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  2. Faint young Sun paradox - Wikipedia

    en.wikipedia.org/wiki/Faint_young_Sun_paradox

    The faint young Sun paradox or faint young Sun problem describes the apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the Sun's output would have been only 70 percent as intense during that epoch as it is during the modern epoch. [1]

  3. Albedo - Wikipedia

    en.wikipedia.org/wiki/Albedo

    Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice).

  4. Mass–luminosity relation - Wikipedia

    en.wikipedia.org/wiki/Mass–luminosity_relation

    The relationship is represented by the equation: = where L ⊙ and M ⊙ are the luminosity and mass of the Sun and 1 < a < 6. [2] The value a = 3.5 is commonly used for main-sequence stars. [ 3 ] This equation and the usual value of a = 3.5 only applies to main-sequence stars with masses 2 M ⊙ < M < 55 M ⊙ and does not apply to red giants ...

  5. Phase curve (astronomy) - Wikipedia

    en.wikipedia.org/wiki/Phase_curve_(astronomy)

    The apparent brightness of Mercury as seen from Earth is greatest at phase angle 0° (superior conjunction with the Sun) when it can reach magnitude −2.6. [14] At phase angles approaching 180° ( inferior conjunction ) the planet fades to about magnitude +5 [ 14 ] with the exact brightness depending on the phase angle at that particular ...

  6. Luminosity - Wikipedia

    en.wikipedia.org/wiki/Luminosity

    Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. [1] [2] In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a star, galaxy, or other astronomical objects. [3] [4]

  7. Variable star - Wikipedia

    en.wikipedia.org/wiki/Variable_star

    Intrinsic variables, whose luminosity actually changes periodically; for example, because the star swells and shrinks. Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes eclipses it.

  8. Michelson–Morley experiment - Wikipedia

    en.wikipedia.org/wiki/Michelson–Morley_experiment

    The theory postulates that light has always the same velocity in respect to the source. [A 28] However de Sitter noted that emitter theory predicted several optical effects that were not seen in observations of binary stars in which the light from the two stars could be measured in a spectrometer. If emission theory were correct, the light from ...

  9. Classical Cepheid variable - Wikipedia

    en.wikipedia.org/wiki/Classical_Cepheid_variable

    A classical Cepheid's luminosity is directly related to its period of variation. The longer the pulsation period, the more luminous the star. The period-luminosity relation for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of variable stars in the Magellanic Clouds. [23]