# glactc: Convert between celestial and Galactic (or Supergalactic)... In astrolibR: Astronomy Users Library

## Description

Convert between celestial and Galactic (or Supergalactic) coordinates

## Usage

 1 glactc(ra, dec, year, gl, gb, j, degree=FALSE, fk4 = FALSE, supergalactic = FALSE)

## Arguments

 ra Right Ascension (j=1) or Galactic longitude (j=2), in decimal hours or degrees, scalar or vector dec Declination (j=1) or Galactic latitude (j=2), in degrees, scalar or vector year equinox of ra and dec, scalar gl Galactic longitude or Right Ascension, in degrees, scalar or vector gb Galactic latitude or Declination, in degrees, scalar or vector j integer indicator, direction of conversion 1: ra,dec –> gl,gb 2: gl,gb –> ra,dec degree if set, then the RA parameter (both input and output) is given in degrees rather than hours (default=FALSE) fk4 if set, then the celestial (RA, Dec) coordinates are assumed to be input/output in the FK4 system. By default, coordinates are assumed to be in the FK5 system. (default=FALSE) supergalactic if set, the function returns SuperGalactic coordinates (see details). (default=FALSE)

## Details

If j=1, this function converts proper motion in equatorial coordinates (ra,dec) to proper motion in Galactic coordinates (gl, gb) or Supergalactic Coordinates (sgl,sgb). If j=2, the conversion is reversed from Galactic/Supergalactic coordinates to equatorial coordinates. The calculation includes precession on the coordinates.

For B1950 coordinates, set fk4=TRUE and year=1950.

If supergalactic=TRUE is set, Supergalactic coordinates are defined by de Vaucouleurs et al. (1976) to account for the local supercluster. The North pole in Supergalactic coordinates has Galactic coordinates l = 47.47, b = 6.32, and the origin is at Galactic coordinates l = 137.37, b = 0.00.

## Value

 ra Galactic longitude (j=1) or Right Ascension (j=2), in decimal hours or degrees, scalar or vector dec Galactic latitude (j=1) or Declination (j=2), in degrees, scalar or vector

## Author(s)

FORTRAN subroutine by T. A. Nagy, 1978. Conversion to IDL, R. S. Hill, STX, 1987.

R adaptation by Arnab Chakraborty June 2013

## Examples

 1 2 3 4 # Find the Galactic coordinates of Altair (RA (J2000): 19 50 47 Dec (J2000): 08 52 06) # Result: gl = 47.74, gb = -8.91 glactc(ten(19,50,47), ten(8,52,6), 2000, gl, gb, 1)

### Example output

\$gl
[1] 47.74408

\$gb
[1] -8.909108

astrolibR documentation built on May 2, 2019, 3:26 a.m.