# 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

`precess` `jprecess` `bprecess`

## 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
 47.74408

\$gb
 -8.909108
```

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