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Main-sequence stars vary in surface temperature from approximately 2,000 to 50,000 K, whereas more-evolved stars – in particular, newly-formed white dwarfs – can have surface temperatures above 100,000 K. [3] Physically, the classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest.
Hertzsprung noted that stars described with narrow lines tended to have smaller proper motions than the others of the same spectral classification. He took this as an indication of greater luminosity for the narrow-line stars, and computed secular parallaxes for several groups of these, allowing him to estimate their absolute magnitude. [2]
Ordinary stars are composed mainly of the light elements hydrogen and helium.They also contain a small proportion of heavier elements, and this fraction is referred to as a star's metallicity (even if the elements are not metals in the traditional sense), [3] denoted [m/H] and expressed on a logarithmic scale where zero is the Sun's metallicity.
The Sun, a spectral class G2V main-sequence star; The inner Solar System and the terrestrial planets. 2021 PH27; Mercury. Mercury-crossing minor planets; Venus. Venus-crossing minor planets. 524522 Zoozve, Venus' quasi-satellite; Earth. Moon; Near-Earth asteroids (including 99942 Apophis) Earth trojan (2010 TK 7) Earth-crosser asteroids. Earth ...
A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
The study of stars and stellar evolution is fundamental to our understanding of the Universe. The astrophysics of stars has been determined through observation and theoretical understanding; and from computer simulations of the interior. [100] Star formation occurs in dense regions of dust and gas, known as giant molecular clouds.
The Sun is the brightest star as viewed from Earth, at −26.78 mag. The second brightest is Sirius at −1.46 mag. For comparison, the brightest non-stellar objects in the Solar System have maximum brightnesses of: the Moon −12.7 mag [1] Venus −4.92 mag; Jupiter −2.94 mag; Mars −2.94 mag; Mercury −2.48 mag; Saturn −0.55 mag [2]
Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right Chart of stellar evolution A mass-radius plot ...