Magnitudes Definition and 110 Threads

Apparent magnitude (m) is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer.
The word magnitude in astronomy, unless stated otherwise, usually refers to a celestial object's apparent magnitude. The magnitude scale dates back to the ancient astronomer Ptolemy, whose star catalog listed stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined in a way to closely match this historical system.
The scale is reverse logarithmic: the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to a brightness ratio of 5√100, or about 2.512. For example, a star of magnitude 2.0 is 2.512 times brighter than a star of magnitude 3.0, 6.31 times brighter than a star of magnitude 4.0, and 100 times brighter than one of magnitude 7.0.
The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46. The faintest stars visible with the naked eye on the darkest night have apparent magnitudes of about +6.5, though this varies depending on a person's eyesight and with altitude and atmospheric conditions. The apparent magnitudes of known objects range from the Sun at −26.7 to objects in deep Hubble Space Telescope images of magnitude +31.5.The measurement of apparent magnitude is called photometry. Photometric measurements are made in the ultraviolet, visible, or infrared wavelength bands using standard passband filters belonging to photometric systems such as the UBV system or the Strömgren uvbyβ system.
Absolute magnitude is a measure of the intrinsic luminosity of a celestial object rather than its apparent brightness and is expressed on the same reverse logarithmic scale. Absolute magnitude is defined as the apparent magnitude that a star or object would have if it were observed from a distance of 10 parsecs (3.1×1014 kilometres). When referring to just "magnitude", apparent magnitude rather than absolute magnitude is normally intended.

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  1. Jd1431

    I How Can Measured Satellite Magnitudes Be Converted to Radiant Intensity?

    I have the measured magnitudes of a satellite object in four filters and I want to convert this into into Radiant Intensity. I was told that if I integrated the solar spectrum over my filter bandpasses , I could obtain the visual mag of the sun in each of these filters and use this to obtain the...
  2. WMDhamnekar

    MHB Velocity and acceleration vectors and their magnitudes

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  3. K

    B Magnitudes of the sum of two vectors

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  4. H

    The magnitudes of the applied force F and the frictional force f of a wheel

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  5. G

    How to calculate the magnitudes of three forces around a hexagon

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  6. T

    B Why is an inverse logarithmic scale chosen for the magnitudes of stars?

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  7. T

    What are the uncertainty values for my corrected magnitudes?

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  8. StillLearningToronto

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  9. A

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  10. T

    Combined magnitudes of two solar-type stars

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  11. Callum Plunkett

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  12. C

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  13. G

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  14. C

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  15. DevonZA

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  16. Rodriesk

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  17. TheSodesa

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  18. G

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    I've taken up to Calc. III (vector/multi-variable calculus) but have not had any classes that used intensive calculus for a few semesters. However, I'm now in a quantum physics class (its a glorified title really--it's more or less "modern physics") and am looking to see if I am correct in my...
  19. samjohnny

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  20. S

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  21. C

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  22. P

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  23. G

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  24. Kerrigoth

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  25. S

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  26. N

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  27. S

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  28. entropy1

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  29. L

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  30. T

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  31. K

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  32. O

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  33. Maxo

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  34. G

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  35. B

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  36. N

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  37. D

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  38. N

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  39. N

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  40. D

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  41. N

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  42. W

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  43. A

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  44. S

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  45. N

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  46. A

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  47. S

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  48. S

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  49. C

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  50. W

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