Limiting magnitude is an astronomical term which describes the faintest apparent magnitude detectable or detected by a given instrument. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value
In some cases, limiting magnitude refers to the utter threshold of detection. In general detection is the extraction of information from any clear or clouded ambient or otherwise accessible stream of information without neither support from the sender nor synchronization In more formal uses, limiting magnitude is specified along with the strength of the signal, e. g. , "10th magnitude at 20 sigma. In Probability and Statistics, the standard deviation is a measure of the dispersion of a collection of values " Sometimes limiting magnitude is qualified by the purpose of the instrument, e. g. , "10th magnitude for photometry;" this statement recognizes that a photometric detector can detect light far fainter than it can reliably measure it. Photometry is a technique of Astronomy concerned with measuring the Flux, or intensity of an Astronomical object 's Electromagnetic
The International Dark-Sky Association has been vocal in championing the cause of limiting skyglow and light pollution / photopollution. The International Dark-Sky Association ( IDA) is a US-based Non-profit organization incorporated in 1988 by founding members including an astronomer a medical Skyglow (or sky glow) is a kind of Light pollution, visible by the "glowing" effect seen in the skies over many cities and towns as a dome of light Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive Light created mainly by Humans Among other effects Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive Light created mainly by Humans Among other effects
Limiting Magnitude in Amateur Astronomy
In amateur astronomy, limiting magnitude frequently refers to the faintest stars that can be seen with the unaided eye near the zenith on clear moonless nights. Amateur astronomy, a subset of Astronomy, is a Hobby whose participants enjoy studying and observing celestial objects In broad terms the zenith is the direction pointing directly above a particular location ( Perpendicular, Orthogonal) The quantity is most often used as an overall indicator of sky quality, in that light polluted and humid areas generally have brighter limiting magnitudes than remote desert or high altitude areas.
There is even variation within metropolitan areas. For those who lives in the immediate suburbs of New York City, the limiting magnitude might be 4. The City of New York 0. This corresponds to roughly 250 visible stars, or one-tenth the number that can be perceived under perfectly dark skies. From the outer boroughs of New York City (Brooklyn, Queens, Staten Island and the Bronx), the limiting magnitude might be 3. Brooklyn (named after the Dutch town Breukelen) is one of the five boroughs of New York City. Staten Island (ˌstætənˈaɪlənd is a borough of New York City situated primarily on the island of the same name 0, suggesting that at best, only about 50 stars might be seen at any one time. From brightly-lit Midtown Manhattan, the limiting magnitude is possibly 2. Manhattan Island, in New York Harbor, is much the largest part of the Borough of Manhattan, one of the Five Boroughs which form the City of New York 0, meaning that from the heart of New York City only approximately 15 stars will be visible at any given time.
From relatively dark suburban areas, the limiting magnitude is frequently closer to 5 or somewhat fainter, but from very remote and clear sites, some amateur astronomers can see nearly as faint as 8th magnitude. Many basic observing references quote a limiting magnitude of 6, as this is the approximate limit of star maps which date from before the invention of the telescope.
Ability in this area, which requires the use of averted vision, varies substantially from observer to observer, with both youth and experience being beneficial. At higher altitudes, breathing pure oxygen is an advantage; and there is much anecdotal evidence as well that the herb bilberry can generally improve night vision. Bilberry is a name given to several species of low-growing Shrubs in the Genus Vaccinium (family Ericaceae) that bears fruits Night vision is the ability to see in a dark environment Whether by biological or technological means night vision is made possible by a combination of two approaches sufficient
Calculating the Limiting Magnitude Using a Telescope
Ignoring relatively minor complicating factors, the gain in magnitudes of a telescope is 5 * Log10(D1/D0), where D1 is the diameter of the telescope's primary light gathering component, and D0 is the diameter of the eye's dark adapted pupil. Both quantities must be measured in the same units. D0 varies from person to person but is typically 6-7mm (~1/4").
A 10-inch (D1=254mm) telescope therefore provides a gain of about 8 magnitudes beyond what could be observed without it. Thus, if one is at a site where the naked eye limiting magnitude is 5, the telescope will allow one to see stars as faint as about magnitude 13.
See also
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