CL_eph_sun

Description

• Computes Earth-Sun position and velocity vectors in the ECI or EOD frame

  The default output frame is ECI.

  The model used can optionaly be modified:

  - model = "med": MEEUS "med" model is used.

  - model = "high": VSOP87 "high" model is used.

• Note: If the output frame is ECI and the model is "med", a simplified frame conversion model is used.

  The accuracy of this simplified frame conversion is better than 1 arcsecond in the [2000-2100] period, which is way below the accuracy of the model itself.

• See Reference frames for more details on the ECI and EOD frames, and Ephemerides for more details on the models.

Parameters

cjd:

Modified (1950.0) julian day (Time scale: TREF) (1xN)

tt_tref:

TT-TREF [seconds]. Default is %CL_TT_TREF. (1xN or 1x1)

frame:

(optional, string) Name of the output frame. Can be "EOD" or "ECI". Default is "ECI" (1x1)

model :

(optional, string) Accuracy of the model. "med" or "high". Default is "med". (1x1)

pos_sun :

Earth-Sun position vector in output frame [m] (3xN)

vel_sun :

Earth-Sun velocity vector in output frame [m/s] (3xN)

Bibliography

• Astronomical Algorithms J.Meeus - Second edition 1998, Chapter 25

Authors

• CNES - DCT/SB

See also

• CL_eph_planet

• CL_eph_de405

Examples

cjd = CL_dat_cal2cjd(2010,02,03,05,35,25); // Default = standard precision, in ECI frame pos_sun_ECI = CL_eph_sun(cjd) // Higher precision, in EOD frame, with velocity [pos_sun_EOD, vel_sun_EOD] = CL_eph_sun(cjd , frame="EOD", model="high");