eteq · Oct 27, 2011 · Oct 15, 2011 · Oct 15, 2011 · Oct 15, 2011 · Oct 15, 2011
diff --git a/astropy/constants/__init__.py b/astropy/constants/__init__.py
@@ -0,0 +1,32 @@
+"""
+Contains astronomical and physical constants for use in Astropy or other
+places.
+
+The package contains a `~astropy.constants.cgs` and `~astropy.constants.si`
+module that define constants in CGS and SI units, respectively.  A typical use
+case might be::
+
+    from astropy.constants.cgs import c
+
+    ... define the mass of something you want the rest energy of as m ...
+    E = m*c**2
+
+"""
+
+from . import cgs
+from . import si
+from .constant import Constant
+
+
+# Update the docstring to include a list of units from the si module
+__doc__ += """
+The following constants are defined in `~astropy.constants.cgs` and
+`~astropy.constants.si` .
+
+"""
+
+for nm, val in sorted(si.__dict__.iteritems()):
+    if isinstance(val, Constant):
+        __doc__ += '    * ' + nm + '\n        ' + val.name + '\n'
+del nm, val
+__doc__ += '\n'
diff --git a/astropy/constants/cgs.py b/astropy/constants/cgs.py
@@ -0,0 +1,101 @@
+# Numerical constants, in cgs units
+
+from .constant import Constant
+from . import si
+
+# PHYSICAL CONSTANTS
+
+# Planck constant
+h = Constant(si.h * 1.e7, si.h.error * 1.e7,
+             si.h.name, si.h.origin, 'erg.s')
+
+# Reduced Planck constant
+hbar = Constant(si.hbar * 1.e7, si.hbar.error * 1.e7,
+                si.hbar.name, si.hbar.origin, 'erg.s')
+
+# Boltzmann constant [CODATA]
+k_B = Constant(si.k_B * 1.e7, si.k_B.error * 1.e7,
+               si.k_B.name, si.k_B.origin, 'erg.s')
+
+# Speed of light [CODATA]
+c = Constant(si.c * 1.e2, si.c.error * 1.e2,
+             si.c.name, si.c.origin, 'cm/s')
+
+# Gravitional constant [CODATA]
+G = Constant(si.G * 1.e3, si.G.error * 1.e3,
+             si.G.name, si.G.origin, 'cm^3/g/s^2')
+
+# Proton mass [CODATA]
+m_p = Constant(si.m_p * 1.e3, si.m_p.error * 1.e3,
+               si.m_p.name, si.m_p.origin, 'g')
+
+# Neutron mass [CODATA]
+m_n = Constant(si.m_n * 1.e3, si.m_n.error * 1.e3,
+               si.m_n.name, si.m_n.origin, 'g')
+
+# Electron mass [CODATA]
+m_e = Constant(si.m_e * 1.e3, si.m_e.error * 1.e3,
+               si.m_e.name, si.m_e.origin, 'g')
+
+# Stefan-Boltzmann constant
+sigma_sb = Constant(si.sigma_sb * 1.e3, si.sigma_sb.error * 1.e3,
+                    si.sigma_sb.name, si.sigma_sb.origin,
+                    'erg/cm^2/K^4/s')
+
+# Electron charge
+e = Constant(si.e * si.c * 10., si.e.error * si.c * 10.,
+             si.e.name, si.e.origin, 'statC')
+
+# Avogadro's number
+N_A = Constant(si.N_A, si.N_A.error,
+               si.N_A.name, si.N_A.origin, '/mol')
+
+# Gas constant
+R = Constant(si.R * 1.e7, si.R.error * 1.e7,
+             si.R.name, si.R.origin, 'erg/K/mol')
+
+# DISTANCE
+
+# Astronomical Unit
+au = Constant(si.au * 1.e2, si.au.error * 1.e2,
+              si.au.name, si.au.origin, 'cm')
+
+# Parsec
+pc = Constant(si.pc * 1.e2, si.pc.error * 1.e2,
+              si.pc.name, si.pc.origin, 'cm')
+
+# Kiloparsec
+kpc = Constant(si.kpc * 1.e2, si.kpc.error * 1.e2,
+               si.kpc.name, si.kpc.origin, 'cm')
+
+# SOLAR QUANTITIES
+
+# Solar luminosity
+L_sun = Constant(si.L_sun * 1.e7, si.L_sun.error * 1.e7,
+                 si.L_sun.name, si.L_sun.origin, 'erg/s')
+
+# Solar mass
+M_sun = Constant(si.M_sun * 1.e3, si.M_sun.error * 1.e3,
+                 si.M_sun.name, si.M_sun.origin, 'g')
+
+# Solar radius
+R_sun = Constant(si.R_sun * 1.e2, si.R_sun.error * 1.e2,
+                 si.R_sun.name, si.R_sun.origin, 'cm')
+
+# OTHER SOLAR SYSTEM QUANTITIES
+
+# Jupiter mass
+M_jup = Constant(si.M_jup * 1.e3, si.M_jup.error * 1.e3,
+                 si.M_jup.name, si.M_jup.origin, 'g')
+
+# Jupiter equatorial radius
+R_jup = Constant(si.R_jup * 1.e2, si.R_jup.error * 1.e2,
+                 si.R_jup.name, si.R_jup.origin, 'cm')
+
+# Earth mass
+M_earth = Constant(si.M_earth * 1.e3, si.M_earth.error * 1.e3,
+                 si.M_earth.name, si.M_earth.origin, 'g')
+
+# Earth equatorial radius
+R_earth = Constant(si.R_earth * 1.e2, si.R_earth.error * 1.e2,
+                 si.R_earth.name, si.R_earth.origin, 'cm')
diff --git a/astropy/constants/constant.py b/astropy/constants/constant.py
@@ -0,0 +1,50 @@
+class Constant(float):
+    """A physical or astronomical constant.
+
+    Objects of this class behave just like `float` values when used in
+    expressions, but they contain additional information
+
+    Attributes
+    ----------
+    name : str
+        The name of this constant.
+    error : float
+        The uncertainty in the value of this constant.
+    origin : str
+        The source used for the value of this constant.
+    units : str
+        A string describing the units
+
+    .. warning ::
+        The `units` attribute will be replaced when the Astropy units package
+        is implemented. Don't count on it being a simple string in the future.
+
+    """
+
+    def __init__(self, value, error, name, origin, units):
+        self.error = error
+        self.name = name
+        self.origin = origin
+        self.units = units
+        return float.__init__(self, value)
+
+    def __new__(self, value, error, name, origin, units):
+        return float.__new__(self, value)
+
+    def __repr__(self):
+        s = "<Constant: "
+        s += "name='{0}' ".format(self.name)
+        s += "value={0} ".format(float.__repr__(self))
+        s += "error={0} ".format(self.error)
+        s += "units='{0}' ".format(self.units)
+        s += "origin='{0}' ".format(self.origin)
+        s += ">"
+        return s
+
+    def __str__(self):
+        s = "  Name   = {0}\n".format(self.name)
+        s += "  Value  = {0}\n".format(float.__repr__(self))
+        s += "  Error  = {0}\n".format(self.error)
+        s += "  Units = {0}\n".format(self.units)
+        s += "  Origin = {0}".format(self.origin)
+        return s
diff --git a/astropy/constants/si.py b/astropy/constants/si.py
@@ -0,0 +1,124 @@
+# Numerical constants, in cgs units
+
+import numpy
+
+from .constant import Constant
+
+# PHYSICAL CONSTANTS
+
+# Planck constant
+h = Constant(6.62606957e-34, 0.00000029e-34,
+             "Planck constant",
+             'CODATA 2010', 'J.s')
+
+# Reduced Planck constant
+hbar = Constant(h * 0.5 / numpy.pi, h.error * 0.5 / numpy.pi,
+                "Reduced Planck constant",
+                'CODATA 2010', 'J.s')
+
+# Boltzmann constant
+k_B = Constant(1.3806488e-23, 0.0000013e-23,
+               "Boltzmann constant",
+               'CODATA 2010', 'J/K')
+
+# Speed of light
+c = Constant(2.99792458e8, 0.,
+             "Speed of light in vacuum",
+             'CODATA 2010', 'm/s')
+
+# Gravitional constant
+G = Constant(6.67384e-11, 0.00080e-11,
+             "Gravitational constant",
+             'CODATA 2010', 'm^3/kg/s^2')
+
+# Proton mass
+m_p = Constant(1.672621777e-27, 0.000000074e-27,
+               "Proton mass",
+               'CODATA 2010', 'kg')
+
+# Neutron mass
+m_n = Constant(1.674927351e-27, 0.000000074e-27,
+               "Neutron mass",
+               'CODATA 2010', 'kg')
+
+# Electron mass
+m_e = Constant(9.10938291e-31, 0.00000040e-31,
+               "Electron mass",
+               'CODATA 2010', 'kg')
+
+# Stefan-Boltzmann constant
+sigma_sb = Constant(5.670373e-8, 0.000021e-8,
+                    "Stefan-Boltzmann constant",
+                    'CODATA 2010', 'W/m^2/K^4')
+
+# Electron charge
+e = Constant(1.602176565e-19, 0.000000035e-19,
+             "Electron charge",
+             'CODATA 2010', 'C')
+
+# Avogadro's number
+N_A = Constant(6.02214129e23, 0.00000027e23,
+               "Avogadro's number",
+               'CODATA 2010', '/mol')
+
+# Gas constant
+R = Constant(8.3144621, 0.0000075,
+             "Gas constant",
+             'CODATA 2010', 'J/mol/K')
+
+# DISTANCE
+
+# Astronomical Unit
+au = Constant(1.4959787066e11, 0.00000000005e11,
+              "Astronomical Unit",
+              "Allen's Astrophysical Quantities 4th Ed.", 'm')
+
+# Parsec
+pc = Constant(3.0856776e16, 0.00000005e16,
+              "Parsec",
+              "Allen's Astrophysical Quantities 4th Ed.", 'm')
+
+# Kiloparsec
+kpc = Constant(3.0856776e19, 0.00000005e19,
+              "Kiloparsec",
+              "Allen's Astrophysical Quantities 4th Ed.", 'm')
+
+# SOLAR QUANTITIES
+
+# Solar luminosity
+L_sun = Constant(3.846e26, 0.0005e26,
+                 "Solar luminosity",
+                 "Allen's Astrophysical Quantities 4th Ed.", 'W')
+
+# Solar mass
+M_sun = Constant(1.9891e30, 0.00005e30,
+                 "Solar mass",
+                 "Allen's Astrophysical Quantities 4th Ed.", 'kg')
+
+# Solar radius
+R_sun = Constant(6.95508e8, 0.00026e8,
+                 "Solar radius",
+                 "Allen's Astrophysical Quantities 4th Ed.", 'm')
+
+
+# OTHER SOLAR SYSTEM QUANTITIES
+
+# Jupiter mass
+M_jup = Constant(1.8987e27, 0.00005e27,
+                 "Jupiter mass",
+                 "Allen's Astrophysical Quantities 4th Ed.", 'kg')
+
+# Jupiter equatorial radius
+R_jup = Constant(7.1492e7, 0.00005e7,
+                 "Jupiter equatorial radius",
+                 "Allen's Astrophysical Quantities 4th Ed.", 'm')
+
+# Earth mass
+M_earth = Constant(5.9742e24, 0.00005e24,
+                  "Earth mass",
+                  "Allen's Astrophysical Quantities 4th Ed.", 'kg')
+
+# Earth equatorial radius
+R_earth = Constant(6.378136e6, 0.0000005e6,
+                   "Earth equatorial radius",
+                   "Allen's Astrophysical Quantities 4th Ed.", 'm')