Visibility of Luna and Lunar Crescent

elled th. Julid Dare abb@ialed B JD. So the ,D @Gponding lo thc 5i" 30.i. on
Ocrober 5, 2004 ar Grcenwich is 245t284.2708t11t.. Thls rhe Jutim D!i. i3. mesE
of tih. clapsd sine thn €pocl 6id is cxpEss.d in nmber of n@ eld d.y5_
The orhcr epoch of inpori,lcc lo rh€ €lftnl work k fie noncnt of dme €ell.d
J2000 0 a.d il Eprcseds lhe l2ln TDTon J.nuary l,2O0O i.€. (Abononhal Almahac,
2007). Tbe JD conesponding ro rhis hom.nt dl C@nwicb is 2451545 days. This is the
.poch or 2eo me for borh rhe Luq Th@iy ELP,2000 (Chopo.lTouz{ & Chaponr,
l9l) dd th€ pl&elary th@ry VSOP,87 {Brc|,gnon & Fmcou, 1988). In bo$ rhes
0leodcs lih. m@!red frcn J2000.0 bo foMrd od b6ct*ards. In ELP thir rimc is in
is coBidcrcd in rulian CentJies (i.c.16525 me.n sle days) md i! VSOP il is inJulie
Millemia (365250 mce solrdays).
BoththeseepocbsmbasedonrheinreRaloirimealted..toedn$hrdat, qhich
is defincd a fie int rval berween lw slccessile rhsits (r6sdge rhlough rhe locll
meddim) ofrhc fic ious body knoM as ft. mee Se. This ficlitious body novcs sirh
uifom sF.d alory lhc cel6ial cquabr .hd is consider.d in place of lh. acrul Sun $ar
oovcs vith non-unifom sped (dw ro rhe .llipli€ orbn of tne Efin) abnS lne Ectipd€.
The tmsit of $c aclual Sm over a local heridi& vdes up ro I I minurs over a penod
of on€ lrcpical ye (Astmnooical AlFanac, 2O()7), Thereby atl civil rim. reckoning
have b€eh a$ocialed with the hedn Sln lhot consisrl of 24 mean solar hous, The
beeinningofa civilday, i.e. zro hou* on civil clocks occu^ at nidniehl when the nour
dgle of rh. Mean Sun is rw€Irc hou6 lccodin8 to the local or sisddd hcidia..
Th. tiDe describ€d by lh. cl@k showing d. mm $lf rinc is not wilhoul its
di*Ep.n i6. In fd it is lhe E€rtn, $e gtob€, ilsctf rhal is ou cl@t lnd $c n.m solat
tine B suppos.d to b. basd on ths a!€ragc rate al which lhe Eadh n spinning a@und irs
dn. Howeverlhn considearion is only with rcspecl !o lh€ Med Sun. Du.lo the orbilal
noionoflh. Eanh beins in rhe sme direction as its dis ofmlolion (ton qesl lo EEst)
on€ ubl totaiion coDpldes in l6s thm ihis nee sold day. So the actuat nle of dial
rchtion is b.t r ralized by rhe No sw;sivc resirs of a sior. Dis in|cdal is lemed