Visibility of Luna and Lunar Crescent

Tbh is lhe hain rcason bcbind @nsidedng Age of Moon s not a vcry good indicabr for
dt visibilily of cF56t. In sprinS.nd Mm€r vcry t$utrg.ge cltg cd h. sn lnd
dudng th. {ullmn and *inle6 very old clescent may .scape sighling in th€ holthern
hemisphed. Thc situalion is rcveB.d s6odlly for de sud@ hmisphec,
whcn lhe M@n is wsl of fte sun (el6rial loncnudc or rh. M@n is noc rh&
$ar ofdre Sun) i. our sky it is Old Moon carching up wilh rhe Sun. The Old Cre$enr can
b. en in lhe mominss befoE lhc suriF. An r $e binh of Ncw Mmn (c.leslial
longilude of rhe Moon b*omes jusl eratd lhe rbat of lhe sun) rhe Mooi Eehes e6r
oltheSun6dcan no$ b. *njustaftssun*t. How.vn dcpending on ih. d{limrioB
olrhe Sun and the Moon and lhe localion of$e observer $e new cBcent My et well
bcfoE thc sunst in which cG it is iDFssible lo * th€ ncr crsceft Th8 the fisl and
rhc Do$ nnporLnr clilerion aor lhe visihility of the .ev.$ccm Moon is ftar the Moon
*$ an€r $c sunscl. Alknately $c cnbrio. for thc visihilily of thc l5l cd$ent is dDt
rhc Moon riss before lhe suni*.
Whcn thc cresent is very close ro th€ sun il rcmains invisiblc dE to the facl tbar
$c ohospherc close to lhe sun remains highlt illnminated evcn afi( $e sunser'
Thqefoe fi.rc n6 to be a frininum lhrcshold epaEtion or Elongarion between fic Sln
,nd rhe Moon b.loN vhich ihe crecent cannol be sen. Thh minimud o. lhrshold
eloneation varies hotuh to oond 6 fie djsrance bctween lhc Earlh and $e Moon keeps
valyine. Vhcnclossl (at apoe€e) $e Moon h tround 350000 kn lrom thc Eanh ind !l
lhe fdhat (perig€) il k aound 400000 lo. Thus a Ne\ Mon ar apogec mat be *cn
whennscbnsation fod rhc Suh is snallrnd a New Moon at periSce may nol b€ s.cn ar
nuch ld8cr elongaton. Thi. is du. ro the fst that closer is thc Mmn the lars€r dd
brigbler ir appead in oui sky ahd wheo il k farrher il appeaB saller and less biShl at
rhc se elongalion. Thts .nother inpona crir.rion is lhar $e New Mmn cm be *en
for a combinorion ofcenain optinlm valu.s ofelong ion and lhe distanccof$e Moon
fom fi. E.nh. thi! conbiMlion Esults into tlE op(nm valu€ of thc widlh orcFv€nl
A cFsenr wi$ small €longation $al appea6 lare.t md briSller al apogee may be seen