Introduction
![The lower half shows a blue planet with patchy white clouds. The upper half has a man in a white spacesuit and maneuvering unit against a black background.](https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Bruce_McCandless_II_during_EVA_in_1984.jpg/170px-Bruce_McCandless_II_during_EVA_in_1984.jpg)
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 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 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, 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 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 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 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. (Full article...)
Selected article
A dwarf planet is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighbouring region of planetesimals and is not a satellite. They are smaller than planets, but more massive than small solar system bodies. The term was adopted in 2006 by the International Astronomical Union (IAU) as a result of the increase in discoveries of trans-Neptunian objects that rivaled Pluto in size, and finally precipitated by the discovery of an even more massive object, Eris. The IAU currently recognizes five dwarf planets—Ceres (pictured), Pluto, Haumea, Makemake, and Eris. It is suspected that at least another 40 known objects in the Solar System are dwarf planets, but the number might be as high as 2,000. The 2006 definition has been both praised and criticized, and has been disputed by some scientists.
Selected picture
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Image 1The Pillars of Creation, a series of elephant trunks of interstellar gas and dust in the Eagle Nebula, are the subject of a famous Hubble Space Telescope photograph taken in 1995. They are so named because the depicted gas and dust, while being eroded by the light from nearby stars, are in the process of creating new stars. Shown here is a 2014 rephotograph, which was unveiled in 2015 as part of the telescope's 25th anniversary celebrations.
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Image 2
Kepler's Supernova Credit: NASAThis Supernova remnant of Kepler's Supernova (SN 1604) is made up of the materials left behind by the gigantic explosion of a star. There are two possible routes to this end: either a massive star may cease to generate fusion energy in its core, and collapse inward under the force of its own gravity, or a white dwarf star may accumulate material from a companion star until it reaches a critical mass and undergoes a similar collapse. In either case, the resulting supernova explosion expels much or all of the stellar material with great force. -
Image 3The Sombrero Galaxy is a spiral galaxy in the Virgo constellation. It was discovered in the late 1700s. It is about 28 million light years away and is just faint enough to be invisible to the naked eye but easily visible with small telescopes. In our sky, it is about one-fifth the diameter of the full moon. M104 is moving away from Earth at about 1,000 kilometers per second.
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Image 4Image credit: Dave JarvisAn illustration of relative astronomical orders of magnitude, starting with the terrestrial planets of the Solar System in image 1 (top left) and ending with the largest known star, VY Canis Majoris, at the bottom right. The biggest celestial body in each image is shown on the left of the next frame.
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Image 5Photo: Adam EvansThe Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years away. The image, created using a hydrogen-alpha filter, also shows Messier objects 32 and 110, as well as NGC 206 and the star Nu Andromedae. On December 15, 1612, German astronomer Simon Marius became the first person to describe the galaxy using a telescope.
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Image 6Photograph: NASA/JPL-Caltech/University of ArizonaThe Helix Nebula is a large planetary nebula located in the constellation Aquarius. Discovered by Karl Ludwig Harding, probably before 1824, it is one of the closest to Earth of all the bright planetary nebulae, about 215 parsecs (700 light-years) away. It is similar in appearance to the Cat's Eye Nebula and the Ring Nebula.
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Image 7Animation credit: CmgleeThis is an animation showing geocentric satellite orbits, to scale with the Earth, at 3,600 times actual speed. The second-outermost (shown in grey) is a geostationary orbit, 35,786 kilometres (22,236 miles) above Earth's equator and following the direction of Earth's rotation, with an orbital period matching the planet's rotation period (a geosynchronous orbit). An object in such an orbit will appear to occupy a fixed position in the sky. Some 300 kilometres (190 miles) farther away is the graveyard orbit (brown), used for satellites at the end of their operational lives. Nearer to the Earth are the orbits of navigational satellites, such as Galileo (turquoise), BeiDou (beige), GPS (blue) and GLONASS (red), in medium Earth orbits. Much closer to the planet, and within the inner Van Allen belt, are satellites in low Earth orbit, such as the Iridium satellite constellation (purple), the Hubble Space Telescope (green) and the International Space Station (magenta).
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Image 8Uranus is the seventh planet from the Sun and the fourth most massive in the Solar System. In this photograph from 1986 the planet appears almost featureless, but recent terrestrial observations have found seasonal changes to be occurring.
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Image 9Photo credit: New Horizons probeAn animation of an eruption by the Tvashtar Paterae volcanic region on the innermost of Jupiter's Galilean moons, Io. The ejecta plume is 330 km (205 mi) high, though only its uppermost half is visible in this image, as its source lies over the moon's limb on its far side. This animation consists of a sequence of five images taken by NASA's New Horizons probe on March 1, 2007, over the course of eight minutes from 23:50 UTC.
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Image 10Photo: Yuri Beletsky, ESOA laser shoots towards the centre of the Milky Way from the Very Large Telescope facility in Chile, to provide a laser guide star, a reference point in the sky for the telescope's adaptive optics (AO) system. AO technology improves the performance of optical systems by reducing the effect of atmospheric distortion. AO was first envisioned by Horace W. Babcock in 1953, but did not come into common usage until advances in computer technology during the 1990s made the technique practical.
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Image 11Photo: NASA/Crew of Expedition 22Space Shuttle Endeavour in a photograph taken from the International Space Station, in which the shuttle appears to straddle the stratosphere and mesosphere. During this mission, STS-130, the shuttle's primary payloads were the Tranquility module and the Cupola, a robotic control station which provides a 360-degree view around the station.
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Image 12
Earthrise, as seen by Apollo 8 Credit: William Anders"Earthrise," the first occasion in which humans saw the Earth seemingly rising above the surface of the Moon, taken during the Apollo 8 mission on December 24, 1968. This view was seen by the crew at the beginning of its fourth orbit around the Moon, although the very first photograph taken was in black-and-white. Note that the Earth is in shadow here. A photo of a fully lit Earth would not be taken until the Apollo 17 mission. -
Image 13A TRACE image of sunspots on the surface, or photosphere, of the sun from September 2002, is taken in the far ultraviolet on a relatively quiet day for solar activity. However, the image still shows a large sunspot group visible as a bright area near the horizon. Although sunspots are relatively cool regions on the surface of the sun, the bright glowing gas flowing around the sunspots have a temperature of over one million °C (1.8 million °F). The high temperatures are thought to be related to the rapidly changing magnetic field loops that channel solar plasma.
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Image 14Photograph: NASA, ESA, A. Aloisi (STScI/ESA), and The Hubble Heritage (STScI/AURA)-ESA/Hubble CollaborationAn image of NGC 4449, highlighting its qualities as a starburst galaxy. NGC 4449, an irregular galaxy in the constellation Canes Venatici located about 12 million light years from Earth, has a rate of star formation twice that of the Milky Way's satellite galaxy, the Large Magellanic Cloud. Interactions with nearby galaxies are thought to have influenced this star formation.
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Image 15
Planet Mars Credit: NASAMars, the fourth planet from the Sun, is named after the Roman god of war because of its blood red color. Mars has two small, oddly-shaped moons, Phobos and Deimos, named after the sons of the Greek god Ares. At some point in the future Phobos will be broken up by gravitational forces. The atmosphere on Mars is 95% carbon dioxide. In 2003 methane was also discovered in the atmosphere. Since methane is an unstable gas, this indicates that there must be (or have been within the last few hundred years) a source of the gas on the planet. -
Image 16Photograph credit: NASA / JPL / Space Science InstituteThe Cassini–Huygens space-research project involved a collaboration between NASA, the European Space Agency, and the Italian Space Agency to send a probe to study the planet Saturn and its system, including its rings and its natural satellites.
This natural-color mosaic image, combining thirty photographs, was taken by the Cassini orbiter over the course of approximately two hours on 23 July 2008 as it panned its wide-angle camera across Saturn and its ring system as the planet approached equinox. Six moons are pictured in the panorama, with the largest, Titan, visible at the bottom left. -
Image 17NASA astronaut Robert Curbeam (left) and European Space Agency (ESA) astronaut Christer Fuglesang participate in STS-116's first of three planned sessions of extra-vehicular activity (EVA) as construction resumes on the International Space Station. The landmasses depicted in the background are the South Island (left) and North Island (right) of New Zealand.
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Image 18Map credit: Ignace-Gaston PardiesIgnace-Gaston Pardies (1636–1673) was a French Catholic priest and scientist. His celestial atlas, entitled Globi coelestis in tabulas planas redacti descriptio, comprised six charts of the night sky and was first published in 1674. The atlas uses a gnomonic projection so that the plates make up a cube of the celestial sphere. The constellation figures are drawn from Uranometria, but were carefully reworked and adapted to a broader view of the sky. This is the second plate from a 1693 edition of Pardies's atlas, featuring constellations including Pegasus and Andromeda, visible in the northern sky.
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Image 19A timed exposure of the first Space Shuttle mission, STS-1. The shuttle Columbia stands on launch pad A at Kennedy Space Center, the night before launch. The objectives of the maiden flight were to check out the overall Shuttle system, accomplish a safe ascent into orbit and to return to Earth for a safe landing.
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Image 20Image credit: NASAA radar image of the surface of Venus, centered at 180 degrees east longitude. This composite image was created from mapping by the Magellan probe, supplemented by data gathered by the Pioneer orbiter, with simulated hues based on color images recorded by Venera 13 and 14. No probe has been able to survive more than a few hours on Venus's surface, which is completely obscured by clouds, because the atmospheric pressure is some 90 times that of the Earth's, and its surface temperature is around 450 °C (842 °F).
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Image 21The launch of Space Shuttle Atlantis on STS-98, February 7 2001, at sunset. The sun is behind the camera, and the shape of the plume is cast across the vault of the sky, intersecting the rising full moon. The top portion of the plume is bright because it is illuminated directly by the sun; the lower portions are in the Earth's shadow. After launch, the shuttle must engage in a pitch and roll program so that the vehicle is below the external tank and SRBs, as evidenced in the plume trail. The vehicle climbs in a progressively flattening arc, because achieving low orbit requires much more horizontal than vertical acceleration.
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Image 22A composite photo of the Orion Nebula, the closest region of star formation to Earth. It is composed of 520 separate images and NASA calls it "one of the most detailed astronomical images ever produced". The nebula is located below Orion's Belt and is visible to the naked eye at night. It is one of the most scrutinized and photographed objects in the night sky, and is among the most intensely-studied celestial features.
Space-related portals
General images
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Image 1Space debris identified as WT1190F, burning up in a fireball over Sri Lanka. (from Space debris)
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Image 2Artistic image of a rocket lifting from a Saturn moon (from Space exploration)
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Image 4Voyager 1 is the first artificial object to reach the interstellar medium. (from Interstellar medium)
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Image 5Conventional anti-satellite weapons such as the SM-3 missile remain legal under space law, even though they create hazardous space debris (from Outer space)
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Image 7Apollo 16 LEM Orion, the Lunar Roving Vehicle and astronaut John Young (1972) (from Space exploration)
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Image 8A proposed timeline of the origin of space, from physical cosmology (from Outline of space science)
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Image 9A dusty trail from the early Solar System to carbonaceous dust today. (from Cosmic dust)
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Image 10Without regulation, debris is only expected to grow. (from Space debris)
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Image 11Objects in Earth orbit including fragmentation debris, November 2020, NASA: ODPO (from Space debris)
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Image 12After reentry, Delta 2 second stage pieces were found in South Africa. (from Space debris)
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Image 14Astronaut Buzz Aldrin had a personal Communion service when he first arrived on the surface of the Moon. (from Space exploration)
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Image 18A MESSENGER image from 18,000 km showing a region about 500 km across (2008) (from Space exploration)
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Image 19Gabbard diagram of almost 300 pieces of debris from the disintegration of the five-month-old third stage of the Chinese Long March 4 booster on 11 March 2000 (from Space debris)
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Image 20Astronaut Piers Sellers during the third spacewalk of STS-121, a demonstration of orbiter heat shield repair techniques (from Outline of space science)
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Image 21Infographic showing the space debris situation in different kinds of orbits around Earth (from Space debris)
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Image 22The International Space Station is an orbiting laboratory for space applications and habitability. Visible in the background is yellow-green airglow of Earth's ionosphere and the interstellar field of the Milky Way. (from Outer space)
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Image 23The distribution of ionized hydrogen (known by astronomers as H II from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earth's northern hemisphere as observed with the Wisconsin Hα Mapper (Haffner et al. 2003) harv error: no target: CITEREFHaffnerReynoldsTufteMadsen2003 (help). (from Interstellar medium)
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Image 24Bow shock formed by the magnetosphere of the young star LL Orionis (center) as it collides with the Orion Nebula flow
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Image 25The Long Duration Exposure Facility (LDEF) is an important source of information on small-particle space debris. (from Space debris)
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Image 26Debris impacts on Mir's solar panels degraded their performance. The damage is most noticeable on the panel on the right, which is facing the camera with a high degree of contrast. Extensive damage to the smaller panel below is due to impact with a Progress spacecraft. (from Space debris)
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Image 27Smooth chondrite interplanetary dust particle. (from Cosmic dust)
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Image 28Growth of tracked objects in orbit and related events; efforts to manage outer space global commons have so far not reduced the debris or the growth of objects in orbit (from Space debris)
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Image 29A laser-guided observation of the Milky Way Galaxy at the Paranal Observatory in Chile in 2010 (from Outline of space science)
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Image 32Major elements of 200 stratospheric interplanetary dust particles. (from Cosmic dust)
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Image 34Concept art for a NASA Vision mission (from Space exploration)
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Image 36The diversity found in the different types and scales of astronomical objects make the field of study increasingly specialized. (from Outline of space science)
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Image 37The original Magdeburg hemispheres (left) used to demonstrate Otto von Guericke's vacuum pump (right)
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Image 38View of an orbital debris hole made in the panel of the Solar Max satellite. (from Space debris)
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Image 40Vanguard 1 is expected to remain in orbit for 240 years. (from Space debris)
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Image 41NASA computer-generated image of debris objects in Earth orbit, c. 2005. (from Space debris)
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Image 42A micrometeoroid left this crater on the surface of Space Shuttle Challenger's front window on STS-7. (from Space debris)
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Image 44For the first time, the NASA / ESA / Canadian Space Agency / James Webb Space Telescope has observed the chemical signature of carbon-rich dust grains at redshift z ≈ 7, which is roughly equivalent to one billion years after the birth of the Universe, this observation suggests exciting avenues of investigation into both the production of cosmic dust and the earliest stellar populations in our Universe. (from Cosmic dust)
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Image 45Map showing the Sun located near the edge of the Local Interstellar Cloud and Alpha Centauri about 4 light-years away in the neighboring G-Cloud complex (from Interstellar medium)
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Image 47Apollo CSM in lunar orbit (from Space exploration)
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Image 48Large-scale matter distribution in a cubic section of the universe. The blue fiber-like structures represent the matter, and the empty regions in between represent the cosmic voids of the intergalactic medium (from Outer space)
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Image 50Model of Vostok spacecraft (from Space exploration)
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Image 51Near-Earth space showing the low-Earth (blue), medium Earth (green), and high Earth (red) orbits. The last extends beyond the radius of geosynchronous orbits (from Outer space)
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Image 52Illustration of a satellite breaking up into multiple pieces at higher altitudes. (from Space debris)
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Image 54Perseverance's backshell sitting upright on the surface of Jezero Crater (from Space debris)
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Image 55Artist's impression of dust formation around a supernova explosion. (from Cosmic dust)
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Image 56Atmospheric attenuation in dB/km as a function of frequency over the EHF band. Peaks in absorption at specific frequencies are a problem, due to atmosphere constituents such as water vapor (H2O) and carbon dioxide (CO2). (from Interstellar medium)
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Image 57This light-year-long knot of interstellar gas and dust resembles a caterpillar. (from Interstellar medium)
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Image 58Known orbit planes of Fengyun-1C debris one month after the weather satellite's disintegration by the Chinese ASAT (from Space debris)
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Image 60Cosmic dust of the Andromeda Galaxy as revealed in infrared light by the Spitzer Space Telescope. (from Cosmic dust)
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Image 61Earth and the Moon as seen from cislunar space on the 2022 Artemis 1 mission (from Outer space)
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Image 62Spatial density of space debris by altitude according to ESA MASTER-2001, without debris from the Chinese ASAT and 2009 collision events (from Space debris)
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Image 63Because of the hazards of a vacuum, astronauts must wear a pressurized space suit while outside their spacecraft.
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Image 64Illustration of Earth's atmosphere gradual transition into outer space (from Outer space)
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Image 65Cosmic dust of the Horsehead Nebula as revealed by the Hubble Space Telescope. (from Cosmic dust)
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Image 66Timeline of the expansion of the universe, where visible space is represented by the circular sections. At left, a dramatic expansion occurs in the inflationary epoch, and at the center, the expansion accelerates. Neither time nor size are to scale. (from Outer space)
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Image 67Debris density in low Earth orbit (from Space debris)
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Image 68A computer-generated map of objects orbiting Earth, as of 2005. About 95% are debris, not working artificial satellites (from Outer space)
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Image 69Astronomers used the James Webb Space Telescope to image the warm dust around a nearby young star, Fomalhaut, in order to study the first asteroid belt ever seen outside of the Solar System in infrared light. (from Cosmic dust)
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Image 71Buzz Aldrin taking a core sample of the Moon during the Apollo 11 mission (from Space exploration)
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Image 72Spent upper stage of a Delta II rocket, photographed by the XSS 10 satellite (from Space debris)
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Image 73The sparse plasma (blue) and dust (white) in the tail of comet Hale–Bopp are being shaped by pressure from solar radiation and the solar wind, respectively.
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Image 74Reconstruction of solar activity over 11,400 years. Period of equally high activity over 8,000 years ago marked. (from Space climate)
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Image 76Spatial density of LEO space debris by altitude, according to 2011 a NASA report to the United Nations Office for Outer Space Affairs (from Space debris)
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Image 77A wide field view of outer space as seen from Earth's surface at night. The interplanetary dust cloud is visible as the horizontal band of zodiacal light, including the false dawn (edges) and gegenschein (center), which is visually crossed by the Milky Way (from Outer space)
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Image 78First television image of Earth from space, taken by TIROS-1 (1960) (from Space exploration)
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Image 79Space Shuttle Endeavour had a major impact on its radiator during STS-118. The entry hole is about 5.5 mm (0.22 in), and the exit hole is twice as large. (from Space debris)
Did you know (auto-generated)
![](https://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Nuvola_apps_filetypes.svg/47px-Nuvola_apps_filetypes.svg.png)
- ... that, for the Space 220 Restaurant, Disney reached out to NASA engineers to understand what a space elevator might look like?
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- ... that the space industry of India has supported the launch of more than 100 domestic satellites and more than 300 foreign satellites?
- ... that Nature's Fynd, producer of microbe-based meat substitutes, is working with NASA to develop a bioreactor for use in space travel?
- ... that Louis W. Roberts was among the highest ranking African-American space program staff at NASA while the Apollo program was underway?
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Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction