आभासी दृश्यप्रत चा उगम बघा

'''आभासी दृश्यप्रत''' (इंग्रजी: Apparent magnitude; चिन्ह '''m''') ही खगोलीय वस्तूची पृथ्वीवरील निरीक्षकाला भासणारी प्रखरता/तेजस्विता दर्शवणारी संख्या आहे. ही संख्या जितकी लहान तितका तारा जास्त तेजस्वी दिसतो. -२७ आभासी दृश्यप्रत असलेला [[सूर्य]] आकाशातील सर्वात तेजस्वी वस्तू आहे. एखादी वस्तू जेवढी जास्त तेजस्वी असते, तिची [[दृश्यप्रत]] तेवढी कमी असते. त्याचबरोबर दृश्यप्रत मापणीची पद्धत [[लॉगॅरिदम|लॉगॅरिदमिक]] असते: म्हणजे दृश्यप्रतीमधील एका एककाचा फरक म्हणजे प्रखरतेमध्ये <math>\sqrt[5]{100}</math> इतक्या म्हणजे २.५१२ पटीचा फरक असतो.

सामान्यत: आभासी दृश्यप्रत सांगण्यासाठी [[दृश्य प्रकाश किरणे|दृश्य वर्णपटाचा]] आधार घेतला जातो. पण काही वेळा इतर वर्णपटही वापरले जातात (उदा. [[अवरक्त किरणे|अवरक्त]]). दृश्य वर्णपटामध्ये 
सूर्यानंतर [[व्याध (तारा)|व्याध]] दुसरा सर्वात तेजस्वी तारा आहे. निकट अवरक्त मधील जे-बॅंडमध्ये काक्षी (भरत) तारा सर्वात तेजस्वी तारा आहे. ताऱ्यांची आभासी दृश्यप्रत [[बोलोमीटर]] या यंत्राने मोजतात.

पुढील तक्त्यामध्ये रात्रीच्या आकाशातील किती आभासी दृश्यप्रतीचे तारे उघड्या डोळ्यांनी दिसू शकतात किंवा नाहीत व त्यांची संख्या दिली आहे.

{|class="wikitable" style=" margin-left: 1em; text-align: center;"
!मानवी डोळ्यांना दिसते<ref name="SIMBAD-mag6.5"/>
!आभासी दृश्यप्रत
![[अभिजित (तारा)|अभिजित]] ताऱ्याच्या तुलनेत तेजस्विता
! रात्रीच्या आकाशात या आभासी <br/> दृश्यप्रतीपेक्षा तेजस्वी दिसणाऱ्या ताऱ्यांची संख्या<ref>{{संकेतस्थळ स्रोत | दुवा = http://www.nso.edu/PR/answerbook/magnitude.html | archiveurl = https://web.archive.org/web/20080206074842/http://www.nso.edu/PR/answerbook/magnitude.html | archivedate = 2008-02-06 | title = मॅग्निट्यूड (Magnitude) | प्रकाशक = National Solar Observatory—Sacramento Peak | accessdate = 2006-08-23 | url-status = dead }}</ref>
|-
|rowspan="9"|होय||−१.०||२५०%||[[व्याध (तारा)|१]]
|-
|०.०||१००%||४
|-
|१.०||४०%||१५
|-
|२.०||१६%||४८
|-
|३.०||६.३%||१७१
|-
|४.०||२.५%||५१३
|-
|५.०||१.०%||१&nbsp;६०२
|-
|६.०||०.४०%||४&nbsp;८००
|-
|६.५||०.२५%||९&nbsp;०९६
|-
| rowspan="4" |नाही||७.०||०.१६%||१४&nbsp;०००
|-
|८.०||०.०६३%||४२&nbsp;०००
|-
|९.०||०.०२५%||१२१&nbsp;०००
|-
|१०.०||०.०१०%||३४०&nbsp;०००
|}

== मोजमाप ==

पृथ्वीच्या वातावरणाचा आभासी तेजस्वितेवर परिणाम होतो. त्यामुळे आभासी दृश्यप्रत मोजताना एखादी खगोलीय वस्तू विना वातावरणाची जेवढी तेजस्वी दिसली असती ती किंमत देतात. प्रखरता अंतरानुसार बदलते. त्यामुळे अतिशय तेजस्वी वस्तू ती खूप लांब असेल तर कमी तेजस्वी दिसू शकते. एखाद्या खगोलीय वस्तूची [[निरपेक्ष दृश्यप्रत]] म्हणजे ती वस्तू १० [[पार्सेक]] किंवा ३२.६ [[प्रकाशवर्ष]] अंतरावर आहे असे गृहीत धरले असतानाची तिची आभासी दृश्यप्रत होय.

''x'' बॅंडमधील आभासी दृश्यप्रत ''m'' पुढील समीकरणाने देतात:

:<math>m_{x} - m_{x,0}= -2.5 \log_{10} \left(\frac {F_x}{F_{x,0} }\right)\,</math>,

जिथे <math>F_x\!\,</math> हा x बॅंडमधील [[अभिवाह]] (फ्लक्स) आहे आणि <math>m_{x,0}</math> व <math>F_{x,0}</math> हे त्याच बॅंडमधील संदर्भासाठीचे आभासी दृश्यप्रत आणि अभिवाह आहेत, जसे की अभिजित ताऱ्याचे.

== उदा: सूर्य आणि चंद्र ==
''सूर्य आणि चंद्राच्या आभासी दृश्यप्रतींचे गुणोत्तर काय आहे?''

सूर्याची आभासी दृश्यप्रत -२६.७४ (तेजस्वी) आहे, तर पौर्णिमेच्या चंद्राची सरासरी आभासी दृश्यप्रत -१२.७४ (कमी तेजस्वी) आहे.

'''दृश्यप्रतेमधील फरकः'''
:<math> x = m_1 - m_2 = (-12.74) - (-26.74) = 14.00 </math>

'''प्रखरतेतील तफावत:'''
:<math> v_b = 10^{0.4 x} = 10^{0.4*14.00} \approx 398400 </math>

सूर्य पौर्णिमेच्या चंद्रापेक्षा ~४०,००० पट जास्त तेजस्वी दिसतो.

== काही खगोलीय वस्तू ==
{| class="wikitable"
|+'''माहीत असलेल्या खगोलीय वस्तूंच्या आभासी दृश्यप्रती'''
|-
! आभासी दृश्यप्रत (V)
! खगोलीय वस्तू
|-
| −40.98 || [[Rho Cassiopeiae]] as seen from 1 [[astronomical unit]] (AU).
|-
| −38.00 || [[Rigel]] as seen from 1 AU. It would be seen as a large very bright bluish scorching ball of 35° apparent diameter.
|-
| −30.30 || [[Sirius]] as seen from 1 astronomical unit
|-
| −29.30 || [[Sun]] as seen from [[Mercury (planet)|Mercury]] at [[perihelion]]
|-
| −27.40 || Sun as seen from [[Venus]] at perihelion
|-
| −26.74<ref name="sun-fact"/> || Sun as seen from [[Earth]] (about 400,000 times brighter than mean full moon)
|-
| −25.60 || Sun as seen from [[Mars]] at [[aphelion]]
|-
| −23.00 || Sun as seen from [[Jupiter]] at aphelion
|-
| −21.70 || Sun as seen from [[Saturn]] at aphelion
|-
| −20.20 || Sun as seen from [[Uranus]] at aphelion
|-
| −19.30 || Sun as seen from [[Neptune]]
|-
| −18.20 || Sun as seen from [[Pluto]] at aphelion
|-
| −16.70 || Sun as seen from [[एरिस (बटु ग्रह)]] at aphelion
|-
| −14.2 || An illumination level of one [[lux]] <ref>[https://books.google.com/books?id=oTraksy4JYkC&pg=PA4 Introduction to Astrophysics: The Stars] – Jean Dufay, page 3</ref><ref name =IM08>Ian S. McLean, ''Electronic imaging in astronomy: detectors and instrumentation'' Springer, 2008, ISBN 3-540-76582-4 page 529</ref>
|-
| −12.90 || Maximum brightness of perigee+perihelion [[full moon]] (mean distance value is −12.74,<ref name="moon-fact"/> though both values are about 0.18 magnitude brighter when including the opposition effect)
|-
| −11.20 || Sun as seen from [[90377 Sedna|Sedna]] at aphelion
|-
| −10 || [[Comet Ikeya–Seki]] (1965), which was the brightest [[Kreutz Sungrazer]] of modern times<ref name="brightest">{{संकेतस्थळ स्रोत |दुवा=http://www.icq.eps.harvard.edu/brightest.html |title=Brightest comets seen since 1935 |publisher=International Comet Quarterly |accessdate=18 December 2011}}</ref>
|-
| −9.50 || Maximum brightness of an [[Iridium flare|Iridium (satellite) flare]]
|-
| −7.50 || The [[SN 1006]] supernova of AD 1006, the brightest stellar event in recorded history (7200 light years away)<ref name="SN1006"/>
|-
| −6.50 || The total [[integrated magnitude]] of the [[night sky]] as seen from [[Earth]]
|-
| −6.00 || The Crab Supernova ([[SN 1054]]) of AD 1054 (6500 light years away)<ref name=SN1054/>
|-
| −5.9  || [[International Space Station]] (when the ISS is at its [[perigee]] and fully lit by the Sun)<ref>{{संकेतस्थळ स्रोत
| दुवा = http://www.heavens-above.com/satinfo.aspx?SatID=25544
| title = ISS Information - Heavens-above.com
| publisher = Heavens-above
| accessdate = 2007-12-22}}</ref>
|-
| −4.89
| Maximum brightness of [[Venus]]<ref name="Horizons-Venus"/> when illuminated as a crescent
|-
| −4.00
| Faintest objects observable during the day with naked eye when Sun is high
|-
| −3.99
| Maximum brightness of [[Epsilon Canis Majoris]] 4.7 million years ago, the historical [[List of brightest stars|brightest star]] of the [[Historical brightest stars|last and next five million years]]
|-
| −3.82
| Minimum brightness of [[Venus]] when it is on the far side of the Sun
|-
| −2.95
| Maximum brightness of [[Mars]]<ref name="mars"/>
|-
| −2.70
| Maximum brightness of [[Jupiter]]<ref name="jupiter"/>
|-
| −2.50
| Faintest objects visible during the day with naked eye when Sun is less than 10° above the horizon
|-
| −2.50
| Minimum brightness of [[new moon]] 
|-
| −2.45
| Maximum brightness of [[Mercury (planet)|Mercury]] at [[superior conjunction]] (unlike Venus, Mercury is at its brightest when on the far side of the Sun, the reason being their different [[phase curve (astronomy)|phase curve]]s)
|-
| −1.61
| Minimum brightness of [[Jupiter]]
|-
| −1.47 || Brightest star (except for the Sun) at visible wavelengths: [[Sirius]]<ref name="SIMBAD-Sirius"/>
|-
| −0.83 || [[Eta Carinae]] apparent brightness as a [[supernova impostor]] in April 1843
|-
| −0.72 || Second-brightest star: [[Canopus (star)|Canopus]]<ref name="SIMBAD-Canopus"/>
|-
| −0.49
| Maximum brightness of [[Saturn]] at opposition and perihelion when the rings are full open (2003)
|-
| −0.27
| The total magnitude for the [[Alpha Centauri|Alpha Centauri AB]] star system. (Third-brightest star to the naked eye)
|-
| −0.04 || Fourth-brightest star to the naked eye [[Arcturus (star)|Arcturus]]<ref name="SIMBAD-Arcturus"/>
|-
| −0.01 || Fourth-brightest ''individual'' star visible telescopically in the sky [[Alpha Centauri|Alpha Centauri A]]
|-
| +0.03
| [[Vega]], which was originally chosen as a definition of the zero point<ref name="SIMBAD-Vega"/>
|-
| +0.50 || [[Sun]] as seen from [[Alpha Centauri]]
|-
| 1.47
| Minimum brightness of [[Saturn]]
|-
| 1.84
| Minimum brightness of [[Mars]]
|-
| 3.03
| The [[SN 1987A]] supernova in the [[Large Magellanic Cloud]] 160,000 light-years away.
|-
| 3 to 4
| Faintest stars visible in an urban neighborhood with naked eye
|-
| 3.44
| The well known [[Andromeda Galaxy]] (M31)<ref name="SIMBAD-M31"/>
|-
| 4.38
| Maximum brightness of [[Ganymede (moon)|Ganymede]]<ref name=horizons-Ganymede/> (moon of Jupiter and the largest moon in the Solar System)
|-
| 4.50
| [[Messier 41|M41]], an open cluster that may have been seen by [[Aristotle]]<ref name="Aristotle">{{संकेतस्थळ स्रोत
  |date=2006-07-28
  |title=M41 possibly recorded by Aristotle
  |publisher=SEDS (Students for the Exploration and Development of Space)
  |दुवा=http://messier.seds.org/more/m041_ari.html
  |accessdate=2009-11-29}}</ref>
|-
| 5.20
| Maximum brightness of asteroid [[4 Vesta|Vesta]]
|-
| 5.32
| Maximum brightness of [[Uranus]]<ref name="uranus"/>
|-
| 5.72
| The spiral galaxy [[Triangulum Galaxy|M33]], which is used as a test for [[naked eye]] seeing under dark skies<ref name="SIMBAD-M33">{{संकेतस्थळ स्रोत
 |title=SIMBAD-M33
 |publisher=SIMBAD Astronomical Database
 |दुवा=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=M33
 |accessdate=2009-11-28}}</ref><ref name="M33">{{संकेतस्थळ स्रोत
  |date=1993
  |title=M33 (Triangulum Galaxy)
  |first=Jerry
  |last=Lodriguss
  |दुवा=http://www.astropix.com/HTML/A_FALL/M33.HTM
  |accessdate=2009-11-27}} (shows b mag not v mag)</ref>
|-
| 5.73
| Minimum brightness of [[Mercury (planet)|Mercury]]
|-
| 5.8
| Peak visual magnitude of [[gamma-ray burst]] [[GRB 080319B]] (the "Clarke Event") seen on Earth on March 19, 2008 from a distance of 7.5 billion light-years.
|-
| 5.95
| Minimum brightness of [[Uranus]]
|-
| 6.49
| Maximum brightness of asteroid [[2 Pallas|Pallas]]
|-
| 6.50
| Approximate limit of [[star]]s observed by a '''mean''' [[naked eye]] observer under very good conditions. There are about 9,500 stars visible to mag 6.5.<ref name="SIMBAD-mag6.5"/>
|-
| 6.64
| Maximum brightness of dwarf planet [[Ceres (dwarf planet)|Ceres]] in the asteroid belt
|-
| 6.75
| Maximum brightness of asteroid [[7 Iris|Iris]]
|-
| 6.90
| The spiral galaxy [[Messier 81|M81]] is an extreme [[naked eye|naked-eye]] target that pushes human eyesight and the [[Bortle scale]] to the limit<ref name="SEDS">{{संकेतस्थळ स्रोत
  |date=2007-09-02
  |title=Messier 81
  |publisher=SEDS (Students for the Exploration and Development of Space)
  |दुवा=http://messier.seds.org/m/m081.html
  |accessdate=2009-11-28}}</ref>
|-
| 7 to 8
| Extreme naked-eye limit, Class 1 on [[Bortle scale]], the darkest skies available on Earth<ref name="Bortle">{{संकेतस्थळ स्रोत |date = February 2001|title=The Bortle Dark-Sky Scale |publisher=Sky & Telescope |author=John E. Bortle |दुवा=http://www.skyandtelescope.com/resources/darksky/3304011.html |accessdate=2009-11-18}}</ref>
|-
| 7.78
| Maximum brightness of [[Neptune]]<ref name="neptune"/>
|-
| 8.02
| Minimum brightness of Neptune
|-
| 8.10
| Maximum brightness of [[Titan (moon)|Titan]] (largest moon of Saturn),<ref name=horizons-Titan/><ref name=arval/> mean opposition magnitude 8.4<ref name=jpl-sat/>
|-
| 8.94
| Maximum brightness of asteroid [[10 Hygiea]]<ref name=AstDys-Hygiea/>
|-
| 9.50
| Faintest objects visible using common 7x50 [[binoculars]] under typical conditions<ref name="binoculars"/>
|-
| 10.20
| Maximum brightness of [[Iapetus (moon)|Iapetus]]<ref name=arval/> (brightest when west of Saturn and takes 40 days to switch sides)
|-
| 12.91 || Brightest [[quasar]] [[3C 273]] ([[luminosity distance]] of 2.4 billion [[light year]]s)
|-
| 13.42
| Maximum brightness of [[Triton (moon)|Triton]]<ref name=jpl-sat/>
|-
| 13.65
| Maximum brightness of [[Pluto#Physical characteristics|Pluto]]<ref name="pluto"/> (725 times fainter than magnitude 6.5 naked eye skies)
|-
| 15.40
| Maximum brightness of [[Centaur (minor planet)|centaur]] [[2060 Chiron|Chiron]]<ref name=AstDys-Chiron/>
|-
| 15.55
| Maximum brightness of [[Charon (moon)|Charon]] (the large moon of Pluto)
|-
| 16.80
| Current [[Opposition (astronomy and astrology)|opposition]] brightness of [[Makemake]]<ref name=AstDys-Makemake/>
|-
| 17.27
| Current opposition brightness of [[Haumea]]<ref name=AstDys-Haumea/>
|-
| 18.70
| Current opposition brightness of [[एरिस (बटु ग्रह)|एरिस]]
|-
| 20.70
| [[Callirrhoe (moon)|Callirrhoe]] (small ~8&nbsp;km satellite of Jupiter)<ref name=jpl-sat/>
|-
| 22.00
| Approximate limiting magnitude of a 24" [[Ritchey-Chrétien telescope]] with 30 minutes of stacked images (6 subframes at 300s each) using a [[Charge-coupled device|CCD detector]]<ref name="24inch">{{संकेतस्थळ स्रोत
  |date=2009-10-05
  |title=17 New Asteroids Found by LightBuckets
  |publisher=LightBuckets
  |author=Steve Cullen (sgcullen)
  |दुवा=http://www.lightbuckets.com/news/37/17-new-asteroids-found-by-lightbuckets/
  |accessdate=2009-11-15}}</ref>
|-
| 22.91
| Maximum brightness of Pluto's moon [[Hydra (moon)|Hydra]]
|-
| 23.38
| Maximum brightness of Pluto's moon [[Nix (moon)|Nix]]
|-
| 24.80
| Amateur picture with greatest magnitude: quasar CFHQS J1641 +3755<ref>Cooperation with Ken Crawford</ref><ref name="CFHQS_J1641_f10">{{संकेतस्थळ स्रोत |title=CRedshift 6 Quasar (CFHQS J1641 +3755)  |दुवा=http://panther-observatory.com/gallery/deepsky/doc/CFHQS_J1641_f10.htm}}</ref> and limit of a 30-second exposure with [[Large Synoptic Survey Telescope]] (LSST).
|-
| 25.00
| [[Fenrir (moon)|Fenrir]] (small ~4&nbsp;km satellite of Saturn)<ref name=sheppard-saturn/>
|-
| 27.70
| Faintest objects observable in a 10-hour image with a 8-meter class ground-based telescope such as the [[Subaru Telescope]]<ref>[http://www.skyandtelescope.com/astronomy-resources/astronomy-questions-answers/what-is-the-faintest-object-imaged-by-ground-based-telescopes/ What is the faintest object imaged by ground-based telescopes?], by: The Editors of Sky Telescope, July 24, 2006</ref>
|-
| 28.00
| Jupiter if it were located 5000 [[astronomical unit|au]] from the Sun<ref>Magnitude difference is 2.512*log<sub>10</sub>[(5000/5)^2 X (4999/4)^2] ≈ 30.6, so Jupiter is 30.6 mag fainter at 5000 au</ref>
|-
| 28.20
| [[Halley's Comet]] in 2003 when it was 28 au from the Sun<ref name="ESO2003">{{संकेतस्थळ स्रोत |title=New Image of Comet Halley in the Cold  |दुवा=http://www.eso.org/public/outreach/press-rel/pr-2003/phot-27-03.html |publisher=[[ESO]] |date=2003-09-01 |accessdate=2009-02-22| archiveurl= https://web.archive.org/web/20090301212846/http://www.eso.org/public/outreach/press-rel/pr-2003/phot-27-03.html| archivedate= 1 March 2009 <!--DASHBot-->| मृतदुवा= no}}</ref>
|-
| 31.50
| Faintest objects observable in visible light with [[Hubble Space Telescope]]<ref>[http://arxiv.org/abs/1305.1931 The HST eXtreme Deep Field XDF: Combining all ACS and WFC3/IR Data on the HUDF Region into the Deepest Field Ever]</ref>
|-
| 35.00
| [[LBV 1806-20]], a luminous blue variable star, expected magnitude at visible wavelengths due to [[interstellar extinction]]
|-
| 36.00
| Faintest objects observable in visible light{{citation needed|date=October 2012}} with [[European Extremely Large Telescope|E-ELT]]
|-
| colspan=2|{{See also|List of brightest stars}}
|}

== संदर्भ ==
{{संदर्भयादी|2}}

[[वर्ग:खगोलशास्त्र]]