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The effective temperature of the Sun (5778 kelvins) is the temperature a black body of the same size must have to yield the same total emissive power.. The effective temperature of a star is the temperature of a black body with the same luminosity per surface area (F Bol) as the star and is defined according to the Stefan–Boltzmann law F Bol = σT eff 4.
In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the larger the color index, the more red (or cooler) the object is.
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.
Finally, by the virial theorem, the total kinetic energy is equal to half the gravitational potential energy E G, so if the average nuclei mass is m n, then the average kinetic energy per nucleus satisfies: = = where the temperature T is averaged over the star and C is a factor of order one related to the stellar structure and can be estimated ...
Planetary equilibrium temperature differs from the global mean temperature and surface air temperature, which are measured observationally by satellites or surface-based instruments, and may be warmer than the equilibrium temperature due to the greenhouse effect.
For example, the color temperature of an A0V star is about 15000 K compared to an effective temperature of about 9500 K. [27] For most applications in astronomy (e.g., to place a star on the HR diagram or to determine the temperature of a model flux fitting an observed spectrum) the effective temperature is the quantity of interest. Various ...
Evolution of the solar luminosity, radius and effective temperature compared to the present-day Sun. After Ribas (2010) [1] The solar luminosity (L ☉) is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun.
A star like Deneb, for example, has a luminosity around 200,000 L ⊙, a spectral type of A2, and an effective temperature around 8,500 K, meaning it has a radius around 203 R ☉ (1.41 × 10 11 m). For comparison, the red supergiant Betelgeuse has a luminosity around 100,000 L ⊙ , a spectral type of M2, and a temperature around 3,500 K ...