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The term outward space existed in a poem from 1842 by the English poet Lady Emmeline Stuart-Wortley called "The Maiden of Moscow", [13] but in astronomy the term outer space found its application for the first time in 1845 by Alexander von Humboldt. [14] The term was eventually popularized through the writings of H. G. Wells after 1901. [15]
The physical universe is defined as all of space and time [a] (collectively referred to as spacetime) and their contents. [10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.
[f] Six planets, seven dwarf planets, and other bodies have orbiting natural satellites, which are commonly called 'moons'. The Solar System is constantly flooded by the Sun's charged particles, the solar wind, forming the heliosphere. Around 75–90 astronomical units from the Sun, [g] the solar wind is halted, resulting in the heliopause.
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.
Cosmic dust – also called extraterrestrial dust, space dust, or star dust – is dust that occurs in outer space or has fallen onto Earth. [ 1 ] [ 2 ] Most cosmic dust particles measure between a few molecules and 0.1 mm (100 μm ), such as micrometeoroids (<30 μm) and meteoroids (>30 μm). [ 3 ]
X-ray jet made from a supermassive black hole found by NASA's Chandra X-ray Observatory, made visible by light from the early Universe X-ray astronomy uses X-ray wavelengths . Typically, X-ray radiation is produced by synchrotron emission (the result of electrons orbiting magnetic field lines), thermal emission from thin gases above 10 7 (10 ...
The eight planets of the Solar System with size to scale (up to down, left to right): Saturn, Jupiter, Uranus, Neptune (outer planets), Earth, Venus, Mars, and Mercury (inner planets) A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. [1]
The observable universe contains as many as an estimated 2 trillion galaxies [36] [37] [38] and, overall, as many as an estimated 10 24 stars [39] [40] – more stars (and, potentially, Earth-like planets) than all the grains of beach sand on planet Earth. [41] [42] [43] Other estimates are in the hundreds of billions rather than trillions.