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In astronomy, surface brightness (SB) quantifies the apparent brightness or flux density per unit angular area of a spatially extended object such as a galaxy or nebula, or of the night sky background. An object's surface brightness depends on its surface luminosity density, i.e., its luminosity emitted per unit surface area.
Apparent magnitude (m) is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity , its distance, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer.
Prior to photographic methods to determine magnitude, the brightness of celestial objects was determined by visual photometric methods.This was simply achieved with the human eye by compared the brightness of an astronomical object with other nearby objects of known or fixed magnitude: especially regarding stars, planets and other planetary objects in the Solar System, variable stars [1] and ...
Apparent magnitude, the brightness of an object as it appears in the night sky. Absolute magnitude, which measures the luminosity of an object (or reflected light for non-luminous objects like asteroids); it is the object's apparent magnitude as seen from a specific distance, conventionally 10 parsecs (32.6 light years).
The luminosity is calculated by multiplying the galaxy's apparent brightness by , where is its distance from Earth, and the spectral-line width is measured using long-slit spectroscopy. A series of collaborative catalogs of galaxy peculiar velocity values called CosmicFlow uses Tully–Fisher analysis; the Cosmicflow-4 catalog has reached 10000 ...
As defined by the US Federal Glossary of Telecommunication Terms , "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light. [3] Brightness is an antonym of "dimness" or "dullness". With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude.
An object's surface brightness is its brightness per unit solid angle as seen in projection on the sky, and measurement of surface brightness is known as surface photometry. [9] A common application would be measurement of a galaxy's surface brightness profile, meaning its surface brightness as a function of distance from the galaxy's center.
Once the period-luminosity relation is calibrated, the luminosity of a given Cepheid whose period is known can be established. Their distance is then found from their apparent brightness. The period-luminosity relation has been calibrated by many astronomers throughout the twentieth century, beginning with Hertzsprung. [25]