Visibility of Luna and Lunar Crescent

'I}lus $e ae$c len$h cd be dalualed whelever $e fieoelical sidlh lr'
€xcecds the mi.ioM width ,/, visible acording b YalloPt q'lalue ctn'rion oi our s_
value criterion, for $. palticular lalues of ARCV In $c Fis 5. l l the *8nent [D or
AC is the ninimm width lil- at dv ARCV inlisibl€ according to Yallop's cliterion
The scgnenl AB is rhe thorcdcal widlh ltl" at fie cenrE of fie cresccr! Al sngular
spaBrion vr from tbc centre olc€sent ED equh4(nrl/" 'lheefore the ponnt on
rhe ouler linb oi rlc cresceni tbal las dguhr separaion fon cerrc geal$ ihan
s. = ZDOA should noi be visibl€ TIE lisiblc cls€ then crtnds fom D o D' @d
has letrBlh 2!rn. One should nole lhal Nheneve! ttl" (nininum vhible wid$ accordnr8 b
Yallop s nitrion) is Srearer tan ttlq ($coetical widtb) {5 1 13) can nor bc sed ind the
cresceDi isnotlisible, ie iihas m lengdr'
The tr1odel developed nl this Nork lo cotrlpute tlB lenglhoflhe crcsccnl hrs been
applied lo a nuobc. ol ob*rvalions lepon'd in IneralE (Schaeffd 1984 Ylllop'
1998) Tbe resuls foi ihe crescenl length against lhe elongatio' also kno*n as irc of
lighl orARCL,ae ptscnled in lable 51 1and in Fig t'l2 Tlre loBlhs mcalculaFd
by scleciing lhc nnrinum vhiblc Nidrh Vn of dcscenl foi tlrc valLE ofARcv 'c'ordrg
b {t.1.8) in rh€ elerv ca* and ihen usnrg (5 1 13)
The colunns or rhe hble 5 l ' I sllow rhc darc ot ob*ivirion thc @dinares of
rhe lcatioD of obseryer (Ldlilude and longitud€ Fspeclilclv) tbe rclatilc umull)
PAZ). rlre dladve .hnude (ARCV) lhe clon8alion (ARCL) of $e Moon at lhc be'(
'r:d
rinc ofobstvalion. lbllowcd bv setr1i_didetr and lhc cental widh ol cr'scnl in arc
ninules. rlt 4_valu., lhe niDimum cF$enl sidlh viiihle at lbe rclatile alritude
c.lculated lom (5.1 8) and finallt the cE$e'r lensth cdlculared usiie (5 1 11) Thetablc
is aFmged in chmnotogi@t or<lr of ob$mtio's dd co't'ains onlv Pai
of th€ conPlele
data s€l lhat hs b€en used for conpaine mod'ls for carli esl crescenl siehting in pe!'ous
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