The main difference between absolute and apparent magnitude is that absolute magnitude does not take into account the size of the celestial body and the point from where it is viewed. Absolute magnitude helps us to know the luminosity of any celestial body from a fixed distance of ten parsecs (one parsec equals 3.25 light-years). The two standards which are in use are the absolute magnitude and apparent magnitude. Later, two standards were developed from the earlier scale referred by Hipparchus to determine the magnitude of the luminosity of the celestial bodies. The scale for standardizing the magnitude of the star was first conceptualized by Hipparchus (Turkish astronomer), thousands of years before. The factor for determining the magnitude was developed at a very early age. Either the distance from the earth or its energy level to radiate the electromagnetic wave (light) could be the factor. The reason for the varying magnitude of brightness could be many. When we look at a clear sky during the night, the entire space would be lit by the stars which appear as tiny bright colour spots.

Both radiated waves and reflected waves contribute to brightness, while luminosity only depends on the radiated waves.There is a countless number of stars present in this universe.

Brightness is measured in watt per unit area, while luminosity is measured in watt.

Luminosity is an intrinsic property, which means it is independent of the distance and other factors on the other hand, brightness is a function of both luminosity and the distance from the object.

What is the difference between luminosity and brightness? The brightness of an object follows inverse square law. Both radiated waves and reflected waves can contribute to brightness. Brightness is measured in watt per square meter. When a hollow imaginary sphere is drawn at a distance r from the center object, the area of the sphere is 4πr2.Therefore, the energy carried per unit area per unit time is L/ 4πr2. Imagine a point object of luminosity L, which means it radiates L watts per second. Brightness is formally defined as the energy carried by electromagnetic waves going through a unit area per time. The term brightness usually refers to the amount visible light. The luminosity of an object, which has a surface area A, and the surface having a uniform temperature T is given by E =σ AT4, where σ is the Stephan-Boltzmann constant and the temperature is measured in kelvin.īrightness is a term frequently used in the study of photography, astronomy and any optical phenomena. There is also a concept of spectral luminosity, which is defined as the energy radiated per unit frequency per unit time. Luminosity also corresponds to the absolute magnitude of a star, which is defined as the apparent luminosity of the visible light region in the electromagnetic spectrum. In astronomy, the luminosity of stars is measured using the unit called solar luminance (L0). Luminosity is an intrinsic property of the object. However, luminosity of an object does not depend on the distance from which it is observed. In photography, luminosity is used in the context of luminance, which is measured as the candela per unit area. Alternatively, we also can take the units as joules per second. The proper definition of luminosity is the energy radiated per unit time. In some cases, the word is used in other context than the literal meaning of the word. Luminosity is a frequent term used in fields such as photography, graphic designing and astronomy. In this article, we are going to discuss what luminosity and brightness are, their definitions, what are the calculations associated with luminosity and brightness, their applications, similarities and finally the difference between brightness and luminosity. Some of the theories of luminosity and brightness are easily understood, but some theories require some understanding of advanced mathematics and physics, these advanced theories are out of the scope of this article. Brightness and luminosity are mostly discussed with regard to light, but these theories can also be applied to any form of electromagnetic radiation. It is vital to have a good understanding in the concepts of brightness and luminosity in order to excel in such fields.

There are tremendous amounts of applications of brightness and luminosity in fields such as astronomy, physics, astrophysics, cosmology, agriculture, meteorology and even photography. Brightness and luminosity are two very important concepts of light and radiation.

Apparent brightness