Star
The effective temperature of a star is the temperature of a black body with the same luminosity per surface area as the star and is defined according to the Stefan–Boltzmann law . Notice that the total (bolometric) luminosity of a star is then, where is the stellar radius. The definition of the stellar radius is obviously not straightforward. More rigorously the effective temperature corresponds to the temperature at the radius that is defined by the Rosseland optical depth. The effective temperature and the bolometric luminosity are the two fundamental physical parameters needed to place a star on the Hertzsprung–Russell diagram. Both effective temperature and bolometric luminosity actually depend on the chemical composition of a star.
The effective temperature of our Sun is around 5780 kelvin (K). Stars actually have a temperature gradient, going from their central core up to the atmosphere. The "core temperature" of the sun—the temperature at the centre of the sun where nuclear reactions take place—is estimated to be 15 000 000 K.
The color index of a star indicates its temperature from the very cool—by stellar standards, that is—red M stars that radiate heavily in the infrared to the very blue O stars that radiate largely in the ultraviolet. The effective temperature of a star indicates the amount of heat that the star radiates per unit of surface area. From the warmest surfaces to the coolest is the sequence of star types known as O, B, A, F, G, K, and M.
A red star could be a tiny red dwarf, a star of feeble energy production and a small surface or a bloated giant or even supergiant star such as Antares or Betelgeuse, either of which generates far greater energy but passes it through a surface so large that the star radiates little per unit of surface area. A star near the middle of the spectrum, such as the modest Sun or the giant Capella radiates more heat per unit of surface area than the feeble red dwarf stars or the bloated supergiants, but much less than such a white or blue star as Vega or Rigel.
Read more about this topic: Effective Temperature
Famous quotes containing the word star:
“It is the star to every wand’ring bark,
Whose worth’s unknown, although his height be taken.
Love’s not Time’s fool, though rosy lips and cheeks
Within his bending sickle’s compass come;
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom.”
—William Shakespeare (1564–1616)
“A brush had left a crooked stroke
Of what was either cloud or smoke
From north to south across the blue;
A piercing little star was through.”
—Robert Frost (1874–1963)
“What is Africa to me:
Copper sun or scarlet sea,
Jungle star or jungle track,
Strong bronzed men, or regal black
Women from whose loins I sprang
When the birds of Eden sang?”
—Countee Cullen (1903–1946)