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RE: (meteorobs) Three questions
Hi Tom,
Please find below the answer to question one. I guess there are copy rights on the
algorithhms below, but this should not be a problem for personal use.
I hope you speak "C" !
Marc de Lignie
Dutch Meteor Society
>
>
>Greetings. I have three hopefully easy questions. Any help appreciated.
>
>1. What is the formula for determining solar longitude?
>
/*
Calculates the Julian day for a given month, day and year
Source: numerical recipes
*/
long julianday(int mm, int id, int iyyy)
{
long jul;
int ja,jy,jm;
if (iyyy == 0) {
printf("JULDAY: there is no year zero.");
exit(1);
}
if (iyyy < 0) ++iyyy;
if (mm > 2) {
jy=iyyy;
jm=mm+1;
} else {
jy=iyyy-1;
jm=mm+13;
}
jul = (long) (floor(365.25*jy)+floor(30.6001*jm)+id+1720995L);
if (id+31L*(mm+12L*iyyy) >= IGREG) {
ja=0.01*jy;
jul += 2-ja+(int) (0.25*ja);
}
return jul;
}
/*
Calculates solar longitude for equinox 2000.0, given Julian Day and Universal Time
Source: Casper ter Kuile.
Original source: Jean Meeus.
*/
float sol2000(long jul, float tut)
{
double sl,sa,te,c1,c2,c3,c,stl,omega,sal;
te=(jul-2415020L)/36525.; /* decimale eeuw vanaf 1900 */
sl = 279.69668 + 36000.76892*te + .0003025*te*te;
sa = 358.47583 + 35999.04975*te - .00015 *te*te - .0000033*te*te*te;
sl = sl - floor(sl/360.)*360.;
sa = sa - floor(sa/360.)*360.;
sa = sa*PS;
c1 = (1.91946 - .004789 * te - .000014*te*te) * sin(sa);
c2 = (.020094 - .0001*te) * sin(2.*sa);
c3 = .000293 * sin(3.*sa);
c = c1 + c2 + c3;
/*
Berekening werkelijke zonne-lengte en werkelijke anomalie
*/
stl = sl + c;
/*
Berekening schijnbare zonne-lengte
*/
omega = 259.18 - 1934.142*te;
omega = omega - floor(omega/360.)*360.;
sal = stl - .00569 - .00479 * sin(omega*PS); /* zonslengte voor 12h UT */
sal=sal+(tut-12.)/24.*360./365.25;
sal=sal - .01396 * (100.*te - 100.); /* precessie correctie */
return sal;
}
------------------------------------------------------------------------------------
Marc de Lignie
Prins Hendrikplein 42 Tel. +31 (70) 320 5673
NL-2264 SN Leidschendam Fax. +31 (70) 332 6477
The Netherlands E-mail: mcdelign@pidot net
Predicted progress always fails. Real progress is all the small
steps you realize to have made when looking back in time.
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