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Comet Lovejoy and Jupiter, a giant gas planet; The Sun; Sirius A with Sirius B, a white dwarf; the Crab Nebula, a remnant supernova; A black hole (artist concept); Vela Pulsar, a rotating neutron star; M80, a globular cluster, and the Pleiades, an open star cluster; The Whirlpool galaxy and Abell 2744, a galaxy cluster; Superclusters, galactic ...
The evolving star may eject some portion of its atmosphere to form a nebula, either steadily to form a planetary nebula or in a supernova explosion that leaves a remnant. Depending on the initial mass of the star and the presence or absence of a companion, a star may spend the last part of its life as a compact object ; either a white dwarf ...
Any astronomical object that is not an individual star or an object within the Earth's Solar System. The classification is used mostly in amateur observational astronomy to distinguish faint objects in the night sky such as star clusters, nebulae, and galaxies. degenerate star A star composed of degenerate matter, e.g. a white dwarf or a ...
This serves as a working definition even though there is no single agreed-upon definition of what constitutes a void. The matter density value used for describing the cosmic mean density is usually based on a ratio of the number of galaxies per unit volume rather than the total mass of the matter contained in a unit volume. [9]
It had been conjectured that the fixed stars were much farther away than the planets. Sun: Star 3rd century BC — 1609 380 Earth radii (very inaccurate, true=16000 Earth radii) Aristarchus of Samos made a measurement of the distance of the Sun from the Earth in relation to the distance of the Moon from the Earth. The distance to the Moon was ...
Many TNOs are often just assumed to have Pluto's density of 2.0 g/cm 3, but it is just as likely that they have a comet-like density of only 0.5 g/cm 3. [ 4 ] For example, if a TNO is incorrectly assumed to have a mass of 3.59 × 10 20 kg based on a radius of 350 km with a density of 2 g/cm 3 but is later discovered to have a radius of only 175 ...
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.
It is a function of the star's luminosity, its distance from Earth, the extinction effect of interstellar dust and gas, and the altering of the star's light as it passes through Earth's atmosphere. Intrinsic or absolute magnitude is directly related to a star's luminosity, and is the apparent magnitude a star would be if the distance between ...