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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. One nominal solar luminosity is defined by the International Astronomical Union to be 3.828 × 10 26 W. [2 ...
Since the Sun's luminosity is the standard, comparing these parameters with the Sun's apparent magnitude and distance is the easiest way to remember how to convert between them, although officially, zero point values are defined by the IAU. The magnitude of a star, a unitless measure, is a logarithmic scale of observed visible brightness.
For the purpose of measurement, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun. [41] By this measure, the Sun is a near-perfect sphere with an oblateness estimated at 9 millionths, [42] [43] [44] which means that its polar diameter differs from its ...
Because Solar System bodies are illuminated by the Sun, their brightness varies as a function of illumination conditions, described by the phase angle. This relationship is referred to as the phase curve. The absolute magnitude is the brightness at phase angle zero, an arrangement known as opposition, from a distance of one AU.
maximum brightness [42] when illuminated as a crescent −4.14: planet Venus: seen from Earth mean brightness [42] −4: Faintest objects observable during the day with naked eye when Sun is high. An astronomical object casts human-visible shadows when its apparent magnitude is equal to or lower than −4 [43] −3.99: star Epsilon Canis Majoris
If this object were 10 parsecs away from Earth it would appear nearly as bright in the sky as the Sun (apparent magnitude −26.744). This quasar's luminosity is, therefore, about 2 trillion (10 12) times that of the Sun, or about 100 times that of the total light of average large galaxies like our Milky Way. (Note that quasars often vary ...
At astronomical twilight, the Sun is between –12° and –18°. When the Sun's depth is more than 18°, the sky generally attains its maximum darkness. Sources of the night sky's intrinsic brightness include airglow, indirect scattering of sunlight, scattering of starlight, and light pollution. [1]
The apparent magnitude (m) is the brightness of an object and depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness. The absolute magnitude ( M ) describes the intrinsic luminosity emitted by an object and is defined to be equal to the apparent magnitude that the object would have if it were ...