Editing Apparent magnitude (section)

== Standard reference values ==
{| class="wikitable floatright" style="text-align:center;"
|+ Standard apparent magnitudes and fluxes for typical bands<ref name="UTmags">{{cite web
 |title=Astronomical Magnitude Systems
 |publisher=Harvard-Smithsonian Center for Astrophysics
 |first=John
 |last=Huchra
 |url=https://www.cfa.harvard.edu/~dfabricant/huchra/ay145/mags.html
 |access-date=18 July 2017
 |archive-url=https://web.archive.org/web/20180721162252/https://www.cfa.harvard.edu/~dfabricant/huchra/ay145/mags.html
 |archive-date=21 July 2018
 |url-status=live
 }}</ref>
|-
! rowspan="2" | Band
! rowspan="2" | {{mvar|λ}}<br />(μm)
! rowspan="2" | {{math|{{sfrac|Δ''λ''|''λ''}}}}<br />([[full width at half maximum|FWHM]])
! colspan="2" | Flux at {{math|''m'' {{=}} 0}}, {{math|''F''<sub>''x'',0</sub>}}

|-
! [[Jansky|Jy]]
! 10<sup>−20</sup>&nbsp;erg/(s·cm<sup>2</sup>·Hz)
|-
| U || 0.36 || 0.15 || 1810 || 1.81
|-
| B || 0.44 || 0.22 || 4260 || 4.26
|-
| V || 0.55 || 0.16 || 3640 || 3.64
|-
| R || 0.64 || 0.23 || 3080 || 3.08
|-
| I || 0.79 || 0.19 || 2550 || 2.55
|-
| J || 1.26 || 0.16 || 1600 || 1.60
|-
| H || 1.60 || 0.23 || 1080 || 1.08
|-
| K || 2.22 || 0.23 || {{0}}670 || 0.67
|-
| L || 3.50 || || ||
|-
| g || 0.52 || 0.14 || 3730 || 3.73
|-
| r || 0.67 || 0.14 || 4490 || 4.49
|-
| i || 0.79 || 0.16 || 4760 || 4.76
|-
| z || 0.91 || 0.13 || 4810 || 4.81
|-
|}

The magnitude scale is a reverse logarithmic scale.  A common misconception is that the logarithmic nature of the scale is because 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]] {{xref|(see [[Stevens' power law]])}}.<ref>{{cite journal|title=Misconceptions About Astronomical Magnitudes|author-link=Eric Schulman|first1=E.|last1=Schulman|first2=C. V.|last2=Cox|journal=American Journal of Physics|volume=65|issue=10|page=1003|date=1997|bibcode = 1997AmJPh..65.1003S |doi = 10.1119/1.18714 }}</ref>

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 it varies depends on the type of light detector. For this reason, it is necessary to specify how the magnitude is measured 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&nbsp;nm, in the near [[ultraviolet]]), B (about 435&nbsp;nm, in the blue region) and V (about 555&nbsp;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 human eye. When an apparent magnitude is discussed without further qualification, the V magnitude is generally understood.<ref>{{Cite web |title=Magnitude {{!}} Brightness, Apparent Magnitude & Absolute Magnitude {{!}} Britannica |url=https://www.britannica.com/science/magnitude-astronomy |access-date=2023-10-19 |website=www.britannica.com |language=en}}</ref>

Because cooler stars, such as [[red giant]]s and [[red dwarf]]s, emit little energy in the blue and UV regions of the spectrum, their power is often under-represented by the UBV scale. Indeed, some [[stellar classification|L and T class]] stars have an estimated magnitude of well over 100, because they emit extremely little visible light, but are strongest in [[infrared]].<ref>{{Cite web |title=Introduction to active galaxies: View as single page |url=https://www.open.edu/openlearn/science-maths-technology/introduction-active-galaxies/content-section-5.4/?printable=1 |access-date=2023-10-19 |website=www.open.edu}}</ref>

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 human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light. Magnitudes obtained from this method are known as [[photographic magnitude]]s, and are now considered obsolete.<ref>{{Cite journal |title=1910HarCi.160....1P Page 1 |url=https://adsabs.harvard.edu/full/1910HarCi.160....1P |access-date=2023-10-19 |journal=Harvard College Observatory Circular|bibcode=1910HarCi.160....1P |last1=Pickering |first1=Edward C. |date=1910 |volume=160 |page=1 }}</ref>

For objects within the [[Milky Way]] with a given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object. For objects at very great distances (far beyond the Milky Way), this relationship must be [[K correction|adjusted for redshifts]] and for [[Non-Euclidean geometry|non-Euclidean]] distance measures due to [[general relativity]].<ref name=umeh>{{cite journal|bibcode=2014CQGra..31t5001U|arxiv=1402.1933|title=Nonlinear relativistic corrections to cosmological distances, redshift and gravitational lensing magnification: II. Derivation|journal=Classical and Quantum Gravity|volume=31|issue=20|page=205001|last1=Umeh|first1=Obinna|last2=Clarkson|first2=Chris|last3=Maartens|first3=Roy|year=2014|doi=10.1088/0264-9381/31/20/205001|s2cid=54527784}}</ref><ref name=hogg>{{cite arXiv|eprint=astro-ph/0210394|title=The K correction|last1=Hogg|first1=David W.|last2=Baldry|first2=Ivan K.|last3=Blanton|first3=Michael R.|last4=Eisenstein|first4=Daniel J.|year=2002}}</ref>

For planets and other Solar System bodies, the apparent magnitude is derived from its [[Phase curve (astronomy)|phase curve]] and the distances to the Sun and observer.<ref>{{Cite journal |title=1967lts..conf..205W Page 205 |url=https://adsabs.harvard.edu/full/1967lts..conf..205W |access-date=2023-10-19 |journal=Late-Type Stars|bibcode=1967lts..conf..205W |last1=Wing |first1=R. F. |date=1967 |page=205 }}</ref>

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