SLA_EARTH - Approx Earth Pos/Vel

ACTION:

Approximate heliocentric position and velocity of the Earth (single precision).

CALL:

CALL sla_EARTH (IY, ID, FD, PV)

GIVEN:

IY	I	year
ID	I	day in year (1 = Jan 1st)
FD	R	fraction of day

RETURNED:

PV

R(6)

Earth $[ x,y,z,\dot{x},\dot{y},\dot{z} ]$ (AU, AU s$^{-1}$)

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. The Earth heliocentric 6-vector is referred to the FK4 mean equator and equinox of date.
3. Maximum/RMS errors 1950-2050:
   • 13/5 $\times10^{-5}$ AU = 19200/7600 km in position
   • 47/26  $\times10^{-10}$ AU s$^{-1}$ = 0.0070/0.0039 km s$^{-1}$ in speed
4. More accurate results are obtainable with the routines sla_EVP and sla_EPV.