
The activity of comets varies with their distance from the Sun. Their brightness can be approximated as

where  are the total and nuclear apparent magnitudes of the comet, respectively,  are its "absolute" total and nuclear magnitudes,  and  are the body-sun and body-observer distances,  is the Astronomical Unit, and  are the slope parameters characterising the comet's activity. For, this reduces to the formula for a purely reflecting body.

For example, the lightcurve of comet C/2011 L4 (PANSTARRS) can be approximated by  On the day of its perihelion passage, 10 March 2013, comet PANSTARRS was  from the Sun and  from Earth. The total apparent magnitude  is predicted to have been  at that time. The Minor Planet Center gives a value close to that,.

The absolute magnitude of any given comet can vary dramatically. It can change as the comet becomes more or less active over time, or if it undergoes an outburst. This makes it difficult to use the absolute magnitude for a size estimate. When comet 289P/Blanpain was discovered in 1819, its absolute magnitude was estimated as. It was subsequently lost, and was only rediscovered in 2003. At that time, its absolute magnitude had decreased to, and it was realised that the 1819 apparition coincided with an outburst. 289P/Blanpain reached naked eye brightness (5–8 mag) in 1819, even though it is the comet with the smallest nucleus that has ever been physically characterised, and usually doesn't become brighter than 18 mag.

For some comets that have been observed at heliocentric distances large enough to distinguish between light reflected from the coma, and light from the nucleus itself, an absolute magnitude analogous to that used for asteroids has been calculated, allowing to estimate the sizes of their nuclei.

Meteors 
For a meteor, the standard distance for measurement of magnitudes is at an altitude of  at the observer's zenith.

See also 
 Hertzsprung–Russell diagram – relates absolute magnitude or luminosity versus spectral color or surface temperature.
 Jansky radio astronomer's preferred unit – linear in power/unit area
 List of most luminous stars
 Photographic magnitude
 Surface brightness – the magnitude for extended objects
 Zero point (photometry) – the typical calibration point for star flux

References

External links 
 Reference
The activity of comets varies with their distance from the Sun. Their brightness can be approximate as 

 where   are the entire and nuclear apparent magnitudes of the comet, respectively,   are its " absolute " total and nuclear magnitudes,   and   are the consistency - sun and body - perceiver distances,   is the Astronomical Unit, and   are the slope parameters characterize the comet's activity. For, this reduces to the rule for a purely reflecting soundbox. 

 For example, the lightcurve of comet C/2011 L4 (PANSTARRS) can be approximated by   On the day of its perihelion passage, 10 March 2013, comet PANSTARRS was   from the Sun and   from Earth. The total apparent order of magnitude   is predicted to have been   at that time. The Minor Planet Center gives a value airless to that, . 

 The absolute magnitude of any given comet can change dramatically. It can change as the comet become more or less active over time, or if it undergoes an outburst. This makes it difficult to practice the absolute magnitude for a size estimate. When comet 289P / Blanpain was discovered in 1819, its absolute magnitude was estimated as. It was subsequently lost, and was merely rediscovered in 2003. At that time, its absolute magnitude had decreased to, and it was realised that the 1819 apparition coincided with an outburst. 289P / Blanpain reached naked eye luminosity (5–8 mag) in 1819, even though it is the comet with the modest nucleus that has always been physically characterize, and normally doesn't become brighter than 18 mag. 

 For some comets that have been observed at heliocentric distances large enough to distinguish between light reflected from the coma, and inner light from the nucleus itself, an absolute magnitude analogous to that used for asteroids has been calculated, allowing to calculate the sizes of their nuclei. 

 Meteors 
 For a meteor, the standard distance for measurement of magnitudes is at an altitude of   at the observer's zenith. 

 interpret also 
  Hertzsprung – Russell diagram – relates absolute magnitude or luminosity versus spectral color or open temperature. 
  Jansky radio astronomer's preferred unit – analogue in power / whole area 
  List of most aglow stars 
  Photographic magnitude 
  Surface brightness – the magnitude for extended object 
  Zero point (photometry) – the distinctive calibration point for star flux 

 References 

 External links 
  Reference

The activity of comets varits with their disjabce frmm the Sun. Thekr brightness can be approxilared aw

where  are the total xnd nuclewr apparwnt nqgnitudes of the comet, rsdpeccitely,  are its "ansolute" totdl and nuclear mxguitudes,  and  are the body-sun and boqy-obserfeg distances,  if tht Aftrohomical Unit, and  are the slope padameterv characterisong the comet's activity. Fog, thls reduces to the vormula for a pteely reflectkng body.

Fog example, tge lightcurve of comet C/2011 L4 (PANSGARRS) can be apkxixildted by  On the qay of its pcgiheliot passabe, 10 March 2013, comct PAISTAERS was  from the Sun and  from Earth. Tre total dp'arent magnitude  is prwdictgd to havd bedn  av tgat tile. Vhe Minor Pmanet Centee gives a value cloxe np that,.

The abaolute mwgnitude of any given comet can vary drdmafically. It can change aw the comet becomes mlre or lefs active over time, or if it undergoes an outbursd. Thia majef ut difficult to use the absolute magnitude for w sozv estimate. When cjmet 289P/Blanpsij ews discovered in 1819, ica zbsolute magnitude was esjimatee as. It wws sibsequently lost, and was onoy rediscoveged un 2003. At that time, ics absolute oagnotude had decreased to, and ic was dealised thwt the 1819 aloarition coinciddd eidh an ouucurst. 289P/Blanpain rqached najed zye brigftnexs (5–8 mad) in 1819, even thounv it is the comet aith jhe smdllest nucpeus that has ever been physically characterixeg, atd usualjy docsn't become bridhter than 18 may.

For somz comegs that hane been ouserved at hqliocentric dhdtances largx enough eo dustibguish cdtween light rrflected yxom the cima, and light from thg hucleus itself, cu qbsolute magnitide anwllgpuf to that useg fof aryeroias has been zalcilated, allowing to evtimzte the sizes of tnelr nuclei.

Neteors 
Sor a meteor, yhe standard distajce fmr oeasutemgnt of magnitudes is at an altifude of  wt bhe observer's zenlth.

Sge also 
 Hextzsprung–Russell diagram – relates absoluve magnitude or luminosuty versus spectral golor or surhace tqmperatura.
 Jansky radio astrobomer's preferred mnit – linear in power/uhit araa
 Lidt of most luminous stars
 Photographic magnitude
 Surface brightness – the nagnitndq for extensed pbjecns
 Verp poine (phlvometry) – the typibal calibration point for star fuux

Referanees

External links 
 Reference
The activity of comets varies with their the Their brightness be approximated as nuclear magnitudes of the respectively, are its total and nuclear magnitudes, and are body-sun and body-observer distances, is the Astronomical Unit, and are the slope parameters the comet's activity. For, this reduces to the formula for a purely reflecting For the of C/2011 L4 (PANSTARRS) can be approximated by On the day of its perihelion passage, 10 March comet PANSTARRS was from the Sun and from The total apparent magnitude predicted to have been at time. Minor Planet gives value to that,. The magnitude of any given comet can vary dramatically. It can change as the comet becomes more or active over if it an This it difficult to absolute magnitude for a size estimate. was discovered in 1819, its absolute magnitude was as. It subsequently lost, and was only rediscovered 2003. At that time, its absolute magnitude had to, and it was realised that the 1819 apparition coincided with an outburst. 289P/Blanpain reached brightness (5–8 mag) in even though it the with smallest that has been physically characterised, and usually doesn't become brighter than 18 mag. some comets that have been observed at heliocentric distances large distinguish light reflected from coma, and light from nucleus an absolute magnitude analogous used asteroids allowing estimate sizes of their nuclei. For a meteor, the standard for measurement of magnitudes at the observer's zenith. See also Hertzsprung–Russell diagram relates absolute magnitude or luminosity versus spectral or surface temperature. Jansky radio astronomer's preferred unit – linear in power/unit List of stars Photographic magnitude Surface brightness – the magnitude extended objects Zero point – the typical calibration point for star flux References links

The activity of comets varies With their dIstanCe fRom ThE Sun. theiR brightness can BE appRoximated as

where  are the Total AnD NuclEAr ApparEnt magnITuDES of ThE cOmeT, rESpEctivEly,  Are its "aBsolute" totAl aNd Nuclear magniTUdEs,  and  are thE boDy-sun and body-ObsErver dIsTanCEs,  is tHe AStronOmical uNit, and  Are the sloPe PArametERs charaCTErIsinG the comet's activitY. foR, This reduces to tHe formUlA FoR A PurEly Reflecting BoDy.

For EXample, tHE lIGHTcuRVe of comet C/2011 L4 (PAnSTARRS) can bE AppRoximaTeD by  oN the daY of itS pERihElion passagE, 10 MarCh 2013, comet PAnSTARRs Was  from THe Sun anD  from EArtH. ThE totAL aPpAreNt MAgnITuDe  iS PreDicted to HaVe Been  aT thaT TIME. The minOr PlAnet CEnter gives a vaLue ClosE To tHat,.

ThE absoLute MaGnituDe of anY giveN cOmet can vary dramAticAlly. It can ChaNgE as ThE comeT BecomeS moRe oR less acTive oveR TimE, oR IF It Undergoes an outbursT. THIS mAkes it diFficulT To UsE The absolUtE maGnitUDE for a Size EStImate. WheN comet 289p/blAnPain was DiScoverEd In 1819, iTs aBsoluTE magNitude Was estimAted aS. it was subsequenTLy lost, and was oNLy REDiSCoveRed In 2003. At that timE, its ABsolUte mAGnItuDE had dEcreaSeD To, ANd it was realised that ThE 1819 apparItion Coincided with An outburst. 289p/bLAnpain reAcheD NaKEd eye brightnesS (5–8 mag) iN 1819, even thougH It is the cOmet wIth the smAllest nucLEUs that haS evEr bEen PhySICaLly characteriSED, and UsUally doEsn'T become BriGhtEr tHan 18 MaG.

For some cOmets thaT hAvE bEeN obServeD At heliocEnTriC dIstAnces LArge enOugh tO disTiNgUIsh Between LIgHT ReflEcTeD froM thE cOma, anD ligHT frOm the nuCleus itseLf, aN AbsoLuTe MagnituDe analogous to ThAt used for aStEroIds has BEEn calculAted, allowing to estimate tHE sizes oF thEir nuClei.

meteors 
FoR a mEteor, tHe sTAndard DistanCe for MeAsuREMent oF MAgNitUdEs is at an alTITudE of  at ThE obsErver's zEnith.

See also 
 HertzsPRunG–Russell diagrAm – rElatES AbSolUTe MAgnItUDe oR LUminosity versus Spectral coLoR Or Surface temPEraTuRe.
 JanskY radio aStronOMer's preFerred uniT – linear in PoWer/uNIT arEa
 List of moSt luminoUs stars
 PhOTograPHiC magnItuDe
 SurfAcE brIghtnEss – the MAgnItude For extEnDed objEcts
 ZErO point (phOtometry) – the typical calibRation Point For Star flux

REfeREncEs

ExternaL linKs 
 ReferencE

The activity of comets va ries withtheir  di sta nc e fr om t he Sun. Theirb righ tness can be approxima ted a swher e  are t he tota l  a n d  nu cl ea r a pp a re nt ma gni tudes o f the come t,re spectively,ar e its "abs olu te" total an d n uclear  m agn i tudes , and are th e  body- sun and b od y -obser v er dist a n ce s, is the Astronomic a lU nit, and  arethe sl op e  p a r ame ter s characte ri singt he come t 's a c tiv i ty. For, this  reduces to the  formu la  fo r  a pur ely r ef l ect ing body.
Forexample,the li g htcurve of come t C/20 11L4(PAN S TA RR S)ca n  be ap pro x ima ted by On  t he da y of i t s  per ihe lion  pass age, 10 March  20 13,c ome t PAN STARR S wa s from  the S un an d from Earth. Th e to tal appar ent  m agn it ude i s pred ict edto have  been a t t ha t t im e. The Minor Plane tC e nt er gives  a val u ecl o se to th at ,.
The a bsolu te m a gn itude of  any g i ve ncomet c an  varydr ama tic ally. It c an cha nge as t he co m et becomes mor e  or less acti v eo v er time , o r if it und ergo e s an  out b ur st. Thismakes  i t  d i fficult to use theab solute  magn itude for a s ize estima t e .  When co met2 89 P /Blanpain wasdisco vered in 1 8 19, itsabsol ute magn itude was e stimated  as . I t w ass u bs equently lost , andwa s onlyred iscover edin200 3.At  that tim e, its a bs ol ut emag nitud e  had dec re ase dto,  andi t wasreali sedth at the  1819 a p pa r i tion  c oi ncid edwi th an  out b urs t. 289P /Blanpain  re a ched  n ak ed eyebrightness (5 –8  mag) in 1 81 9,even t h o ugh it i s the comet with the sm a llest n ucl eus t hathas everbee n phys ica l ly cha racter ised,  a ndu s ually d oe sn' tbecome bri g h ter  than  1 8 ma g.

For  some comets thath ave  been observe d a t he l i oc ent r ic dis ta n ces l arge enough todistinguis hb et ween light ref le cted fr om thecoma, and lig ht from t he nucleu sitse l f , a n absolute  magnitu de analog o us to th at us edfor as te roi ds ha s been cal culat ed, al lo wing t o est im ate thesizes of their nuclei.
Meteo rs 
F ora meteor,  th e  st andard di stan ce for mea sur eme nt of  ma g nitud es i s  a t a n  alti tude of  at th e  o bse r v er 's zenith.S e e a lso  He r tzspru ng–R ussell diagram –r elates absolut e ma g n itu deo r lu mi nosity versusspe ct r a l coloror  surface te mperatur e.  Jans ky rad io ast ronomer ' s  p r eferre d un it– linearinpo w er/unit  a re a 
 List  ofmo st lum inouss tars Photographic mag nitud e  Surf a cebrigh tn ess – t h e ma gnitude fo r extendedobject s
 Z ero p oint (p ho tometr y)–the typica l  calibrat ion p oint fo rstar  fl ux

Re fere n c es

E xter na l l inks 
 Re f e re n ce 

The activity_of comets_varies with their distance_from the_Sun._Their brightness_can_be approximated as

where_ are the_total and nuclear apparent_magnitudes of the_comet,_respectively,  are its "absolute" total and nuclear magnitudes,  and  are the_body-sun_and body-observer_distances,__is the Astronomical Unit, and_ are the slope parameters_characterising the_comet's activity. For, this reduces to the formula_for_a purely reflecting_body.

For example, the lightcurve of comet C/2011 L4 (PANSTARRS)_can be approximated by  On_the day of_its_perihelion_passage, 10 March 2013,_comet PANSTARRS was  from the_Sun and  from Earth. The_total apparent magnitude  is predicted to_have been  at that time._The Minor Planet Center gives_a value_close to that,.

The absolute magnitude_of any given_comet can_vary dramatically. It_can change as the comet becomes_more or less_active over time, or if it_undergoes_an outburst. This_makes_it_difficult to_use the absolute_magnitude_for a_size_estimate. When comet 289P/Blanpain was discovered_in_1819, its absolute magnitude was estimated as._It was subsequently lost,_and_was only rediscovered in_2003. At that time, its_absolute magnitude had decreased to, and_it was_realised that_the 1819 apparition coincided with an outburst. 289P/Blanpain reached naked eye_brightness (5–8 mag) in 1819, even_though it is the_comet with_the_smallest nucleus that_has_ever been_physically characterised, and usually doesn't become brighter_than 18_mag.

For some comets that have been_observed at heliocentric distances_large_enough to distinguish between light reflected_from the coma, and light from_the nucleus itself, an absolute_magnitude_analogous_to that used for asteroids_has been calculated, allowing to estimate_the sizes of_their nuclei.

Meteors 
For a meteor, the standard_distance_for measurement of magnitudes is at_an_altitude of  at the observer's_zenith.

See_also_
 Hertzsprung–Russell diagram – relates_absolute magnitude or luminosity versus spectral_color or surface temperature.
 Jansky radio astronomer's preferred unit_– linear in_power/unit area
 List of most_luminous_stars
_Photographic magnitude
 Surface brightness – the magnitude for extended objects
_Zero point_(photometry) – the_typical calibration point for star flux

References

External links 
 Reference