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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 [α,δ] 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 0s.03 at worst, but is usually better than 0s.01.

For applications requiring higher accuracy, see the sla_EVP and sla_EPV routines.