SLA_RDPLAN

Apparent [α, δ] of Planet

ACTION:
Approximate topocentric apparent [α, δ] and angular size of a planet.
CALL:
CALL sla_RDPLAN (DATE, NP, ELONG, PHI, RA, DEC, DIAM)
GIVEN:

DATE

D

MJD of observation (JD−2400000.5)

NP

I

planet:

  1 = Mercury

  2 = Venus

  3 = Moon

  4 = Mars

  5 = Jupiter

  6 = Saturn

  7 = Uranus

  8 = Neptune

  9 = Pluto

else = Sun

ELONG,PHI

D

observer’s longitude (east +ve) and latitude (radians)


RETURNED:

RA,DEC

D

topocentric apparent [α, δ] (radians)

DIAM

D

angular diameter (equatorial, radians)


NOTES:
(1)
The date is in a dynamical time scale (TDB, formerly ET) and is in the form of a Modified Julian Date (JD−2400000.5). For all practical purposes, TT can be used instead of TDB, and for many applications UT will do (except for the Moon).
(2)
The longitude and latitude allow correction for geocentric parallax. This is a major effect for the Moon, but in the context of the limited accuracy of the present routine its effect on planetary positions is small (negligible for the outer planets). Geocentric positions can be generated by appropriate use of the routines sla_DMOON and sla_PLANET.
(3)
The direction accuracy (arcsec, 1000-3000 AD) is of order:
Sun 5
Mercury 2
Venus 10
Moon 30
Mars 50
Jupiter 90
Saturn 90
Uranus 90
Neptune 10
Pluto 1   (1885-2099 AD only)

The angular diameter accuracy is about 0.4% for the Moon, and 0.01% or better for the Sun and planets. For more information on accuracy, refer to the routines sla_PLANET and sla_DMOON, which the present routine uses.