. Below about 300 km (190 mi), decay becomes more rapid with lifetimes measured in days. Once a satellite descends to 180 km (110 mi), it has only hours before it vaporizes in the atmosphere. Space in proximity to the Earth is physically similar to the remainder of interplanetary space, but is home to a multitude of Earth–orbiting satellites and has been subject to extensive studies. For identification purposes, this volume

6000-422: Is measured in terms of the kinetic activity of the gas, as it is on Earth. The radiation of outer space has a different temperature than the kinetic temperature of the gas, meaning that the gas and radiation are not in thermodynamic equilibrium . 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

6150-449: Is not devoid of matter , as it contains a few hydrogen atoms per cubic meter. By comparison, the air humans breathe contains about 10 molecules per cubic meter. The low density of matter in outer space means that electromagnetic radiation can travel great distances without being scattered: the mean free path of a photon in intergalactic space is about 10  km, or 10 billion light years. In spite of this, extinction , which

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6300-485: Is now thought to be purely an invention of Babylonian propagandists with the intention to show Marduk as superior to the Sumerian deities. In Greek mythology , Zeus places his son born by a mortal woman, the infant Heracles , on Hera 's breast while she is asleep so the baby will drink her divine milk and become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes

6450-559: Is quite likely a correspondingly large number of neutrinos called the cosmic neutrino background . ) The current black body temperature of the background radiation is about 2.7 K (−455 °F). The gas temperatures in outer space can vary widely. For example, the temperature in the Boomerang Nebula is 1 K (−458 °F), while the solar corona reaches temperatures over 1,200,000–2,600,000 K (2,200,000–4,700,000 °F). Magnetic fields have been detected in

6600-434: Is significantly smaller than the Andromeda Galaxy's isophotal diameter, and slightly below the mean isophotal sizes of the galaxies being at 28.3 kpc (92,000 ly). The paper concludes that the Milky Way and Andromeda Galaxy were not overly large spiral galaxies, nor were among the largest known (if the former not being the largest) as previously widely believed, but rather average ordinary spiral galaxies. To compare

6750-631: Is slowed by the pressure containment of blood vessels, so some blood remains liquid. Swelling and ebullism can be reduced by containment in a pressure suit . The Crew Altitude Protection Suit (CAPS), a fitted elastic garment designed in the 1960s for astronauts, prevents ebullism at pressures as low as 2 kilopascals (0.3 psi). Supplemental oxygen is needed at 8 km (5 mi) to provide enough oxygen for breathing and to prevent water loss, while above 20 km (12 mi) pressure suits are essential to prevent ebullism. Most space suits use around 30–39 kilopascals (4–6 psi) of pure oxygen, about

6900-664: Is the Large Sagittarius Star Cloud , a portion of the central bulge of the galaxy. Dark regions within the band, such as the Great Rift and the Coalsack , are areas where interstellar dust blocks light from distant stars. Peoples of the southern hemisphere, including the Inca and Australian aborigines , identified these regions as dark cloud constellations . The area of sky that the Milky Way obscures

7050-538: Is the absorption and scattering of photons by dust and gas, is an important factor in galactic and intergalactic astronomy . Stars, planets, and moons retain their atmospheres by gravitational attraction. Atmospheres have no clearly delineated upper boundary: the density of atmospheric gas gradually decreases with distance from the object until it becomes indistinguishable from outer space. The Earth's atmospheric pressure drops to about 0.032 Pa at 100 kilometres (62 miles) of altitude, compared to 100,000 Pa for

7200-451: Is the body's sphere of influence or gravity well, mostly described with the Hill sphere model. In the case of Earth this includes all space from the Earth to a distance of roughly 1% of the mean distance from Earth to the Sun, or 1.5 million km (0.93 million mi). Beyond Earth's Hill sphere extends along Earth's orbital path its orbital and co-orbital space. This space

7350-514: Is the most immediate dangerous characteristic of space to humans. Pressure decreases above Earth, reaching a level at an altitude of around 19.14 km (11.89 mi) that matches the vapor pressure of water at the temperature of the human body . This pressure level is called the Armstrong line , named after American physician Harry G. Armstrong . At or above the Armstrong line, fluids in

7500-752: Is the traditional Welsh name for the Milky Way, and Caer Arianrhod ("The Fortress of Arianrhod ") being the constellation of Corona Borealis . In Western culture, the name "Milky Way" is derived from its appearance as a dim un-resolved "milky" glowing band arching across the night sky. The term is a translation of the Classical Latin via lactea , in turn derived from the Hellenistic Greek γαλαξίας , short for γαλαξίας κύκλος ( galaxías kýklos ), meaning "milky circle". The Ancient Greek γαλαξίας ( galaxias ) – from root γαλακτ -, γάλα ("milk") + -ίας (forming adjectives) –

7650-486: Is visible as a hazy band of white light, some 30° wide, arching the night sky . Although all the individual naked-eye stars in the entire sky are part of the Milky Way Galaxy, the term "Milky Way" is limited to this band of light. The light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane . Brighter regions around the band appear as soft visual patches known as star clouds . The most conspicuous of these

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7800-502: The Andromeda Galaxy was first measured. Humans began the physical exploration of space later in the same century with the advent of high-altitude balloon flights . This was followed by crewed rocket flights and, then, crewed Earth orbit, first achieved by Yuri Gagarin of the Soviet Union in 1961. The economic cost of putting objects, including humans, into space is very high, limiting human spaceflight to low Earth orbit and

7950-475: The Bogotá Declaration , they claimed control of the segment of the geosynchronous orbital path corresponding to each country. These claims are not internationally accepted. An increasing issue of international space law and regulation has been the dangers of the growing number of space debris . A spacecraft enters orbit when its centripetal acceleration due to gravity is less than or equal to

8100-571: The Fédération Aéronautique Internationale , and used internationally by the United Nations , is set at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics. This line is named after Theodore von Kármán , who argued for an altitude where a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from

8250-515: The International Union of Pure and Applied Chemistry (IUPAC) definition of standard pressure . Above this altitude, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar wind . The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather . The temperature of outer space

8400-590: The Kennedy Space Center on January 26. Special efforts were taken to ensure protection against contamination of the payload bay during the ferry flight. Between January 30 and 31, LDEF was removed from Columbia 's payload bay in KSC's Orbiter Processing Facility , placed in a special payload canister, and transported to the Operations and Checkout Building. On February 1, 1990, LDEF was transported in

8550-443: The Moon . On the other hand, uncrewed spacecraft have reached all of the known planets in the Solar System . Outer space represents a challenging environment for human exploration because of the hazards of vacuum and radiation . Microgravity has a negative effect on human physiology that causes both muscle atrophy and bone loss . The use of the short version space , as meaning 'the region beyond Earth's sky', predates

8700-499: The Very Long Baseline Array in 2009 found velocities as large as 254 km/s (570,000 mph) for stars at the outer edge of the Milky Way. Because the orbital velocity depends on the total mass inside the orbital radius, this suggests that the Milky Way is more massive, roughly equaling the mass of Andromeda Galaxy at 7 × 10   M ☉ within 160,000 ly (49 kpc) of its center. In 2010,

8850-513: The background radiation from the Big Bang , is 2.7 kelvins (−270 °C; −455 °F). The plasma between galaxies is thought to account for about half of the baryonic (ordinary) matter in the universe, having a number density of less than one hydrogen atom per cubic metre and a kinetic temperature of millions of kelvins . Local concentrations of matter have condensed into stars and galaxies . Intergalactic space takes up most of

9000-480: The centrifugal acceleration due to the horizontal component of its velocity. For a low Earth orbit , this velocity is about 7,800 m/s (28,100 km/h; 17,400 mph); by contrast, the fastest piloted airplane speed ever achieved (excluding speeds achieved by deorbiting spacecraft) was 2,200 m/s (7,900 km/h; 4,900 mph) in 1967 by the North American X-15 . To achieve an orbit,

9150-514: The cosmic microwave background using satellites like the Wilkinson Microwave Anisotropy Probe . These observations indicate that the spatial geometry of the observable universe is " flat ", meaning that photons on parallel paths at one point remain parallel as they travel through space to the limit of the observable universe, except for local gravity. The flat universe, combined with the measured mass density of

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9300-467: The immune system . Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, and puffiness of the face. During long-duration space travel, radiation can pose an acute health hazard . Exposure to high-energy, ionizing cosmic rays can result in fatigue, nausea, vomiting, as well as damage to the immune system and changes to the white blood cell count. Over longer durations, symptoms include an increased risk of cancer, plus damage to

9450-484: The light-gathering power of this new telescope, he was able to produce astronomical photographs that resolved the outer parts of some spiral nebulae as collections of individual stars. He was also able to identify some Cepheid variables that he could use as a benchmark to estimate the distance to the nebulae. He found that the Andromeda Nebula is 275,000 parsecs from the Sun, far too distant to be part of

9600-614: The magnetic fields of the Milky Way were reported. The Sun is near the inner rim of the Orion Arm , within the Local Fluff of the Local Bubble , between the Radcliffe wave and Split linear structures (formerly Gould Belt ). Based upon studies of stellar orbits around Sgr A* by Gillessen et al. (2016), the Sun lies at an estimated distance of 27.14 ± 0.46 kly (8.32 ± 0.14 kpc) from

9750-440: The nebulae visible in the night sky might be separate "galaxies" themselves, similar to our own. Kant referred to both the Milky Way and the "extragalactic nebulae" as "island universes", a term still current up to the 1930s. The first attempt to describe the shape of the Milky Way and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of

9900-467: The solar apex , is the direction that the Sun travels through space in the Milky Way. The general direction of the Sun's Galactic motion is towards the star Vega near the constellation of Hercules , at an angle of roughly 60 sky degrees to the direction of the Galactic Center. The Sun's orbit about the Milky Way is expected to be roughly elliptical with the addition of perturbations due to

10050-426: The zodiacal light . Interplanetary space contains the magnetic field generated by the Sun. There are magnetospheres generated by planets such as Jupiter, Saturn, Mercury and the Earth that have their own magnetic fields. These are shaped by the influence of the solar wind into the approximation of a teardrop shape, with the long tail extending outward behind the planet. These magnetic fields can trap particles from

10200-421: The Earth's magnetosphere and the solar wind. The inner boundary is the ionosphere . The variable space-weather conditions of geospace are affected by the behavior of the Sun and the solar wind; the subject of geospace is interlinked with heliophysics —the study of the Sun and its impact on the planets of the Solar System. The day-side magnetopause is compressed by solar-wind pressure—the subsolar distance from

10350-571: The Galactic Center is about 180,000 ly (55 kpc). At this distance or beyond, the orbits of most halo objects would be disrupted by the Magellanic Clouds. Hence, such objects would probably be ejected from the vicinity of the Milky Way. The integrated absolute visual magnitude of the Milky Way is estimated to be around −20.9. Both gravitational microlensing and planetary transit observations indicate that there may be at least as many planets bound to stars as there are stars in

10500-530: The Galactic Center. Boehle et al. (2016) found a smaller value of 25.64 ± 0.46 kly (7.86 ± 0.14 kpc), also using a star orbit analysis. The Sun is currently 5–30 parsecs (16–98 ly) above, or north of, the central plane of the Galactic disk. The distance between the local arm and the next arm out, the Perseus Arm , is about 2,000 parsecs (6,500 ly). The Sun, and thus

10650-399: The Galactic spiral arms and non-uniform mass distributions. In addition, the Sun passes through the Galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (damping) term. These oscillations were until recently thought to coincide with mass lifeform extinction periods on Earth. A reanalysis of the effects of

10800-574: The German experiment EXOSTACK, 30% of Bacillus subtilis spores survived the nearly 6 years exposure to outer space when embedded in salt crystals, whereas 80% survived in the presence of glucose , which stabilize the structure of the cellular macromolecules, especially during vacuum-induced dehydration. If shielded against solar UV , spores of B. subtilis were capable of surviving in space for up to 6 years, especially if embedded in clay or meteorite powder (artificial meteorites). The data may support

10950-790: The LDEF Assembly and Transportation System to the Spacecraft Assembly and Encapsulation Facility – 2, where the LDEF project team led deintegration activities. Outer space Outer space (or simply space ) is the expanse that exists beyond Earth's atmosphere and between celestial bodies . It contains ultra-low levels of particle densities , constituting a near-perfect vacuum of predominantly hydrogen and helium plasma , permeated by electromagnetic radiation , cosmic rays , neutrinos , magnetic fields and dust . The baseline temperature of outer space, as set by

11100-600: The LDEF mission. Interstellar gases also would be trapped in an attempt to find clues into the formation of the Milky Way and the evolution of heavier elements. Some examples are investigation of exposure effects on: and physics in low gravity – e.g. crystal growth. At least one of the on-board experiments, the Thermal Control Surfaces Experiment (TCSE), used the RCA 1802 microprocessor. In

11250-708: The Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang . Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe . Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis , observations by Edwin Hubble showed that

11400-405: The Milky Way is "a myriad of tiny stars packed together in the sphere of the fixed stars". Proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars. Galileo also concluded that the appearance of the Milky Way was due to refraction of the Earth's atmosphere. In

11550-446: The Milky Way is approximately 220 km/s (490,000 mph) or 0.073% of the speed of light . The Sun moves through the heliosphere at 84,000 km/h (52,000 mph). At this speed, it takes around 1,400 years for the Solar System to travel a distance of 1 light-year, or 8 days to travel 1 AU ( astronomical unit ). The Solar System is headed in the direction of the zodiacal constellation Scorpius , which follows

11700-525: The Milky Way is just one of many galaxies. In the Babylonian epic poem Enūma Eliš , the Milky Way is created from the severed tail of the primeval salt water dragoness Tiamat , set in the sky by Marduk , the Babylonian national god , after slaying her. This story was once thought to have been based on an older Sumerian version in which Tiamat is instead slain by Enlil of Nippur , but

11850-449: The Milky Way is the glow of stars not directly visible due to Earth's shadow, while other stars receive their light from the Sun, but have their glow obscured by solar rays. Aristotle himself believed that the Milky Way was part of the Earth's upper atmosphere, along with the stars, and that it was a byproduct of stars burning that did not dissipate because of its outermost location in the atmosphere, composing its great circle . He said that

12000-428: The Milky Way seems to be dark matter , an unknown and invisible form of matter that interacts gravitationally with ordinary matter. A dark matter halo is conjectured to spread out relatively uniformly to a distance beyond one hundred kiloparsecs (kpc) from the Galactic Center. Mathematical models of the Milky Way suggest that the mass of dark matter is 1–1.5 × 10   M ☉ . 2013 and 2014 studies indicate

12150-404: The Milky Way". Viewing from the north galactic pole with 0° (zero degrees) as the ray that runs starting from the Sun and through the Galactic Center, the quadrants are: with the galactic longitude (ℓ) increasing in the counter-clockwise direction ( positive rotation ) as viewed from north of the Galactic Center (a view-point several hundred thousand light-years distant from Earth in

12300-514: The Milky Way's galactic plane occupies an area of the sky that includes 30 constellations . The Galactic Center lies in the direction of Sagittarius , where the Milky Way is brightest. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga . The band then continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two roughly equal hemispheres . The galactic plane

12450-530: The Milky Way, and microlensing measurements indicate that there are more rogue planets not bound to host stars than there are stars. The Milky Way contains an average of at least one planet per star, resulting in 100–400 billion planets, according to a January 2013 study of the five-planet star system Kepler-32 by the Kepler space observatory. A different January 2013 analysis of Kepler data estimated that at least 17 billion Earth-sized exoplanets reside in

12600-438: The Milky Way. The ESA spacecraft Gaia provides distance estimates by determining the parallax of a billion stars and is mapping the Milky Way with four planned releases of maps in 2016, 2018, 2021 and 2024. Data from Gaia has been described as "transformational". It has been estimated that Gaia has expanded the number of observations of stars from about 2 million stars as of the 1990s to 2 billion. It has expanded

12750-437: The Milky Way. In November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest exoplanet may be 4.2 light-years away, orbiting the red dwarf Proxima Centauri , according to

12900-501: The Solar System, is located in the Milky Way's galactic habitable zone . There are about 208 stars brighter than absolute magnitude  8.5 within a sphere with a radius of 15 parsecs (49 ly) from the Sun, giving a density of one star per 69 cubic parsecs, or one star per 2,360 cubic light-years (from List of nearest bright stars ). On the other hand, there are 64 known stars (of any magnitude, not counting 4  brown dwarfs ) within 5 parsecs (16 ly) of

13050-411: The Sun's transit through the spiral structure based on CO data has failed to find a correlation. It takes the Solar System about 240 million years to complete one orbit of the Milky Way (a galactic year ), so the Sun is thought to have completed 18–20 orbits during its lifetime and 1/1250 of a revolution since the origin of humans . The orbital speed of the Solar System about the center of

13200-412: The Sun, giving a density of about one star per 8.2 cubic parsecs, or one per 284 cubic light-years (from List of nearest stars ). This illustrates the fact that there are far more faint stars than bright stars: in the entire sky, there are about 500 stars brighter than apparent magnitude  4 but 15.5 million stars brighter than apparent magnitude 14. The apex of the Sun's way, or

13350-452: The Sun. It is the space between the stars or stellar systems within a nebula or galaxy. Interstellar space contains an interstellar medium of sparse matter and radiation. The boundary between an astrosphere and interstellar space is known as an astropause . For the Sun, the astrosphere and astropause are called the heliosphere and heliopause. Approximately 70% of the mass of the interstellar medium consists of lone hydrogen atoms; most of

13500-736: The atmosphere to support itself, which he calculated to be at an altitude of about 83.8 km (52.1 mi). This distinguishes altitudes below as the region of aerodynamics and airspace , and above as the space of astronautics and free space . There is no internationally recognized legal altitude limit on national airspace, although the Kármán line is the most frequently used for this purpose. Objections have been made to setting this limit too high, as it could inhibit space activities due to concerns about airspace violations. It has been argued for setting no specified singular altitude in international law, instead applying different limits depending on

13650-487: The baby away, some of her milk spills, and it produces the band of light known as the Milky Way. In another Greek story, the abandoned Heracles is given by Athena to Hera for feeding, but Heracles' forcefulness causes Hera to rip him from her breast in pain. Llys Dôn (literally "The Court of Dôn ") is the traditional Welsh name for the constellation Cassiopeia . At least three of Dôn's children also have astronomical associations: Caer Gwydion ("The fortress of Gwydion ")

13800-498: The blood empties into the lungs to try to equalize the partial pressure gradient. Once the deoxygenated blood arrives at the brain, humans lose consciousness after a few seconds and die of hypoxia within minutes. Blood and other body fluids boil when the pressure drops below 6.3 kilopascals (1 psi), and this condition is called ebullism . The steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Ebullism

13950-399: The body adjusts to the new environment. Longer-term exposure to weightlessness results in muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia . These effects can be minimized through a regimen of exercise. Other effects include fluid redistribution, slowing of the cardiovascular system , decreased production of red blood cells , balance disorders, and a weakening of

14100-507: The case, in particular based on the craft and its purpose. Spacecraft have flown over foreign countries as low as 30 km (19 mi), as in the example of the Space Shuttle. The Outer Space Treaty provides the basic framework for international space law. It covers the legal use of outer space by nation states, and includes in its definition of outer space , the Moon, and other celestial bodies. The treaty states that outer space

14250-414: The center of the Earth is typically 10 Earth radii. On the night side, the solar wind stretches the magnetosphere to form a magnetotail that sometimes extends out to more than 100–200 Earth radii. For roughly four days of each month, the lunar surface is shielded from the solar wind as the Moon passes through the magnetotail. Geospace is populated by electrically charged particles at very low densities,

14400-482: The center of the Milky Way. Beyond a radius of roughly 40,000 light years (13 kpc) from the center, the number of stars per cubic parsec drops much faster with radius. Surrounding the galactic disk is a spherical galactic halo of stars and globular clusters that extends farther outward, but is limited in size by the orbits of two Milky Way satellites, the Large and Small Magellanic Clouds , whose closest approach to

14550-447: The continually expanding space. Matter that remained following the initial expansion has since undergone gravitational collapse to create stars, galaxies and other astronomical objects, leaving behind a deep vacuum that forms what is now called outer space. As light has a finite velocity, this theory constrains the size of the directly observable universe. The present day shape of the universe has been determined from measurements of

14700-406: The cosmic rays upon the shielding produces additional radiation that can affect the crew. Further research is needed to assess the radiation hazards and determine suitable countermeasures. The transition between Earth's atmosphere and outer space lacks a well-defined physical boundary, with the air pressure steadily decreasing with altitude until it mixes with the solar wind. Various definitions for

14850-450: The definition of outer space, the atmospheric density inside low-Earth orbital space, the first few hundred kilometers above the Kármán line, is still sufficient to produce significant drag on satellites. Geospace is a region of space that includes Earth's upper atmosphere and magnetosphere . The Van Allen radiation belts lie within the geospace. The outer boundary of geospace is the magnetopause , which forms an interface between

15000-477: The deploying astronauts next to the active grapple fixture. Engineers originally intended that the first mission would last about one year, and that several long-duration exposure missions would use the same frame. The exposure facility was actually used for a single 5.7-year mission. The LDEF facility was designed to glean information vital to the development of the Space Station Freedom (that

15150-422: The direction and speed of ions in the atmosphere were made from a sounding rocket . The altitude of 118 km (73.3 mi) above Earth was the midpoint for charged particles transitioning from the gentle winds of the Earth's atmosphere to the more extreme flows of outer space. The latter can reach velocities well over 268 m/s (880 ft/s). Spacecraft have entered into a highly elliptical orbit with

15300-412: The direction of the constellation Coma Berenices ); if viewed from south of the Galactic Center (a view-point similarly distant in the constellation Sculptor ), ℓ would increase in the clockwise direction ( negative rotation ). The Milky Way is one of the two largest galaxies in the Local Group (the other being the Andromeda Galaxy ), although the size for its galactic disc and how much it defines

15450-456: The drafting of UN resolutions for the peaceful uses of outer space, anti-satellite weapons have been tested in Earth orbit . The concept that the space between the Earth and the Moon must be a vacuum was first proposed in the 17th century after scientists discovered that air pressure decreased with altitude. The immense scale of outer space was grasped in the 20th century when the distance to

15600-469: The ecliptic. A galactic quadrant, or quadrant of the Milky Way, refers to one of four circular sectors in the division of the Milky Way. In astronomical practice, the delineation of the galactic quadrants is based upon the galactic coordinate system , which places the Sun as the origin of the mapping system . Quadrants are described using ordinals  – for example, "1st galactic quadrant", "second galactic quadrant", or "third quadrant of

15750-436: The eyes, nervous system , lungs and the gastrointestinal tract . On a round-trip Mars mission lasting three years, a large fraction of the cells in an astronaut's body would be traversed and potentially damaged by high energy nuclei. The energy of such particles is significantly diminished by the shielding provided by the walls of a spacecraft and can be further diminished by water containers and other barriers. The impact of

15900-485: The harsh environment, several life forms have been found that can withstand extreme space conditions for extended periods. Species of lichen carried on the ESA BIOPAN facility survived exposure for ten days in 2007. Seeds of Arabidopsis thaliana and Nicotiana tabacum germinated after being exposed to space for 1.5 years. A strain of Bacillus subtilis has survived 559 days when exposed to low Earth orbit or

16050-599: The high energy range, the flux of electrons is only about 1% of that of protons. Cosmic rays can damage electronic components and pose a health threat to space travelers. Smells produced returning from low Earth orbit extravehicular activity have a burned/metallic odor, similar to the scent of arc welding fumes, resulting from oxygen in low Earth orbit around the ISS, which clings to suits and equipment. Other regions of space could have very different smells, like that of different alcohols in molecular clouds . Despite

16200-409: The hydrogen found in the atomic form and the remaining one-third as molecular hydrogen . The mass of the Milky Way's interstellar gas is equal to between 10% and 15% of the total mass of its stars. Interstellar dust accounts for an additional 1% of the total mass of the gas. In March 2019, astronomers reported that the virial mass of the Milky Way Galaxy is 1.54 trillion solar masses within

16350-623: The international co-operation in the peaceful uses of outer space and preventing an arms race in space. Four additional space law treaties have been negotiated and drafted by the UN's Committee on the Peaceful Uses of Outer Space . Still, there remains no legal prohibition against deploying conventional weapons in space, and anti-satellite weapons have been successfully tested by the USA, USSR, China, and in 2019, India. The 1979 Moon Treaty turned

16500-422: The interstellar medium, including the heavy elements previously formed within the star's core. The density of matter in the interstellar medium can vary considerably: the average is around 10 particles per m , but cold molecular clouds can hold 10 –10 per m . Milky Way The Milky Way is the galaxy that includes the Solar System , with the name describing the galaxy's appearance from Earth :

16650-436: The isophotal diameter is not well understood. It is estimated that the significant bulk of stars in the galaxy lies within the 26 kiloparsecs (80,000 light-years) diameter, and that the number of stars beyond the outermost disc dramatically reduces to a very low number, with respect to an extrapolation of the exponential disk with the scale length of the inner disc. There are several methods being used in astronomy in defining

16800-603: The jurisdiction of all heavenly bodies (including the orbits around such bodies) over to the international community. The treaty has not been ratified by any nation that currently practices human spaceflight. In 1976, eight equatorial states (Ecuador, Colombia, Brazil, The Republic of the Congo, Zaire, Uganda, Kenya, and Indonesia) met in Bogotá, Colombia: with their "Declaration of the First Meeting of Equatorial Countries", or

16950-442: The large pressure differential between inside and outside the chest. Even if the subject's airway is fully open, the flow of air through the windpipe may be too slow to prevent the rupture. Rapid decompression can rupture eardrums and sinuses, bruising and blood seep can occur in soft tissues, and shock can cause an increase in oxygen consumption that leads to hypoxia . As a consequence of rapid decompression, oxygen dissolved in

17100-478: The likelihood of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis. The Space Exposed Experiment Developed for Students (SEEDS) allowed students the opportunity to grow control and experimental tomato seeds that had been exposed on LDEF comparing and reporting the results. 12.5 million seeds were flown, and students from elementary to graduate school returned 8000 reports to NASA. The L.A. Times misreported that

17250-404: The magnetic field and particle flux from the Sun. The distance and strength of the heliopause varies depending on the activity level of the solar wind. The heliopause in turn deflects away low-energy galactic cosmic rays, with this modulation effect peaking during solar maximum. The volume of interplanetary space is a nearly total vacuum, with a mean free path of about one astronomical unit at

17400-526: The measurable volume of space by a factor of 100 in radius and a factor of 1,000 in precision. A study in 2020 concluded that Gaia detected a wobbling motion of the galaxy, which might be caused by " torques from a misalignment of the disc's rotation axis with respect to the principal axis of a non-spherical halo, or from accreted matter in the halo acquired during late infall, or from nearby, interacting satellite galaxies and their consequent tides". In April 2024, initial studies (and related maps) involving

17550-531: The milky appearance of the Milky Way Galaxy is due to the refraction of the Earth's atmosphere. The Neoplatonist philosopher Olympiodorus the Younger ( c.  495 –570 AD) criticized this view, arguing that if the Milky Way were sublunary , it should appear different at different times and places on Earth, and that it should have parallax , which it does not. In his view, the Milky Way

17700-518: The most distant high-z sources, indicating the presence of magnetic fields. Outside a protective atmosphere and magnetic field, there are few obstacles to the passage through space of energetic subatomic particles known as cosmic rays. These particles have energies ranging from about 10   eV up to an extreme 10  eV of ultra-high-energy cosmic rays . The peak flux of cosmic rays occurs at energies of about 10  eV, with approximately 87% protons, 12% helium nuclei and 1% heavier nuclei. In

17850-525: The motions of which are controlled by the Earth's magnetic field . These plasmas form a medium from which storm-like disturbances powered by the solar wind can drive electrical currents into the Earth's upper atmosphere. Geomagnetic storms can disturb two regions of geospace, the radiation belts and the ionosphere. These storms increase fluxes of energetic electrons that can permanently damage satellite electronics, interfering with shortwave radio communication and GPS location and timing. Magnetic storms can be

18000-589: The nature of the Milky Way, spiral nebulae, and the dimensions of the Universe. To support his claim that the Great Andromeda Nebula is an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in the Milky Way, as well as the significant Doppler shift . The controversy was conclusively settled by Edwin Hubble in the early 1920s using the Mount Wilson observatory 2.5 m (100 in) Hooker telescope . With

18150-405: The number of very-low-mass stars, which are difficult to detect, especially at distances of more than 300 ly (90 pc) from the Sun. As a comparison, the neighboring Andromeda Galaxy contains an estimated one trillion (10 ) stars. The Milky Way may contain ten billion white dwarfs , a billion neutron stars , and a hundred million stellar black holes . Filling the space between the stars

18300-433: The old population of the galactic halo. A 2020 study predicted the edge of the Milky Way's dark matter halo being around 292 ± 61  kpc (952,000 ± 199,000  ly ), which translates to a diameter of 584 ± 122  kpc (1.905 ± 0.3979  Mly ). The Milky Way's stellar disk is also estimated to be approximately up to 1.35 kpc (4,000 ly) thick. The Milky Way

18450-499: The ones in the Milky Way, and modelling the relationship to their surface brightnesses. This gave an isophotal diameter for the Milky Way at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years), by assuming that the galactic disc is well represented by an exponential disc and adopting a central surface brightness of the galaxy (μ 0 ) of 22.1 ± 0.3 B -mag/arcsec and a disk scale length ( h ) of 5.0 ± 0.5 kpc (16,300 ± 1,600 ly). This

18600-403: The orbital distance of the Earth. This space is not completely empty, and is sparsely filled with cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is gas, plasma and dust, small meteors , and several dozen types of organic molecules discovered to date by microwave spectroscopy . A cloud of interplanetary dust is visible at night as a faint band called

18750-528: The photographic record, he found 11 more novae . Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within the Milky Way. As a result, he was able to come up with a distance estimate of 150,000 parsecs. He became a proponent of the "island universes" hypothesis, which held that the spiral nebulae were independent galaxies. In 1920 the Great Debate took place between Harlow Shapley and Heber Curtis, concerning

18900-400: The relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter (24.3 mm (0.955 in)), the Milky Way would be approximately at least the greatest north–south line of the contiguous United States . An even older study from 1978 gave a lower diameter for Milky Way about 23 kpc (75,000 ly). A 2015 paper discovered that there

19050-439: The remainder consists of helium atoms. This is enriched with trace amounts of heavier atoms formed through stellar nucleosynthesis . These atoms are ejected into the interstellar medium by stellar winds or when evolved stars begin to shed their outer envelopes such as during the formation of a planetary nebula . The cataclysmic explosion of a supernova propagates shock waves of stellar ejecta outward, distributing it throughout

19200-503: The retrieval mission first to 1986, then indefinitely due to the Challenger disaster . After 5.7 years its orbit had decayed to about 175 nautical miles (324 km) and it was likely to burn up on reentry in a little over a month. It was finally recovered by Columbia on mission STS-32 on January 12, 1990. Columbia approached LDEF in such a way as to minimize possible contamination to LDEF from thruster exhaust. While LDEF

19350-640: The same as the partial pressure of oxygen at the Earth's surface. This pressure is high enough to prevent ebullism, but evaporation of nitrogen dissolved in the blood could still cause decompression sickness and gas embolisms if not managed. Humans evolved for life in Earth gravity , and exposure to weightlessness has been shown to have deleterious effects on human health. Initially, more than 50% of astronauts experience space motion sickness . This can cause nausea and vomiting, vertigo , headaches, lethargy , and overall malaise. The duration of space sickness varies, but it typically lasts for 1–3 days, after which

19500-516: The size of a galaxy, and each of them can yield different results with respect to one another. The most commonly employed method is the D 25 standard – the isophote where the photometric brightness of a galaxy in the B-band (445 nm wavelength of light, in the blue part of the visible spectrum ) reaches 25 mag/arcsec . An estimate from 1997 by Goodwin and others compared the distribution of Cepheid variable stars in 17 other spiral galaxies to

19650-473: The solar wind and other sources, creating belts of charged particles such as the Van Allen radiation belts. Planets without magnetic fields, such as Mars, have their atmospheres gradually eroded by the solar wind. Interstellar space is the physical space outside of the bubbles of plasma known as astrospheres , formed by stellar winds originating from individual stars, or formed by solar wind emanating from

19800-542: The south galactic pole is near α Sculptoris . Because of this high inclination, depending on the time of night and year, the Milky Way arch may appear relatively low or relatively high in the sky. For observers from latitudes approximately 65° north to 65° south, the Milky Way passes directly overhead twice a day. In Meteorologica , Aristotle (384–322 BC) states that the Greek philosophers Anaxagoras ( c.  500 –428 BC) and Democritus (460–370 BC) proposed that

19950-625: The space around just about every class of celestial object. Star formation in spiral galaxies can generate small-scale dynamos , creating turbulent magnetic field strengths of around 5–10 μ G . The Davis–Greenstein effect causes elongated dust grains to align themselves with a galaxy's magnetic field, resulting in weak optical polarization . This has been used to show ordered magnetic fields that exist in several nearby galaxies. Magneto-hydrodynamic processes in active elliptical galaxies produce their characteristic jets and radio lobes . Non-thermal radio sources have been detected even among

20100-409: The starting point of deep-space from, "That which lies beyond the orbit of the moon," to "That which lies beyond the farthest reaches of the Solar System itself." The International Telecommunication Union responsible for radio communication , including with satellites, defines deep-space as, "distances from the Earth equal to, or greater than, 2 million km (1.2 million mi)," which

20250-524: The stellar disk larger by increasing to this size. A more recent 2018 paper later somewhat ruled out this hypothesis, and supported a conclusion that the Monoceros Ring, A13 and TriAnd Ring were stellar overdensities rather kicked out from the main stellar disk, with the velocity dispersion of the RR Lyrae stars found to be higher and consistent with halo membership. Another 2018 study revealed

20400-407: The throat and lungs boil away. More specifically, exposed bodily liquids such as saliva, tears, and liquids in the lungs boil away. Hence, at this altitude, human survival requires a pressure suit, or a pressurized capsule. Out in space, sudden exposure of an unprotected human to very low pressure , such as during a rapid decompression, can cause pulmonary barotrauma —a rupture of the lungs, due to

20550-427: The universe and the accelerating expansion of the universe , indicates that space has a non-zero vacuum energy , which is called dark energy . Estimates put the average energy density of the present day universe at the equivalent of 5.9 protons per cubic meter, including dark energy, dark matter, and baryonic matter (ordinary matter composed of atoms). The atoms account for only 4.6% of the total energy density, or

20700-508: The universe, the Milky Way galaxy has a below average amount of neutrino luminosity making our galaxy a " neutrino desert ". The Milky Way consists of a bar-shaped core region surrounded by a warped disk of gas, dust and stars. The mass distribution within the Milky Way closely resembles the type Sbc in the Hubble classification , which represents spiral galaxies with relatively loosely wound arms. Astronomers first began to conjecture that

20850-483: The use of full term "outer space", with the earliest recorded use of this meaning in an epic poem by John Milton called Paradise Lost , published in 1667. The term outward space existed in a poem from 1842 by the English poet Lady Emmeline Stuart-Wortley called "The Maiden of Moscow", but in astronomy the term outer space found its application for the first time in 1845 by Alexander von Humboldt . The term

21000-399: The very probable presence of disk stars at 26–31.5 kpc (84,800–103,000 ly) from the Galactic Center or perhaps even farther, significantly beyond approximately 13–20 kpc (40,000–70,000 ly), in which it was once believed to be the abrupt drop-off of the stellar density of the disk, meaning that few or no stars were expected to be above this limit, save for stars that belong to

21150-478: The visible sky. He produced a diagram of the shape of the Milky Way with the Solar System close to the center. In 1845, Lord Rosse constructed a new telescope and was able to distinguish between elliptical and spiral-shaped nebulae. He also managed to make out individual point sources in some of these nebulae, lending credence to Kant's earlier conjecture. In 1904, studying the proper motions of stars, Jacobus Kapteyn reported that these were not random, as it

21300-399: The volume of the universe , but even galaxies and star systems consist almost entirely of empty space. Most of the remaining mass-energy in the observable universe is made up of an unknown form, dubbed dark matter and dark energy . Outer space does not begin at a definite altitude above Earth's surface. The Kármán line , an altitude of 100 km (62 mi) above sea level ,

21450-575: Was a 12 sided prism (to fit the shuttle orbiter payload bay), and made entirely from stainless steel . There were 5 or 6 experiments on each of the 12 long sides and a few more on the ends. It was designed to fly with one end facing earth and the other away from earth. Attitude control of LDEF was achieved with gravity-gradient stabilization and inertial distribution to maintain three-axis stability in orbit. Therefore, propulsion or other attitude control systems were not required, making LDEF free of acceleration forces and contaminants from jet firings. There

21600-515: Was also a magnetic/viscous damper to stop any initial oscillation after deployment. It had two grapple fixtures . An FRGF and an active (rigidize sensing) grapple used to send an electronic signal to initiate the 19 experiments that had electrical systems. This activated the Experiment Initiate System (EIS) which sent 24 initiation signals to the 20 active experiments. There were six initiation indications which were visible to

21750-515: Was believed in that time; stars could be divided into two streams, moving in nearly opposite directions. It was later realized that Kapteyn's data had been the first evidence of the rotation of our galaxy, which ultimately led to the finding of galactic rotation by Bertil Lindblad and Jan Oort . In 1917, Heber Doust Curtis had observed the nova S Andromedae within the Great Andromeda Nebula ( Messier object 31). Searching

21900-524: Was eventually built as the International Space Station ) and other spacecraft, especially the reactions of various space building materials to radiation, extreme temperature changes and collisions with space matter. Some of the experiments had a cover that opened after deployment and was designed to close after about a year, e.g. , Space Environment Effects (M0006). There was no telemetry, but some active experiments recorded data on

22050-457: Was eventually popularized through the writings of H. G. Wells after 1901. Theodore von Kármán used the term of free space to name the space of altitudes above Earth where spacecrafts reach conditions sufficiently free from atmospheric drag, differentiating it from airspace , identifying a legal space above territories free from the sovereign jurisdiction of countries. " Spaceborne " denotes existing in outer space, especially if carried by

22200-415: Was intended to be reused, and redeployed with new experiments, perhaps every 18 months. but after the unintended extension of mission 1 the structure itself was treated as an experiment and intensively studied before being placed into storage. The STS-41-C crew of Challenger deployed LDEF on April 7, 1984, into a nearly circular orbit at an altitude of 257 nautical miles. The LDEF structure shape

22350-671: Was passed by the United Nations General Assembly in 1963 and signed in 1967 by the Union of Soviet Socialist Republics (USSR), the United States of America (USA), and the United Kingdom (UK). As of 2017, 105 state parties have either ratified or acceded to the treaty. An additional 25 states signed the treaty, without ratifying it. Since 1958, outer space has been the subject of multiple United Nations resolutions. Of these, more than 50 have been concerning

22500-556: Was still attached to the RMS arm, an extensive 4.5 hour survey photographed each individual experiment tray, as well as larger areas. Nevertheless, shuttle operations did contaminate experiments when concerns for human comfort out-weighed important LDEF mission goals. Columbia landed at Edwards Air Force Base on January 20, 1990. With LDEF still in its bay, Columbia was ferried back on the Shuttle Carrier Aircraft to

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