lo

eponed in rhe Explanation Io the ln.lloh Attranonical EPle,cfir $al is basd oi
Schoch (Sch@b, l9l0). In allrhe* worts for dei€miriry lhe day ofrhe fi*r liribilir) ot
new cE$o! ARCV (arc ofvirion) b shoM to be a sMnd d.8Fe pohomial runcrion
of DAz (claive uinuth). The* edly €florc !rc only empnical in natuF N rhe critcria
dc!.loped de bsed on lluing rhe dau so rh8t mo$ ofthe obs.oaiions arc conshlcnl
TlE* nelhods do not hke into cosideElion lhe vidth ofcE$enl Btuii (Bruii,
1977) co.sidd rh€ ihpodahce oacE*cnt widtn fld his Dod.l desqibes ARCV (in
rems ofannud. of cr.scent above horizon plus tn€ solar depRssion belov lhe horizln)
os a funcion ofthe crescenr widtn. The Nodel ofBruio. ho\rever, kkes $e {idlh !s a
funcion ofih€ RCV ond DAz md a fircd Ddnh-Mmn dislaftc (in lemsolfixcd * i'
dirnrl'ler ol fte lu.ar disc). Hc sas ale thc fi6t \no consid.rcd phJsical .stkcs
dsociakd *nh $c problen like blightnds ofskt and thar oflhe M@n. Thus tu nrodcl
due lo Bruin is the lirsl drolelical nodelofr|t nodern timcs Using the nrodels tur thc
briShhess oalhe lull M@n as a fuhcrion of altilude (Befrporad, 190,r) lnd $c s[t
brighhe$ duri.g lNililhi (Kooncn ct al., 1952, Si€denbpl 1940) Bruin delclop lhc
visibililt cu^6 r€lnrin! the aldudc olcrc*€d sirh the slar dcpGsion. AlonS lhc$
ctrrvcs the bdehb€ss ofcrcscem (modellcd on $e basis of lirll Moo.) is al leasl ds much
os tlhl ofrhe twiliShl sky. He aho delclopcd cuNes sholvnu rel{lDn berwccn ARCV
and sl.t depesion rhll ldd prorcd to bc crucial for lunhcr nodellihg ol canics'
Yallop has edne lbr funho improvemenr ond consides cece *idth as a
funclion ofARCV. DAZ and lhe acllal scmi-dianeter ol lhe Moon (rhar depends on Lhc
Eanh-M@n disrucc) al $e time ofob6endion (Yallop. 1998). \vilh de!€lopinS a model
lor lhe besl time of yisibiht YaUop s nod.l al$ onsideF ARCV 6 a ihi.d d.gtce
polynomial tunction of $e actul cresc.nt oidrh ar the ben ime of visibihJ. Such
polynofrial is oblain.d by applying leasr square appbxination on a basic data sel This
blsic data s€l *qs d.duced bt Yallop fom lhe limiling lbibilil, .uvs of bnrin b!
slctins ARCV for a Sircn sidtn from tlr ninin@ oh lhe componding limilin8
2\