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This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a ...
In photometry, luminous energy is the perceived energy of light.This is sometimes called the quantity of light. [1] Luminous energy is not the same as radiant energy, the corresponding objective physical quantity.
In astronomy, values for luminosity are often given in the terms of the luminosity of the Sun, L ⊙. Luminosity can also be given in terms of the astronomical magnitude system: the absolute bolometric magnitude ( M bol ) of an object is a logarithmic measure of its total energy emission rate, while absolute magnitude is a logarithmic measure ...
As an example, if one uses a lens to form an image that is smaller than the source object, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the image plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens.
The small excess fractional value comes from the slight mismatch between the definition of the lumen and the peak of the luminosity function. The lumen is defined to be unity for a radiant energy of 1/683 W at a frequency of 540 THz , which corresponds to a standard air wavelength of 555.016 nm rather than 555 nm , which is the peak of the ...
Luminous blue variables are by definition more luminous than most stars and also more massive, but within a very wide range. The most luminous are more than a million L ☉ (Eta Carinae reaches 4.6 million) and have masses approaching, possibly exceeding, 100 M ☉.
Prior to the definition of the candela, a variety of units for luminous intensity were used in various countries. These were typically based on the brightness of the flame from a "standard candle" of defined composition, or the brightness of an incandescent filament of specific design.
For planets and asteroids, a definition of absolute magnitude that is more meaningful for non-stellar objects is used. The absolute magnitude, commonly called H {\displaystyle H} , is defined as the apparent magnitude that the object would have if it were one astronomical unit (AU) from both the Sun and the observer, and in conditions of ideal ...