Dust Maps

Euler/Precess

Precessing Equatorial Coordinates:

One may precess equatorial coordinates (RA, DEC) from one equinox to another in IDL in the following way:

IDL> ra = 260.871
IDL> dec = -26.205
IDL> precess, ra, dec, 1950, 2000
IDL> print, ra, dec
261.64708 -26.247309

Converting Equatorial to Galactic coordinates:

Now that (RA,DEC) are equinox 2000, they may be converted to Galactic (l,b) using the IDL procedure EULER. Note that this same routine used to assume equinox 1950! The interactive version presents six conversion options:

IDL> euler, ra, dec, l, b

1 RA-DEC (J2000) to Galactic
2 Galactic to RA-DEC(J2000)
3 RA-DEC (J2000) to Ecliptic
4 Ecliptic to RA-DEC(J2000)
5 Ecliptic to Galactic
6 Galactic to Ecliptic
Enter selection:
1

Or, one may use the non-interactive version:

IDL> euler, ra, dec, l, b, 1

IDL> print, l, b
0.00022251011 5.0003257

Reading Reddening Map:

Now the reddening value for these coordinates can be obtained:

IDL> value = dust_getval(l, b, /interp)
IDL> print,value
1.20908

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