Use the doppler_optical equivalency to convert wavelength to veloctiy

Author: migueldvb

tutorials/UVES/UVES.ipynb

@@ -760,11 +760,14 @@
      "cell_type": "code",
      "collapsed": false,
      "input": [
+      "# This function uses the Doppler equivalency between wavelength and velocity\n",
+      "import astropy.units as u\n",
       "def wave2doppler(w, w0):\n",
-      "    doppler = ((w-w0)/w0 * c)\n",
-      "    return doppler\n",
+      "    w0_equiv = u.doppler_optical(w0)\n",
+      "    w_equiv = w.to(u.km/u.s, equivalencies=w0_equiv)\n",
+      "    return w_equiv\n",
       "\n",
-      "print wave2doppler(waveclosetoHa, 656.489 * u.nm).decompose().to(u.km/u.s)"
+      "print wave2doppler(waveclosetoHa, 656.489 * u.nm).decompose()"
      ],
      "language": "python",
      "metadata": {},