Visibility of Luna and Lunar Crescent

fomulE. by Nunins sphdicEl 6gL at Q to b. idr egle McNallv rejeded Dmjoo s
dSmcnt ed 6ing fou-Pafl fomuh adiv6 .l:
(5.1)
Nlserically, for small ddgtes d sd a thee is onlv . muejn't dillemce b'lsFn lhe lso
Esults. Generally thc .lonsation (4) cd be cahulaled and the cre$ent l'nrth (2o) is
obede.!. e the rw fomuls 6 b. LPd lo find fi' dclici'ncv arc' Hosder' ro
calcul.rc the c6..1 lenelh nonc of these @ be ued- McNally daetoPs a fomula fot
angula! rpdlion 9 ftoD a cusp in tems ofclescent width R d:
I
SinE
-T *t'
t Rl
(5.r r)
nininum lisibl. *id$ n.sured ih ddid dn€cdon 'wtv
lron dE
disc. Thercforc the logh of th€ ce*ent h€ oblaits is l8O0 _ 29
Usiry (he Blackqell $rcshold con(6t Sutan (sultan 2oo5) adres at tlE
ninimun vhibG *id$ (in |ems of didetcr of rh' smalld eqlival€nl Blackselr
(Bhckstll, 1946) di*) of c@enl ar Frigee dd apoge al his l@rion of ob$Parion'
Tbe fomula rhal hc deleloped for calculali'8 thc crc$61 lenglh rsi
,=f!1.'to"
l2t )
o.l4)
whde r h th€ sdldidetd of tbe Moo[ md
o5