Distance¶

class
astropy.coordinates.
Distance
(value=None, unit=None, z=None, cosmology=None, distmod=None, parallax=None, dtype=None, copy=True, order=None, subok=False, ndmin=0, allow_negative=False)[source]¶ Bases:
astropy.units.quantity.SpecificTypeQuantity
A onedimensional distance.
This can be initialized in one of four ways:
A distance
value
(array or float) and aunit
A
Quantity
objectA redshift and (optionally) a cosmology.
Providing a distance modulus
 Parameters
 valuescalar or
Quantity
. The value of this distance.
 unit
UnitBase
The units for this distance, if
value
is not aQuantity
. Must have dimensions of distance. zfloat
A redshift for this distance. It will be converted to a distance by computing the luminosity distance for this redshift given the cosmology specified by
cosmology
. Must be given as a keyword argument. cosmology
Cosmology
orNone
A cosmology that will be used to compute the distance from
z
. IfNone
, the current cosmology will be used (seeastropy.cosmology
for details). distmodfloat or
Quantity
The distance modulus for this distance. Note that if
unit
is not provided, a guess will be made at the unit between AU, pc, kpc, and Mpc. parallax
Quantity
orAngle
The parallax in angular units.
 dtype
dtype
, optional See
Quantity
. copybool, optional
See
Quantity
. order{‘C’, ‘F’, ‘A’}, optional
See
Quantity
. subokbool, optional
See
Quantity
. ndminint, optional
See
Quantity
. allow_negativebool, optional
Whether to allow negative distances (which are possible is some cosmologies). Default:
False
.
 valuescalar or
 Raises
UnitsError
If the
unit
is not a distance. ValueError
If value specified is less than 0 and
allow_negative=False
.If
z
is provided with aunit
orcosmology
is provided whenz
is not given, orvalue
is given as well asz
.
Examples
>>> from astropy import units as u >>> from astropy.cosmology import WMAP5, WMAP7 >>> d1 = Distance(10, u.Mpc) >>> d2 = Distance(40, unit=u.au) >>> d3 = Distance(value=5, unit=u.kpc) >>> d4 = Distance(z=0.23) >>> d5 = Distance(z=0.23, cosmology=WMAP5) >>> d6 = Distance(distmod=24.47) >>> d7 = Distance(Distance(10 * u.Mpc)) >>> d8 = Distance(parallax=21.34*u.mas)
Attributes Summary
The distance modulus as a
Quantity
The parallax angle as an
Angle
objectShort for
self.compute_z()
Methods Summary
compute_z
([cosmology])The redshift for this distance assuming its physical distance is a luminosity distance.
Attributes Documentation

z
¶ Short for
self.compute_z()
Methods Documentation

compute_z
(cosmology=None)[source]¶ The redshift for this distance assuming its physical distance is a luminosity distance.
 Parameters
 cosmology
Cosmology
orNone
The cosmology to assume for this calculation, or
None
to use the current cosmology (seeastropy.cosmology
for details).
 cosmology
 Returns
 zfloat
The redshift of this distance given the provided
cosmology
.