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Eliminating JD: precession() now uses TT expressed in J2000 days.

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This commit is contained in:
Don Cross
2019-04-15 10:03:34 -04:00
parent a3f899e234
commit bcd37239bb
2 changed files with 18 additions and 18 deletions
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18
generate/template/astronomy.js
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@@ -631,16 +631,16 @@ function CalcMoon(T) {
};
}
function precession(jd_tdb1, pos1, jd_tdb2) {
function precession(tt1, pos1, tt2) {
var xx, yx, zx, xy, yy, zy, xz, yz, zz;
var eps0 = 84381.406;
var t, psia, omegaa, chia, sa, ca, sb, cb, sc, cc, sd, cd;
if ((jd_tdb1 != T0) && (jd_tdb2 != T0))
throw 'One of the two epochs must be J2000.0.';
if ((tt1 !== 0) && (tt2 !== 0))
throw 'One of (tt1, tt2) must be 0.';
t = (jd_tdb2 - jd_tdb1) / 36525;
if (jd_tdb2 === T0)
t = (tt2 - tt1) / 36525;
if (tt2 === 0)
t = -t;
psia = (((((- 0.0000000951 * t
@@ -685,7 +685,7 @@ function precession(jd_tdb1, pos1, jd_tdb2) {
yz = -sc * cb * ca - sa * cc;
zz = -sc * cb * sa + cc * ca;
if (jd_tdb2 == T0)
if (tt2 == 0)
{
// Perform rotation from epoch to J2000.0.
return [
@@ -812,7 +812,7 @@ function geo_pos(time, observer) {
const gast = gmst + tilt.ee/3600;
const pos1 = terra(observer, gast).pos;
const pos2 = nutation(time, -1, pos1);
const pos3 = precession(time.jd_tt, pos2, T0);
const pos3 = precession(time.tt, pos2, 0);
return pos3;
}
@@ -993,7 +993,7 @@ Astronomy.SkyPos = function(gc_vector, observer) { // based on NOVAS place()
let j2000_radec = vector2radec(j2000_vector);
let pos7 = precession(T0, j2000_vector, gc_vector.t.jd_tt);
let pos7 = precession(0, j2000_vector, gc_vector.t.tt);
let ofdate_vector = nutation(gc_vector.t, 0, pos7);
let ofdate_radec = vector2radec(ofdate_vector);
@@ -1022,7 +1022,7 @@ Astronomy.GeoMoon = function(date) {
var mpos1 = ecl2equ_vec(time, gepos);
// Convert from mean equinox of date to J2000...
var mpos2 = precession(time.jd_tt, mpos1, T0);
var mpos2 = precession(time.tt, mpos1, 0);
return { t:time, x:mpos2[0], y:mpos2[1], z:mpos2[2] };
}

18
source/js/astronomy.js
View File

@@ -1321,16 +1321,16 @@ function CalcMoon(T) {
};
}
function precession(jd_tdb1, pos1, jd_tdb2) {
function precession(tt1, pos1, tt2) {
var xx, yx, zx, xy, yy, zy, xz, yz, zz;
var eps0 = 84381.406;
var t, psia, omegaa, chia, sa, ca, sb, cb, sc, cc, sd, cd;
if ((jd_tdb1 != T0) && (jd_tdb2 != T0))
throw 'One of the two epochs must be J2000.0.';
if ((tt1 !== 0) && (tt2 !== 0))
throw 'One of (tt1, tt2) must be 0.';
t = (jd_tdb2 - jd_tdb1) / 36525;
if (jd_tdb2 === T0)
t = (tt2 - tt1) / 36525;
if (tt2 === 0)
t = -t;
psia = (((((- 0.0000000951 * t
@@ -1375,7 +1375,7 @@ function precession(jd_tdb1, pos1, jd_tdb2) {
yz = -sc * cb * ca - sa * cc;
zz = -sc * cb * sa + cc * ca;
if (jd_tdb2 == T0)
if (tt2 == 0)
{
// Perform rotation from epoch to J2000.0.
return [
@@ -1502,7 +1502,7 @@ function geo_pos(time, observer) {
const gast = gmst + tilt.ee/3600;
const pos1 = terra(observer, gast).pos;
const pos2 = nutation(time, -1, pos1);
const pos3 = precession(time.jd_tt, pos2, T0);
const pos3 = precession(time.tt, pos2, 0);
return pos3;
}
@@ -1683,7 +1683,7 @@ Astronomy.SkyPos = function(gc_vector, observer) { // based on NOVAS place()
let j2000_radec = vector2radec(j2000_vector);
let pos7 = precession(T0, j2000_vector, gc_vector.t.jd_tt);
let pos7 = precession(0, j2000_vector, gc_vector.t.tt);
let ofdate_vector = nutation(gc_vector.t, 0, pos7);
let ofdate_radec = vector2radec(ofdate_vector);
@@ -1712,7 +1712,7 @@ Astronomy.GeoMoon = function(date) {
var mpos1 = ecl2equ_vec(time, gepos);
// Convert from mean equinox of date to J2000...
var mpos2 = precession(time.jd_tt, mpos1, T0);
var mpos2 = precession(time.tt, mpos1, 0);
return { t:time, x:mpos2[0], y:mpos2[1], z:mpos2[2] };
}