# Luminosity

luminousbolometric luminosityluminositiesbolometric luminositiesbolometricabsolute luminositiesbrightnessbrightnessesbrilliancefaint
In astronomy, luminosity is the total amount of energy emitted per unit of time by a star, galaxy, or other astronomical object.wikipedia
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### Absolute magnitude

Hbolometric magnitudeabsolute magnitude (H)
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 of the luminosity within some specific wavelength range or filter band.
Absolute magnitude is a measure of the luminosity of a celestial object, on a logarithmic astronomical magnitude scale.

### Solar luminosity

luminosity of the SunSun's luminosityluminosity
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 of the luminosity within some specific wavelength range or filter band.
The solar luminosity, is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun.

### Magnitude (astronomy)

magnitudemagnitudesmag
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 of the luminosity within some specific wavelength range or filter band.
Apparent magnitude depends on an object's intrinsic luminosity, its distance, and the extinction reducing its brightness.

### Wolf–Rayet star

Wolf-RayetWolf–RayetWolf-Rayet star
In some cases, the process of estimation is extreme, with luminosities being calculated when less than 1% of the energy output is observed, for example with a hot Wolf-Rayet star observed only in the infra-red.
All Wolf–Rayet stars are highly luminous objects due to their high temperatures—thousands of times the bolometric luminosity of the Sun for the CSPNe, for the Population I WR stars, to for the WNh stars—although not exceptionally bright visually since most of their radiation output is in the ultraviolet.

### Astronomy

astronomicalastronomerastronomers
In astronomy, luminosity is the total amount of energy emitted per unit of time by a star, galaxy, or other astronomical object.
Their emissions are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition.

### Hertzsprung–Russell diagram

color-magnitude diagramHR diagramcolor magnitude diagram
In the Hertzsprung–Russell diagram, the x-axis represents temperature or spectral type while the y-axis represents luminosity or magnitude.
The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications or effective temperatures.

### Betelgeuse

α OriBetelg'''euseBetelgeuse mass loss
Certain stars like Deneb and Betelgeuse are found above and to the right of the main sequence, more luminous or cooler than their equivalents on the main sequence.
It is distinctly reddish, and is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first-magnitude star.

### Stellar classification

spectral typeK-typeG-type
In the current system of stellar classification, stars are grouped according to temperature, with the massive, very young and energetic Class O stars boasting temperatures in excess of 30,000 K while the less massive, typically older Class M stars exhibit temperatures less than 3,500 K. Because luminosity is proportional to temperature to the fourth power, the large variation in stellar temperatures produces an even vaster variation in stellar luminosity.
This two-dimensional (temperature and luminosity) classification scheme is based on spectral lines sensitive to stellar temperature and surface gravity, which is related to luminosity (whilst the Harvard classification is based on just surface temperature).

### Bolometric correction

bolometric
Bolometric luminosities can also be calculated using a bolometric correction to a luminosity in a particular passband.
IAU 2015 Resolution B2 proposed an absolute bolometric magnitude scale where corresponds to luminosity 3.0128 W, with the zero point luminosity chosen such that the Sun (with nominal luminosity 3.828 W) corresponds to absolute bolometric magnitude.

### R136a1

An example is R136a1, over 50,000 K and shining at over 8,000,000 L ⊙ (mostly in the UV), it is only 35 R ⊙.
Its Wide Field and Planetary Camera (WFPC) resolved R136a into at least 12 components and showed that R136 contained over 200 highly luminous stars.

### Main sequence

main-sequencemain sequence dwarfmain-sequence star
The vast majority of stars are found along the main sequence with blue Class O stars found at the top left of the chart while red Class M stars fall to the bottom right. For stars on the main sequence, luminosity is also related to mass:
He published the first plots of color versus luminosity for these stars.

### Effective temperature

surface temperatureeffective (surface) temperaturetemperature
A star's luminosity can be determined from two stellar characteristics: size and effective temperature.
Take the case of a planet at a distance from the star, of luminosity.

### Deneb

Alpha Cygniα CygAlpha Cygni (Deneb)
Certain stars like Deneb and Betelgeuse are found above and to the right of the main sequence, more luminous or cooler than their equivalents on the main sequence.
Deneb's absolute magnitude is currently estimated as −8.4, placing it among the most luminous stars known, with an estimated luminosity nearly 200,000 times that of the Sun.

### Apparent magnitude

apparent visual magnitudemagnitudevisual magnitude
Apparent magnitude is a logarithmic measure of apparent brightness.
Luminosity in astronomy

### O-type main-sequence star

OO-typeO-type stars
In the current system of stellar classification, stars are grouped according to temperature, with the massive, very young and energetic Class O stars boasting temperatures in excess of 30,000 K while the less massive, typically older Class M stars exhibit temperatures less than 3,500 K. Because luminosity is proportional to temperature to the fourth power, the large variation in stellar temperatures produces an even vaster variation in stellar luminosity.
Their bolometric luminosities are between.

### Mass–luminosity relation

mass-luminosity relationmass-luminosity ratiomass-luminosity relationship
For stars on the main sequence, luminosity is also related to mass:
In astrophysics, the mass–luminosity relation is an equation giving the relationship between a star's mass and its luminosity, first noted by Jakob Karl Ernst Halm.

### List of most luminous stars

most luminousmost luminous starsmost luminous stars known
List of most luminous stars
Below is a list of stars arranged in order of decreasing luminosity (increasing bolometric magnitude).

### N. R. Pogson

Norman PogsonNorman R. PogsonPogson
In 1856 Norman Pogson, noticing that photometric measurements had established first magnitude stars as being about 100 times brighter than sixth magnitude stars, formalized the Hipparchus system by creating a logarithmic scale, with every interval of one magnitude equating to a variation in brightness of 100 1/5 or roughly 2.512 times.
where m is the stellar magnitude and L is the luminosity, for stars 1 and 2.

### Vega

At present, Vega has more than twice the mass of the Sun and its bolometric luminosity is about 40 times the Sun's.

### 54 Piscium

54 Psc
It has been calculated that the star may have 76 percent of the Sun's mass and 46 percent of the luminosity.

### Photometry (astronomy)

photometricphotometryphotometrically
In 1856 Norman Pogson, noticing that photometric measurements had established first magnitude stars as being about 100 times brighter than sixth magnitude stars, formalized the Hipparchus system by creating a logarithmic scale, with every interval of one magnitude equating to a variation in brightness of 100 1/5 or roughly 2.512 times.
Photometric measurements can be combined with the inverse-square law to determine the luminosity of an object if its distance can be determined, or its distance if its luminosity is known.

### Redshift

red shiftzred-shift
For example, consider a 1 Jy signal from a radio source at a redshift of 1, at a frequency of 1.4 GHz.
Because it is usually not known how luminous objects are, measuring the redshift is easier than more direct distance measurements, so redshift is sometimes in practice converted to a crude distance measurement using Hubble's law.

### Pleione (star)

Pleione28 Tau28 Tau (Pleione)
It has a bolometric luminosity of 190 assuming a distance of roughly 120 pc.

### Stefan–Boltzmann law

lawluminosity increases with the fourth power of temperatureproportional to the fourth power
The Stefan–Boltzmann equation applied to a black body gives the value for luminosity for a black body, an idealized object which is perfectly opaque and non-reflecting:
where L is the luminosity, σ is the Stefan–Boltzmann constant, R is the stellar radius and T is the effective temperature.

### Orders of magnitude (power)

terawatt100 Watts13,759 MW
Orders of magnitude (power)