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Photographic magnitude

 

 
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Photographic magnitude
 
 
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Before the advent of photometer
Photometer

In its widest sense, a photometer is an instrument for measuring Light intensity or optical properties of solutions or surfaces. Photometers are used to measure:...
s which accurately measure the brightness of astronomical objects, the 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....
 of an object was obtained by taking a picture of it with a camera
Camera

A camera is a device that records images, either as a still photograph or as moving images known as videos or movies. The term comes from the camera obscura , an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura....
. These images, made on photoemulsive film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
, were more sensitive to the blue end of the visual spectrum
Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object....
 than the human eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
 or modern photometers. As a result, bluer stars have a lower photographic magnitude than their modern visual magnitude, because they appear brighter on the photograph than they do to modern photometers.






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Encyclopedia


Before the advent of photometer
Photometer

In its widest sense, a photometer is an instrument for measuring Light intensity or optical properties of solutions or surfaces. Photometers are used to measure:...
s which accurately measure the brightness of astronomical objects, the 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....
 of an object was obtained by taking a picture of it with a camera
Camera

A camera is a device that records images, either as a still photograph or as moving images known as videos or movies. The term comes from the camera obscura , an early mechanism of projecting images where an entire room functioned as a real-time imaging system; the modern camera evolved from the camera obscura....
. These images, made on photoemulsive film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
, were more sensitive to the blue end of the visual spectrum
Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object....
 than the human eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
 or modern photometers. As a result, bluer stars have a lower photographic magnitude than their modern visual magnitude, because they appear brighter on the photograph than they do to modern photometers. Conversely, redder stars have a higher photographic magnitude than visual magnitude, because they appear dimmer.

The symbol for photographic magnitude is mpg.

The photographic magnitude scale is now considered obsolete.

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....
  • Magnitude (astronomy)
    Magnitude (astronomy)

    In astronomy, magnitude refers to the logarithmic measure of the brightness of an object, measured in a specific wavelength or passband, usually in light or infrared wavelengths....