SLA_EVP - Earth Position & Velocity

From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node102.html | 149 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 149 insertions(+) create mode 100644 src/slalib/sun67.htx/node102.html (limited to 'src/slalib/sun67.htx/node102.html') diff --git a/src/slalib/sun67.htx/node102.html b/src/slalib/sun67.htx/node102.html new file mode 100644 index 0000000..d22b187 --- /dev/null +++ b/src/slalib/sun67.htx/node102.html @@ -0,0 +1,149 @@ + + + + +SLA_EVP - Earth Position & Velocity + + + + + + + + + + + + +

+ +

+
+ Next: SLA_FITXY - Fit Linear Model to Two Sets +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_EULER - Rotation Matrix from Euler Angles +

SLA_EVP - Earth Position & Velocity + +

ACTION: +: Barycentric and heliocentric velocity and position of the Earth. +
CALL: +: CALL sla_EVP (DATE, DEQX, DVB, DPB, DVH, DPH) +

GIVEN: +

+
+ + + + + + + + + +

DATE	D	TDB (formerly ET) as a Modified Julian Date +(JD-2400000.5)
DEQX	D	Julian Epoch (e.g. 2000D0) of mean equator and +equinox of the vectors returned. If DEQX <0, +all vectors are referred to the mean equator and +equinox (FK5) of date DATE.

RETURNED: +

+
+ + + + + + + + + + + + + + + + + +

DVB	D(3)	barycentric $[\,\dot{x},\dot{y},\dot{z}\,]$ , AU s^-1
DPB	D(3)	barycentric $[\,x,y,z\,]$ , AU
DVH	D(3)	heliocentric $[\,\dot{x},\dot{y},\dot{z}\,]$ , AU s^-1
DPH	D(3)	heliocentric $[\,x,y,z\,]$ , AU

NOTES: +

1. +

This routine is used when accuracy is more important +than CPU time, yet the extra complication of reading a +pre-computed ephemeris is not justified. The maximum + deviations from the JPL DE96 ephemeris are as follows: +

velocity (barycentric or heliocentric): 420 mm s^-1 +
position (barycentric): 6900 km +
position (heliocentric): 1600 km +

2. +

The routine is an adaption of the BARVEL and BARCOR + subroutines of P.Stumpff, which are described in + Astr.Astrophys.Suppl.Ser. 41, 1-8 (1980). + Most of the changes are merely cosmetic and do not affect + the results at all. However, some adjustments have been + made so as to give results that refer to the new (IAU 1976 + `FK5') equinox and precession, although the differences these + changes make relative to the results from Stumpff's original + `FK4' version are smaller than the inherent accuracy of the + algorithm. One minor shortcoming in the original routines + that has not been corrected is that slightly better + numerical accuracy could be achieved if the various polynomial + evaluations were to be so arranged that the smallest terms were + computed first. Note also that one of Stumpff's precession + constants differs by + $0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.001$ from the value given in the + Explanatory Supplement. +

+ +

+
+ Next: SLA_FITXY - Fit Linear Model to Two Sets +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_EULER - Rotation Matrix from Euler Angles +

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +

+ + -- cgit