SLA_RDPLAN - Apparent $[\,\alpha,\delta\,]$ of Planet

ACTION:

Approximate topocentric apparent $[\,\alpha,\delta\,]$ and angular size of a planet.

CALL:

CALL sla_RDPLAN (DATE, NP, ELONG, PHI, RA, DEC, DIAM)

GIVEN:

DATE 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:

$$[\,\alpha,\delta\,]$$ RA,DEC

DIAM D angular diameter (equatorial, radians)

NOTES:

1.

The date is in a dynamical timescale (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, 1000-3000AD) is of order:

 		 Sun 		   5
		 Mercury 		   2
		 Venus 		 10
		 Moon 		 30
		 Mars 		 50
		 Jupiter 		 90
		 Saturn 		 90
		 Uranus 		 90
		 Neptune 		 10
		 Pluto 		  1   (1885-2099AD 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.