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Meaning
  1. 1
    English · JMdict
    absolute magnitude
  2. 2
    English · Wikipedia

    Absolute magnitude is the measure of intrinsic brightness of a celestial object. It is the hypothetical apparent magnitude of an object at a standard distance of exactly 10 parsecs (32.6 light years) from the observer, assuming no astronomical extinction of starlight. This places the objects on a common basis and allows the true energy output of astronomical objects to be compared without the distortion introduced by distance. As with all astronomical magnitudes, the absolute magnitude can be specified for different wavelength intervals; for stars the most commonly quoted absolute magnitude is the absolute visual magnitude, which uses only the visual (V) band of the spectrum (UBV system). Also commonly used is the absolute bolometric magnitude, which is the total luminosity expressed in magnitude units that takes into account energy radiated at all wavelengths, whether visible or not. The brighter the celestial object the smaller its absolute magnitude. The magnitude scale extends downward through the positive numbers and into the negative numbers as brightness increases. A difference of 1.0 in absolute magnitude corresponds to a ratio of 2.512 ≈ 100.4 of absolute brightness. Therefore, a star of magnitude -2 is 100 (or 2.5125) times brighter than a star of magnitude +3. The Milky Way, for example, has an absolute magnitude of about −20.5, so a quasar with an absolute magnitude of −25.5 is 100 times brighter than the Milky Way. If this particular quasar and the Milky Way could be seen side by side at the same distance of one parsec and the Milky Way's stars reduced to a single point, the quasar would be 5 magnitudes (or 100 times) brighter than the Milky Way. Similarly, Canopus has an absolute visual magnitude of about −5.5, whereas Ross 248 has an absolute visual magnitude of +14.8, for a difference of about 20 magnitudes, i.e. Canopus would be seen as about 20 magnitudes brighter; stated another way, Canopus emits more than 100 million (108) times more visual power than Ross 248.

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