The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. The brighter the object appears, the lower the numerical value of its magnitude. STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... The eight planets and three dwarf planets of the Solar System. ... Various meters Measurement is the estimation of a physical quantity such as length, temperature, or time. ... Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. ...

Explanation

The scale upon which magnitude is now measured has its origin in the Hellenistic practice of dividing those stars visible to the naked eye into six magnitudes. The brightest stars were said to be of first magnitude (m = 1), while the faintest were of sixth magnitude (m = 6), the limit of human visual perception (without the aid of a telescope). Each grade of magnitude was considered to be twice the brightness of the following grade (a logarithmic scale). This somewhat crude method of indicating the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This original system did not measure the magnitude of the Sun. The Hellenistic period of Greek history was the period between the death of Alexander the Great in 323 BC and the annexation of the Greek peninsula and islands by Rome in 146 BC. Although the establishment of Roman rule did not break the continuity of Hellenistic society and culture, which... Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin: wise man or knowing man) under the family Hominidae (the great apes). ... This article or section does not cite its references or sources. ... A telescope (from the Greek tele = far and skopein = to look or see; teleskopos = far-seeing) is an instrument designed for the observation of remote objects. ... A logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. ... A medieval artists rendition of Claudius Ptolemaeus Claudius Ptolemaeus (Greek: ; c. ... Almagest is the Latin form of the Arabic name (al-kitabu-l-mijisti, i. ... Hipparchus. ... The Sun is the star at the center of the Solar System. ...

In 1856, Pogson formalized the system by defining a typical first magnitude star as a star that is 100 times as bright as a typical sixth magnitude star; thus, a first magnitude star is about 2.512 times as bright as a second magnitude star. The fifth root of 100, an irrational number, is known as Pogson's Ratio^[1]. Pogson's scale was originally fixed by assigning Polaris a magnitude of 2. Astronomers later discovered that Polaris is slightly variable, so they first switched to Vega as the standard reference star, and then switched to using tabulated zero points for the measured fluxes^[2]. The magnitude depends on the wavelength band (see below). 1856 was a leap year starting on Tuesday (see link for calendar). ... Norman Robert Pogson (March 23, 1829 – June 23, 1891) was a British astronomer. ... In mathematics, an irrational number is any real number that is not a rational number, i. ... Polaris (α UMi / α Ursae Minoris / Alpha Ursae Minoris), more commonly known as The North Star or simply North Star, is the brightest star in the constellation Ursa Minor. ... Vega (α Lyr / α Lyrae / Alpha Lyrae) is the brightest star in the constellation Lyra, and the fifth brightest star in the sky. ...

The modern system is no longer limited to 6 magnitudes or only to visible light. Very bright objects have negative magnitudes. For example, Sirius, the brightest star of the celestial sphere, has an apparent magnitude of −1.46. The modern scale includes the Moon and the Sun; the full Moon has an apparent magnitude of −12.6 and the Sun has an apparent magnitude of −26.73. The Hubble Space Telescope has located stars with magnitudes of 30 at visible wavelengths and the Keck telescopes have located similarly faint stars in the infrared. For information on Sirius satellite radio, see Sirius Satellite Radio. ... The celestial sphere is divided by the celestial equator. ... Apparent magnitude: up to -12. ... The Sun is the star at the center of the Solar System. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The W. M. Keck Observatory is home to the two largest optical/near-infrared telescopes at the 4,145 meter (13,600 ft) summit of Mauna Kea in Hawaii. ...

These are only approximate values at visible wavelengths (in reality the values depend on the precise bandpass used) — see airglow for more details of telescope sensitivity. The Sun is the star at the center of the Solar System. ... Apparent magnitude: up to -12. ... Satellite flare is the phenomenon caused by the reflective surfaces many satellites have today. ... (*min temperature refers to cloud tops only) Atmospheric characteristics Atmospheric pressure 9. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Adjectives: Jovian Atmosphere Surface pressure: 20–200 kPa[4] (cloud layer) Composition: ~86% H2 ~13% Helium 0. ... This article is about planet. ... For information on Sirius satellite radio, see Sirius Satellite Radio. ... Canopus (α Car / α Carinae / Alpha Carinae) is the brightest star in the southern constellation of Carina, and the second brightest star in the sky, with a visual magnitude of −0. ... Vega (α Lyr / α Lyrae / Alpha Lyrae) is the brightest star in the constellation Lyra, and the fifth brightest star in the sky. ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... Note: This article contains special characters. ... This article or section does not adequately cite its references or sources. ... Adjectives: Uranian Atmosphere Surface pressure: 120 kPa (at the cloud level) Composition: 83% Hydrogen 15% Helium 1. ... STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... Spectral type: G[8] Absolute magnitude: 3. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... Iapetus (eye-ap-É™-tÉ™s, IPA , Greek Ιαπετός) is the third-largest moon of Saturn, discovered by Giovanni Domenico Cassini in 1671. ... Artists impression of quasar GB1508 A quasar (contraction of QUASi-stellAR radio source) is an astronomical source of electromagnetic energy, including light, which shows a very high redshift. ... Adjectives: Plutonian Atmosphere Surface pressure: 0. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The Overwhelmingly Large Telescope (OWL) is a conceptual design by the European Southern Observatory organization for a telescope which was intended to have a single aperture of 100 meters in diameter, but was later scaled down to a 60 meter diameter telescope. ... Bright stars can be bright because they produce more light, because they are closer to us, or both. ... The airglow is the very weak emission of visible light by the earths atmosphere, which means that the night sky is never completely dark. ...

As the amount of light received actually depends on the thickness of the atmosphere in the line of sight to the object, the apparent magnitudes are normalized to the value it would have outside the atmosphere. The dimmer an object appears, the higher its apparent magnitude. Note that apparent brightness is not equal to actual brightness — an extremely bright object may appear quite dim, if it is far away. The rate at which apparent brightness changes, as the distance from an object increases, is calculated by the inverse-square law (at cosmological distance scales, this is no longer quite true because of the curvature of space). The absolute magnitude, M, of a star or galaxy is the apparent magnitude it would have if it were 10 parsecs (~ 32 light years) away; that of a planet (or other solar system body) is the apparent magnitude it would have if it were 1 astronomical unit away from both the Sun and Earth. The absolute magnitude of the Sun is 4.83 in the V band (yellow) and 5.48 in the B band (blue). Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... A calculation is a deliberate process for transforming one or more inputs into one or more results. ... This diagram shows how the law works. ... Two-dimensional visualisation of space-time distortion. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant. ... Stellar parallax motion The parsec (symbol pc) is a unit of length used in astronomy. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... The astronomical unit (AU or au or a. ... The Sun is the star at the center of the Solar System. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ...

The apparent magnitude in the band x can be defined as (noting that )

where is the observed flux in the band x, and is a constant that depends on the units of the flux and the band. The constant is defined in Aller et al 1982 for the most commonly used system. flux in science and mathematics. ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ...

The variation in brightness between two luminous objects can be calculated another way by subtracting the magnitude number of the brighter object from the magnitude number of the fainter object, then using the difference as an exponent for the base number 2.512; that is to say (m_f − m_b = x; and 2.512^x = variation in brightness).

Example 1

What is the difference in brightness between the Sun and the full moon?

m_f − m_b = x

2.512^x = variation in brightness

The apparent magnitude of the Sun is -26.73, and the apparent magnitude of the full moon is -12.6. The full moon is the fainter of the two objects, while the Sun is the brighter.

Difference in brightness

x = m_f − m_b

x = − 12.6 − − 26.73 = 14.13

x = 14.13

Variation in Brightness

v_b = 2.512^x

v_b = 2.512¹4.13

v_b = 449,032.16

variation in brightness = 449,032.16

In terms of apparent magnitude, the Sun is more than 449,032 times brighter than the full moon. This is a good reason to avoid looking directly at the Sun, even during the non-total phases of a solar eclipse. (Viewing the completely eclipsed Sun is safe, but it only stays completely eclipsed for a very short period of time.)

Example 2

What is the difference in brightness between Sirius and Polaris?

m_f − m_b = x

2.512^x = variation in brightness

The apparent magnitude of Sirius is -1.44, and the apparent magnitude of Polaris is 1.97. Polaris is the fainter of the two stars, while Sirius is the brighter.

Difference in brightness

x = m_f − m_b

x = 1.97 − − 1.44 = 3.41

x = 3.41

Variation in brightness

v_b = 2.512^x

v_b = 2.512^3.41

v_b = 23.124

In terms of apparent magnitude, Sirius is 23.124 times brighter than Polaris the North Star.

The second thing to notice is that the scale is logarithmic: the relative brightness of two objects is determined by the difference of their magnitudes. For example, a difference of 3.2 means that one object is about 19 times as bright as the other, because Pogson's ratio raised to the power 3.2 is 19.054607... A common misconception is that the logarithmic nature of the scale is due to the fact that the human eye itself has a logarithmic response. In Pogson's time this was thought to be true (see Weber-Fechner law), but it is now believed that the response is a power law (see Stevens' power law)^[3]. Above is the graph plots of Logarithms to various bases: is to base e, is to base 10, and is to base 1. ... A human eye. ... The Weber - Fechner law attempts to describe the relationship between the physical magnitudes of stimuli and human perception of the intensity of stimuli. ... See Also: Watt In physics, a power law relationship between two scalar quantities x and y is any such that the relationship can be written as where a (the constant of proportionality) and k (the exponent of the power law) are constants. ... Stevens power law relates the intensity of a stimulus to its perceived strength. ...

Magnitude is complicated by the fact that light is not monochromatic. The sensitivity of a light detector varies according to the wavelength of the light, and the way in which it varies depends on the type of light detector. For this reason, it is necessary to specify how the magnitude is measured in order for the value to be meaningful. For this purpose the UBV system is widely used, in which the magnitude is measured in three different wavelength bands: U (centred at about 350 nm, in the near ultraviolet), B (about 435 nm, in the blue region) and V (about 555 nm, in the middle of the human visual range in daylight). The V band was chosen for spectral purposes and gives magnitudes closely corresponding to those seen by the light-adapted human eye, and when an apparent magnitude is given without any further qualification, it is usually the V magnitude that is meant, more or less the same as visual magnitude. Something which is monochromatic has a single color. ... UBV photometric system, also called the Johnson system (or Johnson-Morgan system), is a wide band photometric system for classifying stars according to their colors. ... UV redirects here. ...

Since cooler stars, such as red giants and red dwarfs, emit little energy in the blue and UV regions of the spectrum their power is often under-represented by the UBV scale. Indeed, some L and T class stars have an estimated magnitude of well over 100, since they emit extremely little visible light, but are strongest in infrared. Cross section of a red giant showing nucleosynthesis and elements formed According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... An artists impression of a planet in orbit around a red dwarf According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... Image of two girls in mid-infrared (thermal) light (false-color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ...

Measures of magnitude need cautious treatment and it is extremely important to measure like with like. On early 20th-century and older orthochromatic (blue-sensitive) photographic film, the relative brightnesses of the blue supergiant Rigel and the red supergiant Betelgeuse irregular variable star (at maximum) are reversed compared to what our eyes see since this archaic film is more sensitive to blue light than it is to red light. Magnitudes obtained from this method are known as photographic magnitudes, and are now considered obsolete. This article or section does not cite its references or sources. ... Supergiants are the most massive stars. ... Rigel (pronounced ) (β Orionis) is the brightest star in the constellation Orion and the seventh brightest star in the sky, with visual magnitude 0. ... Betelgeuse (Alpha (α) Orionis) is a semiregular variable star located 427 light-years away [1]. It is the second brightest star in the constellation Orion, and the ninth brightest star in the night sky. ... Before the advent of photometers which accurately measure the brightness of astronomical objects, the apparent magnitude of an object was obtained by taking a picture of it with a camera. ...

For objects within our Galaxy with a given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object. This relationship does not apply for objects at very great distances (far beyond our galaxy), since a correction for General Relativity must then be taken into account due to the non-Euclidean nature of space. In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... General relativity (GR) [also called the general theory of relativity (GTR) and general relativity theory (GRT)] is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ...

See also

• Absolute magnitude
• List of brightest stars
• List of nearest bright stars
• List of nearest stars

In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... Bright stars can be bright because they produce more light, because they are closer to us, or both. ... The list of nearest bright stars is a table of stars found near the Sun that have an absolute magnitude of +8. ... This list of the nearest stars to Earth is ordered by increasing distance out to a maximum of 5 parsecs (16. ...

References