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Magnitude (astronomy)
 
 
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In astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
, magnitude refers to the logarithm
Logarithm

In mathematics, the logarithm of a number to a given base is the Power or exponent to which the base must be raised in order to produce the number....
ic measure of the brightness of an object, measured in a specific wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
 or passband
Passband

In brief, the passband is the range of frequencies or wavelengths that can pass through a electronic filter without being attenuated....
, usually in optical
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 or near-infrared
Infrared

Infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves ....
 wavelengths.

Origin and why bright objects are negative magnitude, dim objects positive
It traces to the Greek astronomer Hipparchus
Hipparchus

Hipparchus, the common Latinization of the Greek Hipparkhos, can mean:* Hipparchus, the ancient Greek astronomer** Hipparchic cycle, an astronomical cycle he created...
 (or the Alexandrian astronomer Ptolemy
Ptolemy

Claudius Ptolemaeus , known in English as Ptolemy , was a Roman Greek mathematics, Greek astronomy, geographer and astrologer. He lived in History of Roman Egypt, and was probably born there in a town in the Thebaid called Ptolemais Hermiou; he died in Alexandria around 168 AD....
—references vary). He classed stellar objects on how bright they appeared — the brightest were "magnitude 1", the next brightest were "magnitude 2", on down to "magnitude 6", the faintest he could see.






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In astronomy
Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
, magnitude refers to the logarithm
Logarithm

In mathematics, the logarithm of a number to a given base is the Power or exponent to which the base must be raised in order to produce the number....
ic measure of the brightness of an object, measured in a specific wavelength
Wavelength

In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek language letter lambda ....
 or passband
Passband

In brief, the passband is the range of frequencies or wavelengths that can pass through a electronic filter without being attenuated....
, usually in optical
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 or near-infrared
Infrared

Infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves ....
 wavelengths.

Origin and why bright objects are negative magnitude, dim objects positive


It traces to the Greek astronomer Hipparchus
Hipparchus

Hipparchus, the common Latinization of the Greek Hipparkhos, can mean:* Hipparchus, the ancient Greek astronomer** Hipparchic cycle, an astronomical cycle he created...
 (or the Alexandrian astronomer Ptolemy
Ptolemy

Claudius Ptolemaeus , known in English as Ptolemy , was a Roman Greek mathematics, Greek astronomy, geographer and astrologer. He lived in History of Roman Egypt, and was probably born there in a town in the Thebaid called Ptolemais Hermiou; he died in Alexandria around 168 AD....
—references vary). He classed stellar objects on how bright they appeared — the brightest were "magnitude 1", the next brightest were "magnitude 2", on down to "magnitude 6", the faintest he could see. Thus the scale is roughly 2000 years old.

Absolute scale based on Vega


The star Vega
Vega

Vega is the brightest star in the constellation Lyra, the list of brightest stars in the night sky and the second brightest star in the northern Celestial sphere, after Arcturus....
 is defined to have a magnitude of zero, or at least near. Modern instruments as bolometer
Bolometer

A bolometer is a device for measuring the energy of incident electromagnetic radiation. It was invented in 1878 by the American astronomer Samuel Pierpont Langley....
s and radiometer
Radiometer

A radiometer is a device for measuring the radiometry of electromagnetic radiation. Generally, the term ?radiometer? denotes an infrared radiation detector, yet it also comprises detectors operating on any electromagnetic wavelength, e.g....
s give Vega a brightness of about 0.03. The brightest star, Sirius
Sirius

Sirius is the list of brightest stars in the night sky with a visual apparent magnitude of −1.46, almost twice as bright as Canopus, the next brightest star....
, has a magnitude of -1.46. or -1.5.

Problems


The human eye is easily fooled, and Hipparchus's scale has had problems. For example, the human eye is more sensitive to yellow
Yellow

Yellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, but does not significantly stimulate the S cone cells; that is, light with much red and green but not very much blue....
/ Red
Red

Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625?740 Nanometer....
 light than to blue
Blue

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440?490 Nanometre....
, and photograph
Photograph

A photograph is an created by light falling on a light-sensitive surface, usually photographic film or an electronic imager such as a Charge-coupled device or a Complementary metal?oxide?semiconductor chip....
ic film more to blue than to yellow/red, giving different values of visual magnitude and photographic magnitude
Photographic magnitude

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....
. When we use precise instruments to actually measure light from stars, we find a rough multiplicative
Multiplication

Multiplication is the Operation of scaling one number by another. It is one of the four basic operations in elementary arithmetic .Multiplication is defined for Natural number in terms of repeated addition; for example, 4 multiplied by 3 can be calculated by adding 3 copies of 4 together:...
 factor of 2.5 between (closer 2.512, the 5th root
Nth root

In mathematics, an nth root of a number a is a number b such that when n copies of b are multiplication together, the result is a....
 of 100
100

Year 100 was a leap year starting on Wednesday of the Julian calendar....
), i.e., a magnitude 2 star is roughly 2.5 times less bright than a magnitude 1 star, and so on, thus the scale is logarithmic
Logarithmic

Logarithmic can refer to:* Logarithm-a transcendental function in mathematics* Logarithmic scale-the use of the logarithmic function to describe measurements...
, not linear
Linear

The word linear comes from the Latin word linearis, which means created by lines.In mathematics, a linear map or function f is a function which satisfies the following two properties......
. The use of the 5th root of 100 is difficult in computations as it is an irrational number. Furthermore, many people find it counterintuitive that a high magnitude star is dimmer than a low magnitude star.

The modern world


Astronomer
Astronomer

An astronomer is a scientist who studies Celestial body such as planets, stars, and Galaxy.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws....
s can now measure differences as small as one-hundredth of a magnitude. Stars between magnitudes 1.5 and 2.5 are called second-magnitude; there are 20 stars brighter than 1.5, which are first-magnitude stars.

Apparent and absolute magnitude


Two specific types of magnitudes distinguished by astronomers are:
  • Apparent magnitude
    Apparent magnitude

    The apparent magnitude of a celestial body is a measurement of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the Earth's atmosphere....
    , the apparent brightness of an object. For example, Alpha Centauri
    Alpha Centauri

    Alpha Centauri ; is the brightest star in the southern constellation of Centaurus and an established binary star system, Alpha Centauri AB ....
     has higher apparent magnitude (i.e. lower value) than Betelgeuse
    Betelgeuse

    Betelgeuse is a semiregular variable star located approximately 600 light-years away from Earth. It is the second brightest star in the constellation Orion and the ninth list of brightest stars in the night sky....
    , because it is much closer to the Earth
    Earth

    Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
    .
  • Absolute magnitude
    Absolute magnitude

    In astronomy, absolute magnitude measures a celestial object's intrinsic brightness. To derive the absolute magnitude from the observed apparent magnitude of a celestial object its value is corrected for distance to the observer....
    , which measures the luminosity
    Luminosity

    Luminosity has different meanings in several different fields of science....
     of an object (or reflected light for non-luminous objects like asteroid
    Asteroid

    Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, smaller than planets but larger than meteoroids....
    s); it is the object's apparent magnitude as seen from certain location. For star
    Star

    A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
    s it is 10 parsec
    Parsec

    The parsec is a units of measurement of astronomical units of length, equal to just under 31 orders_of_magnitude_#1012 kilometres , or about 3.26 light-years....
    s (32.6 light years). Betelgeuse has much higher absolute magnitude than Alpha Centauri, because it is much more luminous.
Usually only apparent magnitude is mentioned, because it can be measured directly; absolute magnitude can be derived from apparent magnitude and distance using the distance modulus
Distance modulus

The distance modulus is a way of expressing distances that is often used in astronomy....
.

See also


  • Absolute magnitude
    Absolute magnitude

    In astronomy, absolute magnitude measures a celestial object's intrinsic brightness. To derive the absolute magnitude from the observed apparent magnitude of a celestial object its value is corrected for distance to the observer....
  • Apparent magnitude
    Apparent magnitude

    The apparent magnitude of a celestial body is a measurement of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the Earth's atmosphere....
  • Photographic magnitude
    Photographic magnitude

    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....


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