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SLA_ECOR - RV & Time Corrns to Sun   

ACTION:
Component of Earth orbit velocity and heliocentric light time in a given direction.

CALL:
CALL sla_ECOR (RM, DM, IY, ID, FD, RV, TL)

GIVEN:

RM,DM R mean $[\,\alpha,\delta\,]$ of date (radians)
IY I year
ID I day in year (1 = Jan 1st)
FD R fraction of day

RETURNED:

RV R component of Earth orbital velocity (km s-1)
TL R component of heliocentric light time (s)

NOTES:
1.
The date and time is TDB (loosely ET) in a Julian calendar which has been aligned to the ordinary Gregorian calendar for the interval 1900 March 1 to 2100 February 28. The year and day can be obtained by calling sla_CALYD or sla_CLYD.
2.
Sign convention:
  • The velocity component is +ve when the Earth is receding from the given point on the sky.
  • The light time component is +ve when the Earth lies between the Sun and the given point on the sky.
3.
Accuracy:
  • The velocity component is usually within 0.004 km s-1 of the correct value and is never in error by more than 0.007 km s-1.
  • The error in light time correction is about $0^{\rm s}\hspace{-0.3em}.03$ at worst, but is usually better than $0^{\rm s}\hspace{-0.3em}.01$.
For applications requiring higher accuracy, see the sla_EVP routine.


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Next: SLA_EG50 - B1950 to Galactic
Up: SUBPROGRAM SPECIFICATIONS
Previous: SLA_ECMAT - Form Matrix

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