Apparent magnitude

apparent visual magnitudemagnitudevisual magnitudemagnitudesapparent brightnessmagvisible magnitudestellar magnitudebrightnessapmag
Apparent magnitude (m) is a measure of the brightness of a star or other astronomical object as seen from the Earth's location.wikipedia
4,258 Related Articles

Sirius

Sirius BSirius superclusterDog Star
The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46.
With a visual apparent magnitude of −1.46, Sirius is almost twice as bright as Canopus, the next brightest star.

List of brightest stars

brightest starsbrightest starone of the brightest stars
The brightest stars in the night sky were said to be of first magnitude (m = 1), whereas the faintest were of sixth magnitude (m = 6), which is the limit of human visual perception (without the aid of a telescope).
This is a list of stars down to magnitude +2.50, as determined by their maximum, total, or combined visual magnitudes as viewed from Earth.

Absolute magnitude

Hbolometric magnitudeabsolute magnitude (H)
Absolute magnitude differs from apparent magnitude in that it is a measure of the intrinsic luminosity rather than the apparent brightness of a celestial object, expressed on the same reverse logarithmic scale.
An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly 10 pc, without extinction (or dimming) of its light due to absorption by interstellar matter and cosmic dust.

Magnitude (astronomy)

magnitudemagnitudesmag
The brighter an object is, the lower its magnitude.
Astronomers use two different definitions of magnitude: apparent magnitude and absolute magnitude.

First-magnitude star

first magnitude starfirst magnitudebrightest
The brightest stars in the night sky were said to be of first magnitude (m = 1), whereas the faintest were of sixth magnitude (m = 6), which is the limit of human visual perception (without the aid of a telescope).
First-magnitude stars are the brightest stars in the night sky, with apparent magnitudes lower than +1.50.

Photometry (astronomy)

photometricphotometryphotometrically
Measurement of the apparent magnitude of celestial objects is termed photometry. For example, photometry on closely separated double stars may only be able to produce a measurement of their combined light output.
When calibrated against standard stars (or other light sources) of known intensity and colour, photometers can measure the brightness or apparent magnitude of celestial objects.

N. R. Pogson

Norman Robert PogsonNorman PogsonN.R. Pogson
In 1856, Norman Robert Pogson formalized the system by defining a first magnitude star as a star that is 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today.
He introduced a mathematical scale of stellar magnitudes with the ratio of two successive magnitudes being the fifth root of one hundred (~2.512) and referred to as Pogson's ratio.

Venus

Morning Starevening starplanet Venus
The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46.
The planet's mean apparent magnitude is −4.14 with a standard deviation of 0.31.

Logarithmic scale

logarithmiclogarithmic unitLog
The magnitude scale is reverse logarithmic such that having a magnitude 5 higher than another object's means that it is 100 times dimmer.

Sun

solarSolThe Sun
What is the ratio in brightness between the Sun and the full Moon?
The Sun is by far the brightest object in the Earth's sky, with an apparent magnitude of −26.74.

Vega

Alpha Lyrae2828Botercadent
Astronomers later discovered that Polaris is slightly variable, so they switched to Vega as the standard reference star, assigning the brightness of Vega as the definition of zero magnitude at any specified wavelength.
This apparent magnitude is a numerical value that decreases in value with increasing brightness of the star.

Betelgeuse

Alpha OrionisBételgeuseα Ori
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 human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light.
It is a distinctly reddish, semiregular variable star whose apparent magnitude varies between +0.0 and +1.3, the widest range of any first-magnitude star.

Almagest

cataloghis book on astronomyMagna Syntaxis
This rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest and is generally believed to have originated with Hipparchus.

Rigel

Beta Orionisβ Ori (Rigel)β Orionis
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 human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light.
The primary has a companion star 9.5 " away with an apparent magnitude of 6.7, 400 times fainter than the primary. The companion, often referred to as Rigel B or Rigel BC, is actually a triple star system. Two stars, components B and C, can be resolved by very large telescopes. The brighter of the two is a spectroscopic binary, the components designated Ba and Bb. A fainter star, separated from the others by nearly an arc minute, might also be part of the same star system.

Brightness

brightintensitybrilliant
Apparent magnitude (m) is a measure of the brightness of a star or other astronomical object as seen from the Earth's location.
With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude.

Strömgren photometric system

Strömgren ''uvbyβ'' systemphotometryStrömgren
Photometric measurements are made in various ultraviolet, visible, or infrared wavelength bands, as defined by standard passband filters belonging to photometric systems such as the UBV system or the Strömgren uvbyβ system.
y magnitudes are well-correlated with Johnson-Morgan V magnitudes.

Phase curve (astronomy)

phase curvephase curvesphase function
For planets and other Solar System bodies the apparent magnitude is derived from its phase curve and the distances to the Sun and observer.
The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun.

Mars

MartianCoordinatesplanet Mars
Its apparent magnitude reaches −2.94, which is surpassed only by Jupiter, Venus, the Moon, and the Sun.

R136a1

In 1960, a group of astronomers working at the Radcliffe Observatory in Pretoria made systematic measurements of the brightness and spectra of bright stars in the Large Magellanic Cloud.

Double star

visual companiondouble starsoptical double
For example, photometry on closely separated double stars may only be able to produce a measurement of their combined light output.
Since that time, the search has been carried out thoroughly and the entire sky has been examined for double stars down to a limiting apparent magnitude of about 9.0.

SN 1006

supernova of 1006supernova that occurred in 1006 CEthe 1006 supernova
SN 1006 was a supernova that is likely the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude, and exceeding roughly sixteen times the brightness of Venus.

GRB 080319B

GRB080319B
The burst set a new record for the farthest object that was observable with the naked eye: it had a peak visual apparent magnitude of 5.8 and remained visible to human eyes for approximately 30 seconds.

Weber–Fechner law

Weber's lawWeber-Fechner lawis non-linear
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).
The eye senses brightness approximately logarithmically over a moderate range (but more like a power law over a wider range), and stellar magnitude is measured on a logarithmic scale.

Eta Carinae

η Carinaeη CarEta Carinae A
Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel marking the start of the Great Eruption.

Canopus

Alpha Carinaeα Carinaea first magnitude star
Canopus' visual apparent magnitude is −0.74, and it has an absolute magnitude of −5.71.