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 year

ID I day in year (1 = Jan 1st)

FD R fraction of day

RETURNED:

$$[\,x,y,z,\dot{x},\dot{y},\dot{z}\,]$$ PV

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 routine sla_EVP.