Difference between revisions of "Magnitude"
m (1 revision(s)) |
|
(No difference)
| |
Revision as of 19:54, 2 May 2007
This definition page has been automatically generated. You can help ExoDictionary by expanding, updating, or correcting it. |
| This autostub has not yet had its initial copyediting proof and may contain significant formatting and even factual errors. You can improve Exodictionary by cleaning up the page markup and verifying that the definition is correct and then removing this tag. |
| This autostub has not yet had its initial categorization proof and may be categorized incorrectly. You can improve Exodictionary by removing inappropriate categories and then removing this tag. |
Magnitude
(symbol m)
</dt>
1. The relative luminance of
a celestial body. The smaller (algebraically) the number indicating magnitude,
the more luminous the body. Also called stellar magnitude. See absolute
magnitude.
</dd>
The ratio of relative luminosity of two celestial bodies differing in
magnitude by 1.0 is 2.512, the fifth root of 100.
Decrease of light by a
factor of 100 increases the stellar magnitude by 5.00; hence, the brightness
objects have negative magnitudes (Sun: -26.8; mean full moon: -12.5; Venus at
brightest: -4.3; Jupiter at opposition: -2.3; Sirius: -1.6; Vega: 0.2;
Polaris: 2.1). The faintest stars visible to the naked eye on a clear dark
night are of about the sixth magnitude (though on a perfectly black background
the limit for a single luminous point approaches the eighth magnitude). The
faintest stars visible with a telescope of aperture a (in inches) is
one approximately of magnitude <math>9 + 5 log10 a</math>. The
magnitude of the faintest stars which can be photographed with the 200-inch
telescope is about +22.7.
The expression first magnitude is often
used somewhat loosely to refer to all bodies of magnitude 1.5 or brighter,
including negative magnitudes.
</dd>
2. Amount; size; greatness. See order of
magnitude.
</dd>
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
