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# Reference/API

Note

astropy.units.deprecated was deprecated in v7.1 and will be removed in a future version.

## astropy.units Package

This subpackage contains classes and functions for defining and converting between different physical units, as well as the units themselves.

This code is adapted from the pynbody units module written by Andrew Pontzen, who has granted the Astropy project permission to use the code under a BSD license.

### Functions

`add_enabled_aliases`(aliases) | Add aliases for units.
`add_enabled_equivalencies`(equivalencies) | Adds to the equivalencies enabled in the unit registry.
`add_enabled_units`(units) | Adds to the set of units enabled in the unit registry.
`allclose`(a, b[, rtol, atol, equal_nan]) | Whether two arrays are element-wise equal within a tolerance.
`beam_angular_area`(beam_area) | Convert between the `beam` unit, which is commonly used to express the area of a radio telescope resolution element, and an area on the sky.
`brightness_temperature`(frequency[, beam_area]) | Defines the conversion between Jy/sr and "brightness temperature", \(T_B\), in Kelvins.
`def_physical_type`(unit, name) | Add a mapping between a unit and the corresponding physical type(s).
`def_unit`(s[, represents, doc, format, ...]) | Define a new unit.
`dimensionless_angles`() | Allow angles to be equivalent to dimensionless (with 1 rad = 1 m/m = 1).
`doppler_optical`(rest) | Return the equivalency pairs for the optical convention for velocity.
`doppler_radio`(rest) | Return the equivalency pairs for the radio convention for velocity.
`doppler_redshift`() | Returns the equivalence between Doppler redshift (unitless) and radial velocity.
`doppler_relativistic`(rest) | Return the equivalency pairs for the relativistic convention for velocity.
`get_current_unit_registry`() |
`get_physical_type`(obj) | Return the physical type that corresponds to a unit (or another physical type representation).
`isclose`(a, b[, rtol, atol, equal_nan]) | Return a boolean array where two arrays are element-wise equal within a tolerance.
`logarithmic`() | Allow logarithmic units to be converted to dimensionless fractions.
`magnetic_flux_field`([mu_r]) | Convert magnetic field between magnetic field strength \((\mathbf{H})\) and magnetic flux density \((\mathbf{B})\) using the relationship:
`mass_energy`() | Returns a list of equivalence pairs that handle the conversion between mass and energy.
`molar_mass_amu`() | Returns the equivalence between amu and molar mass.
`parallax`() | Returns a list of equivalence pairs that handle the conversion between parallax angle and distance.
`pixel_scale`(pixscale) | Convert between pixel distances (in units of `pix`) and other units, given a particular `pixscale`.
`plate_scale`(platescale) | Convert between lengths (to be interpreted as lengths in the focal plane) and angular units with a specified `platescale`.
`quantity_input`([func]) | A decorator for validating the units of arguments to functions.
`set_enabled_aliases`(aliases) | Set aliases for units.
`set_enabled_equivalencies`(equivalencies) | Sets the equivalencies enabled in the unit registry.
`set_enabled_units`(units) | Sets the units enabled in the unit registry.
`spectral`() | Returns a list of equivalence pairs that handle spectral wavelength, wave number, frequency, and energy equivalencies.
`spectral_density`(wav[, factor]) | Returns a list of equivalence pairs that handle spectral density with regard to wavelength and frequency.
`temperature`() | Convert degrees Celsius and degrees Fahrenheit here because Unit and CompositeUnit cannot do addition or subtraction properly.
`temperature_energy`() | Convert between Kelvin and keV(eV) to an equivalent amount.
`thermodynamic_temperature`(frequency[, T_cmb]) | Defines the conversion between Jy/sr and "thermodynamic temperature", \(T_{CMB}\), in Kelvins.
`zero_point_flux`(flux0) | An equivalency for converting linear flux units ("maggys") defined relative to a standard source into a standardized system.

### Classes

`CompositeUnit`(scale, bases, powers[, ...]) | Create a composite unit using expressions of previously defined units.
`Decibel`(value[, unit, dtype, copy, order, ...]) |
`DecibelUnit`([physical_unit, function_unit]) | Logarithmic physical units expressed in dB.
`Dex`(value[, unit, dtype, copy, order, ...]) |
`DexUnit`([physical_unit, function_unit]) | Logarithmic physical units expressed in magnitudes.
`Equivalency`(equiv_list[, name, kwargs]) | A container for a units equivalency.
`FunctionQuantity`(value[, unit, dtype, copy, ...]) | A representation of a (scaled) function of a number with a unit.
`FunctionUnitBase`([physical_unit, function_unit]) | Abstract base class for function units.
`IrreducibleUnit`(st[, doc, format, namespace]) | Irreducible units are the units that all other units are defined in terms of.
`LogQuantity`(value[, unit, dtype, copy, ...]) | A representation of a (scaled) logarithm of a number with a unit.
`LogUnit`([physical_unit, function_unit]) | Logarithmic unit containing a physical one.
`MagUnit`([physical_unit, function_unit]) | Logarithmic physical units expressed in magnitudes.
`Magnitude`(value[, unit, dtype, copy, order, ...]) |
`NamedUnit`(st[, doc, format, namespace]) | The base class of units that have a name.
`PhysicalType`(unit, physical_types) | Represents the physical type(s) that are dimensionally compatible with a set of units.
`PrefixUnit`([s, represents, format, ...]) | A unit that is simply a SI-prefixed version of another unit.
`Quantity`(value[, unit, dtype, copy, order, ...]) | A `Quantity` represents a number with some associated unit.
`QuantityInfo`([bound]) | Container for meta information like name, description, format.
`QuantityInfoBase`([bound]) |
`SpecificTypeQuantity`(value[, unit, dtype, ...]) | Superclass for Quantities of specific physical type.
`StructuredUnit`(units[, names]) | Container for units for a structured Quantity.
`Unit`([s, represents, format, namespace, ...]) | The main unit class.
`UnitBase`() | Abstract base class for units.
`UnitConversionError` | Used specifically for errors related to converting between units or interpreting units in terms of other units.
`UnitParserWarning` | Unit parser warnings
`UnitPrefix`(symbols, names, factor) | Prefix for representing multiples or sub-multiples of units.
`UnitScaleError` | Used to catch the errors involving scaled units, which are not recognized by FITS format.
`UnitTypeError` | Used specifically for errors in setting to units not allowed by a class.
`UnitsError` | The base class for unit-specific exceptions.
`UnitsWarning` | The base class for unit-specific warnings.
`UnrecognizedUnit`(st[, doc, format, namespace]) | A unit that did not parse correctly.

### Class Inheritance Diagram

## astropy.units.si Module

This package defines the SI units. They are also available in (and should be used through) the `astropy.units` namespace.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`a` | annum (a) | \(\mathrm{365.25\,d}\) | `annum` | Yes
`A` | ampere: base unit of electric current in SI |  | `ampere`, `amp` | Yes
`Angstrom` | ångström: 10 ** -10 m | \(\mathrm{0.1\,nm}\) | `AA`, `angstrom`, `Å` | Yes
`arcmin` | arc minute: angular measurement | \(\mathrm{0.016666667\,{}^{\circ}}\) | `arcminute` | Yes
`arcsec` | arc second: angular measurement | \(\mathrm{0.00027777778\,{}^{\circ}}\) | `arcsecond` | Yes
`Bq` | becquerel: unit of radioactivity | \(\mathrm{\frac{1}{s}}\) | `becquerel` | Yes
`C` | coulomb: electric charge | \(\mathrm{A\,s}\) | `coulomb` | Yes
`cd` | candela: base unit of luminous intensity in SI |  | `candela` | Yes
`Ci` | curie: unit of radioactivity | \(\mathrm{3.7 \times 10^{10}\,Bq}\) | `curie` | Yes
`cm` | cm: 0.01 m in SI, base unit of length in cgs | \(\mathrm{0.01\,m}\) | `centimeter` | No
`d` | day (d) | \(\mathrm{24\,h}\) | `day` | Yes
`deg` | degree: angular measurement 1/360 of full rotation | \(\mathrm{0.017453293\,rad}\) | `degree` | Yes
`deg_C` | Degrees Celsius |  | `Celsius` | No
`F` | Farad: electrical capacitance | \(\mathrm{\frac{C}{V}}\) | `Farad`, `farad` | Yes
`fortnight` | fortnight | \(\mathrm{2\,wk}\) |  | No
`g` | gram (g) | \(\mathrm{0.001\,kg}\) | `gram` | Yes
`Gy` | gray: absorbed dose of ionizing radiation or kinetic energy released per unit mass (kerma) | \(\mathrm{\frac{J}{kg}}\) | `gray` | Yes
`h` | hour (h) | \(\mathrm{3600\,s}\) | `hour`, `hr` | Yes
`H` | Henry: inductance | \(\mathrm{\frac{Wb}{A}}\) | `Henry`, `henry` | Yes
`ha` | hectare: unit of area, used to express area of land | \(\mathrm{10000\,m^{2}}\) | `hectare` | No
`hourangle` | hour angle: angular measurement with 24 in a full circle | \(\mathrm{15\,{}^{\circ}}\) |  | No
`Hz` | Frequency | \(\mathrm{\frac{1}{s}}\) | `Hertz`, `hertz` | Yes
`J` | Joule: energy | \(\mathrm{N\,m}\) | `Joule`, `joule` | Yes
`K` | Kelvin: temperature with a null point at absolute zero. |  | `Kelvin` | Yes
`kat` | katal: catalytic activity. | \(\mathrm{\frac{mol}{s}}\) | `katal` | Yes
`kg` | kilogram: base unit of mass in SI. |  | `kilogram` | No
`l` | liter: metric unit of volume | \(\mathrm{1000\,cm^{3}}\) | `L`, `ℓ`, `liter` | Yes
`lm` | lumen: luminous flux | \(\mathrm{cd\,sr}\) | `lumen` | Yes
`lx` | lux: luminous emittance | \(\mathrm{\frac{lm}{m^{2}}}\) | `lux` | Yes
`m` | meter: base unit of length in SI |  | `meter` | Yes
`mas` | milli arc second: angular measurement | \(\mathrm{0.001\,{}^{\prime\prime}}\) |  | No
`micron` | micron: alias for micrometer (um) | \(\mathrm{\mu m}\) |  | No
`min` | minute (min) | \(\mathrm{60\,s}\) | `minute` | Yes
`mol` | mole: amount of a chemical substance in SI. |  | `mole` | Yes
`N` | Newton: force | \(\mathrm{\frac{kg\,m}{s^{2}}}\) | `Newton`, `newton` | Yes
`Ohm` | Ohm: electrical resistance | \(\mathrm{\frac{V}{A}}\) | `ohm`, `Ω` | Yes
`Pa` | Pascal: pressure | \(\mathrm{\frac{J}{m^{3}}}\) | `Pascal`, `pascal` | Yes
`%` | percent: one hundredth of unity, factor 0.01 | \(\mathrm{0.01}\) | `pct` | No
`rad` | radian: angular measurement of the ratio between the length on an arc and its radius |  | `radian` | Yes
`s` | second: base unit of time in SI. |  | `second` | Yes
`S` | Siemens: electrical conductance | \(\mathrm{\frac{A}{V}}\) | `Siemens`, `siemens` | Yes
`sday` | Sidereal day (sday) is the time of one rotation of the Earth. | \(\mathrm{86164.091\,s}\) |  | No
`sr` | steradian: unit of solid angle in SI | \(\mathrm{rad^{2}}\) | `steradian` | Yes
`Sv` | sievert: equivalent dose of ionizing radiation | \(\mathrm{\frac{J}{kg}}\) | `sievert` | Yes
`t` | Metric tonne | \(\mathrm{1000\,kg}\) | `tonne` | No
`T` | Tesla: magnetic flux density | \(\mathrm{\frac{Wb}{m^{2}}}\) | `Tesla`, `tesla` | Yes
`uas` | micro arc second: angular measurement | \(\mathrm{1 \times 10^{-6}\,{}^{\prime\prime}}\) | `µas`, `μas` | No
`V` | Volt: electric potential or electromotive force | \(\mathrm{\frac{J}{C}}\) | `Volt`, `volt` | Yes
`W` | Watt: power | \(\mathrm{\frac{J}{s}}\) | `Watt`, `watt` | Yes
`Wb` | Weber: magnetic flux | \(\mathrm{V\,s}\) | `Weber`, `weber` | Yes
`wk` | week (wk) | \(\mathrm{7\,d}\) | `week` | No
`yr` | year (yr) | \(\mathrm{365.25\,d}\) | `year` | Yes

## astropy.units.cgs Module

This package defines the CGS units. They are also available in (and should be used through) the `astropy.units` namespace.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`abC` | abcoulomb: CGS (EMU) of charge | \(\mathrm{Bi\,s}\) | `abcoulomb` | No
`Ba` | Barye: CGS unit of pressure | \(\mathrm{\frac{g}{cm\,s^{2}}}\) | `Barye`, `barye` | Yes
`Bi` | Biot: CGS (EMU) unit of current | \(\mathrm{\frac{cm^{1/2}\,g^{1/2}}{s}}\) | `Biot`, `abA`, `abampere` | No
`C` | coulomb: electric charge | \(\mathrm{A\,s}\) | `coulomb` | No
`cd` | candela: base unit of luminous intensity in SI |  | `candela` | No
`cm` | cm: 0.01 m in SI, base unit of length in cgs | \(\mathrm{0.01\,m}\) | `centimeter` | No
`D` | Debye: CGS unit of electric dipole moment | \(\mathrm{3.3333333 \times 10^{-30}\,C\,m}\) | `Debye`, `debye` | Yes
`deg_C` | Degrees Celsius |  | `Celsius` | No
`dyn` | dyne: CGS unit of force | \(\mathrm{\frac{cm\,g}{s^{2}}}\) | `dyne` | Yes
`erg` | erg: CGS unit of energy | \(\mathrm{\frac{cm^{2}\,g}{s^{2}}}\) |  | Yes
`Fr` | Franklin: CGS (ESU) unit of charge | \(\mathrm{\frac{cm^{3/2}\,g^{1/2}}{s}}\) | `Franklin`, `statcoulomb`, `statC`, `esu` | No
`g` | gram (g) | \(\mathrm{0.001\,kg}\) | `gram` | No
`G` | Gauss: CGS unit for magnetic field | \(\mathrm{0.0001\,T}\) | `Gauss`, `gauss` | Yes
`Gal` | Gal: CGS unit of acceleration | \(\mathrm{\frac{cm}{s^{2}}}\) | `gal` | Yes
`K` | Kelvin: temperature with a null point at absolute zero. |  | `Kelvin` | No
`k` | kayser: CGS unit of wavenumber | \(\mathrm{\frac{1}{cm}}\) | `Kayser`, `kayser` | Yes
`mol` | mole: amount of a chemical substance in SI. |  | `mole` | No
`Mx` | Maxwell: CGS unit for magnetic flux | \(\mathrm{1 \times 10^{-8}\,Wb}\) | `Maxwell`, `maxwell` | No
`Oe` | Oersted: CGS unit for magnetic field strength | \(\mathrm{79.577472\,\frac{A}{m}}\) | `Oersted`, `oersted` | Yes
`P` | poise: CGS unit of dynamic viscosity | \(\mathrm{\frac{g}{cm\,s}}\) | `poise` | Yes
`rad` | radian: angular measurement of the ratio between the length on an arc and its radius |  | `radian` | No
`s` | second: base unit of time in SI. |  | `second` | No
`sr` | steradian: unit of solid angle in SI | \(\mathrm{rad^{2}}\) | `steradian` | No
`St` | stokes: CGS unit of kinematic viscosity | \(\mathrm{\frac{cm^{2}}{s}}\) | `stokes` | Yes
`statA` | statampere: CGS (ESU) unit of current | \(\mathrm{\frac{Fr}{s}}\) | `statampere` | No

## astropy.units.astrophys Module

This package defines the astrophysics-specific units. They are also available in (and should be used through) the `astropy.units` namespace.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`adu` | adu |  |  | Yes
`AU` | astronomical unit: approximately the mean Earth–Sun distance. | \(\mathrm{1.4959787 \times 10^{11}\,m}\) | `au`, `astronomical_unit` | Yes
`beam` | beam |  |  | Yes
`bin` | bin |  |  | Yes
`chan` | chan |  |  | Yes
`ct` | count (ct) |  | `count` | Yes
`DN` | dn (DN) |  | `dn` | No
`earthMass` | Earth mass | \(\mathrm{5.9721679 \times 10^{24}\,kg}\) | `M_earth`, `Mearth` | No
`earthRad` | Earth radius | \(\mathrm{6378100\,m}\) | `R_earth`, `Rearth` | No
`electron` | Number of electrons |  |  | No
`foe` | foe or Bethe: 1e51 erg, used to measure energy emitted by a supernova | \(\mathrm{1 \times 10^{51}\,\frac{cm^{2}\,g}{s^{2}}}\) | `Bethe`, `bethe` | No
`jupiterMass` | Jupiter mass | \(\mathrm{1.8981246 \times 10^{27}\,kg}\) | `M_jup`, `Mjup`, `M_jupiter`, `Mjupiter` | No
`jupiterRad` | Jupiter radius | \(\mathrm{71492000\,m}\) | `R_jup`, `Rjup`, `R_jupiter`, `Rjupiter` | No
`Jy` | Jansky: spectral flux density | \(\mathrm{1 \times 10^{-26}\,\frac{W}{Hz\,m^{2}}}\) | `Jansky`, `jansky` | Yes
`lsec` | Light second | \(\mathrm{2.9979246 \times 10^{8}\,m}\) | `lightsecond` | No
`lyr` | Light year | \(\mathrm{9.4607305 \times 10^{15}\,m}\) | `lightyear` | Yes
`pc` | parsec: approximately 3.26 light-years. | \(\mathrm{3.0856776 \times 10^{16}\,m}\) | `parsec` | Yes
`ph` | photon (ph) |  | `photon` | Yes
`R` | Rayleigh: photon flux | \(\mathrm{7.9577472 \times 10^{8}\,\frac{ph}{s\,sr\,m^{2}}}\) | `Rayleigh`, `rayleigh` | Yes
`solLum` | Solar luminance | \(\mathrm{3.828 \times 10^{26}\,W}\) | `L_sun`, `Lsun` | No
`solMass` | Solar mass | \(\mathrm{1.9884099 \times 10^{30}\,kg}\) | `M_sun`, `Msun` | No
`solRad` | Solar radius | \(\mathrm{6.957 \times 10^{8}\,m}\) | `R_sun`, `Rsun` | No
`Sun` | Sun |  |  | No

## astropy.units.misc Module

This package defines miscellaneous units. They are also available in (and should be used through) the `astropy.units` namespace.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`bar` | bar: pressure | \(\mathrm{100000\,Pa}\) |  | Yes
`barn` | barn: unit of area used in HEP | \(\mathrm{1 \times 10^{-28}\,m^{2}}\) | `barn` | Yes
`bit` | b (bit) |  | `b` | Yes
`byte` | B (byte) | \(\mathrm{8\,bit}\) | `B` | Yes
`cycle` | cycle: angular measurement, a full turn or rotation | \(\mathrm{6.2831853\,rad}\) | `cy` | No
`eV` | Electron Volt | \(\mathrm{1.6021766 \times 10^{-19}\,J}\) | `electronvolt` | Yes
`M_e` | Electron mass | \(\mathrm{9.1093837 \times 10^{-31}\,kg}\) |  | No
`M_p` | Proton mass | \(\mathrm{1.6726219 \times 10^{-27}\,kg}\) |  | No
`pix` | pixel (pix) |  | `pixel` | Yes
`Ry` | Rydberg: Energy of a photon whose wavenumber is the Rydberg constant | \(\mathrm{13.605693\,eV}\) | `rydberg` | Yes
`spat` | spat: the solid angle of the sphere, 4pi sr | \(\mathrm{12.566371\,sr}\) | `sp` | No
`Torr` | Unit of pressure based on an absolute scale, now defined as exactly 1/760 of a standard atmosphere | \(\mathrm{133.32237\,Pa}\) | `torr` | Yes
`u` | Unified atomic mass unit | \(\mathrm{1.6605391 \times 10^{-27}\,kg}\) | `Da`, `Dalton` | Yes
`vox` | voxel (vox) |  | `voxel` | Yes

## astropy.units.function.units Module

This package defines units that can also be used as functions of other units. If called, their arguments are used to initialize the corresponding function unit (e.g., `u.mag(u.ct/u.s)`). Note that the prefixed versions cannot be called, as it would be unclear what, e.g., `u.mmag(u.ct/u.s)` would mean.

It also defines a few commonly used magnitude unit instances, like STmag, for which the physical units are defined in `astropy.units.photometric`.

All units are also available in (and should be used through) the `astropy.units` namespace.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`dB` | Decibel: ten per base 10 logarithmic unit | \(\mathrm{0.1\,dex}\) | `decibel` | No
`dex` | Dex: Base 10 logarithmic unit |  |  | No
`mag` | Astronomical magnitude: -2.5 per base 10 logarithmic unit | \(\mathrm{-0.4\,dex}\) |  | Yes

Available Magnitude Units
Unit | Description | Represents
--- | --- | ---
`STmag` | ST magnitude: STmag=-21.1 corresponds to \(1 \; \mathrm{\frac{erg}{\mathring{A}\,s\,cm^{2}}}\) | mag(ST)
`ABmag` | AB magnitude: ABmag=-48.6 corresponds to \(1 \; \mathrm{\frac{erg}{Hz\,s\,cm^{2}}}\) | mag(AB)
`M_bol` | Absolute bolometric magnitude: M_bol=0 corresponds to \(\mathrm{3.0128 \times 10^{28}\,W}\) | mag(Bol)
`m_bol` | Apparent bolometric magnitude: m_bol=0 corresponds to \(\mathrm{2.3975101 \times 10^{25}\,\frac{W}{pc^{2}}}\) | mag(bol)

## astropy.units.photometric Module

This module defines magnitude zero points and related photometric quantities.

The corresponding magnitudes are given in the description of each unit. (the actual definitions are in `astropy.units.function.units`).

Both the units and magnitudes are available in (and should be used through) the `astropy.units` namespace.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`AB` | AB magnitude zero flux density (magnitude `ABmag`). | \(\mathrm{3.6307805 \times 10^{-20}\,\frac{erg}{Hz\,s\,cm^{2}}}\) | `ABflux` | No
`Bol` | Luminosity corresponding to absolute bolometric magnitude zero (magnitude `M_bol`). | \(\mathrm{3.0128 \times 10^{28}\,W}\) | `L_bol` | No
`bol` | Irradiance corresponding to apparent bolometric magnitude zero (magnitude `m_bol`). | \(\mathrm{2.3975101 \times 10^{25}\,\frac{W}{pc^{2}}}\) | `f_bol` | No
`mgy` | Maggies - a linear flux unit that is the flux for a mag=0 object.To tie this onto a specific calibrated unit system, the zero_point_flux equivalency should be used. |  | `maggy` | Yes
`ST` | ST magnitude zero flux density (magnitude `STmag`). | \(\mathrm{3.6307805 \times 10^{-9}\,\frac{erg}{\mathring{A}\,s\,cm^{2}}}\) | `STflux` | No

### Functions

`zero_point_flux`(flux0) | An equivalency for converting linear flux units ("maggys") defined relative to a standard source into a standardized system.

## astropy.units.imperial Module

Colloquially used Imperial units.

These units are available in the `astropy.units.imperial` namespace, but not in the top-level `astropy.units` namespace, e.g.:

    >>> import astropy.units as u
    >>> mph = u.imperial.mile / u.hour
    >>> mph
    Unit("mi / h")

To include them in `compose` and the results of `find_equivalent_units`, do:

    >>> import astropy.units as u
    >>> u.imperial.enable()

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`ac` | International acre | \(\mathrm{43560\,ft^{2}}\) | `acre` | No
`BTU` | British thermal unit | \(\mathrm{1.0550559\,kJ}\) | `btu` | No
`cal` | Thermochemical calorie: pre-SI metric unit of energy | \(\mathrm{4.184\,J}\) | `calorie` | No
`cup` | U.S. | \(\mathrm{0.5\,pint}\) |  | No
`deg_F` | Degrees Fahrenheit |  | `Fahrenheit` | No
`deg_R` | Rankine scale: absolute scale of thermodynamic temperature | \(\mathrm{0.55555556\,K}\) | `Rankine` | No
`foz` | U.S. | \(\mathrm{0.125\,cup}\) | `fluid_oz`, `fluid_ounce` | No
`ft` | International foot | \(\mathrm{12\,inch}\) | `foot` | No
`fur` | Furlong | \(\mathrm{660\,ft}\) | `furlong` | No
`gallon` | U.S. | \(\mathrm{3.7854118\,\mathcal{l}}\) |  | No
`hp` | Electrical horsepower | \(\mathrm{745.69987\,W}\) | `horsepower` | No
`inch` | International inch | \(\mathrm{2.54\,cm}\) |  | No
`kcal` | Calorie: colloquial definition of Calorie | \(\mathrm{1000\,cal}\) | `Cal`, `Calorie`, `kilocal`, `kilocalorie` | No
`kip` | Kilopound: force | \(\mathrm{1000\,lbf}\) | `kilopound` | No
`kn` | nautical unit of speed: 1 nmi per hour | \(\mathrm{\frac{nmi}{h}}\) | `kt`, `knot`, `NMPH` | No
`lb` | International avoirdupois pound: mass | \(\mathrm{16\,oz}\) | `lbm`, `pound` | No
`lbf` | Pound: force | \(\mathrm{\frac{ft\,slug}{s^{2}}}\) |  | No
`mi` | International mile | \(\mathrm{5280\,ft}\) | `mile` | No
`mil` | Thousandth of an inch | \(\mathrm{0.001\,inch}\) | `thou` | No
`nmi` | Nautical mile | \(\mathrm{1852\,m}\) | `nauticalmile`, `NM` | No
`oz` | International avoirdupois ounce: mass | \(\mathrm{28.349523\,g}\) | `ounce` | No
`pint` | U.S. | \(\mathrm{0.5\,quart}\) |  | No
`psi` | Pound per square inch: pressure | \(\mathrm{\frac{lbf}{inch^{2}}}\) |  | No
`quart` | U.S. | \(\mathrm{0.25\,gallon}\) |  | No
`slug` | slug: mass | \(\mathrm{32.174049\,lb}\) |  | No
`st` | International avoirdupois stone: mass | \(\mathrm{14\,lb}\) | `stone` | No
`tbsp` | U.S. | \(\mathrm{0.5\,foz}\) | `tablespoon` | No
`ton` | International avoirdupois ton: mass | \(\mathrm{2000\,lb}\) |  | No
`tsp` | U.S. | \(\mathrm{0.33333333\,tbsp}\) | `teaspoon` | No
`yd` | International yard | \(\mathrm{3\,ft}\) | `yard` | No

## astropy.units.cds Module

This package defines units used in the CDS format, both the units defined in Centre de Données astronomiques de Strasbourg Standards for Astronomical Catalogues 2.0 format and the complete set of supported units. This format is used by VOTable up to version 1.2.

These units are not available in the top-level `astropy.units` namespace. To use these units, you must import the `astropy.units.cds` module:

    >>> from astropy.units import cds
    >>> q = 10. * cds.lyr

To include them in `compose` and the results of `find_equivalent_units`, do:

    >>> from astropy.units import cds
    >>> cds.enable()

Note, however, that this can introduce conflicts between CDS and other units in the top-level namespace. A safer way to use CDS units is to enable them inside a context manager. For instance, you could do the following if you have a string that uses CDS units:

    >>> import astropy.units as u
    >>> unit_string = "mmHg"
    >>> with cds.enable():
    ...     pressure_unit = u.Unit(unit_string)
    >>> (720*pressure_unit).to(u.bar)
    <Quantity 0.95992119 bar>

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
`%` | percent | \(\mathrm{\%}\) |  | No
`---` | dimensionless and unscaled | \(\mathrm{}\) | `-` | No
`\h` | Planck constant | \(\mathrm{6.6260701 \times 10^{-34}\,J\,s}\) |  | Yes
`A` | Ampere | \(\mathrm{A}\) |  | Yes
`a` | year | \(\mathrm{a}\) |  | Yes
`a0` | Bohr radius | \(\mathrm{5.2917721 \times 10^{-11}\,m}\) |  | Yes
`al` | Light year | \(\mathrm{lyr}\) |  | Yes
`alpha` | Fine structure constant | \(\mathrm{0.0072973526}\) |  | Yes
`Angstrom` | Angstrom | \(\mathrm{\mathring{A}}\) | `Å`, `Angstroem`, `AA` | Yes
`arcmin` | minute of arc | \(\mathrm{{}^{\prime}}\) | `arcm` | Yes
`arcsec` | second of arc | \(\mathrm{{}^{\prime\prime}}\) | `arcs` | Yes
`atm` | atmosphere | \(\mathrm{101325\,Pa}\) |  | Yes
`AU` | astronomical unit | \(\mathrm{AU}\) | `au` | Yes
`bar` | bar | \(\mathrm{bar}\) |  | Yes
`barn` | barn | \(\mathrm{barn}\) |  | Yes
`bit` | bit | \(\mathrm{bit}\) |  | Yes
`byte` | byte | \(\mathrm{byte}\) |  | Yes
`C` | Coulomb | \(\mathrm{C}\) |  | Yes
`c` | speed of light | \(\mathrm{2.9979246 \times 10^{8}\,\frac{m}{s}}\) |  | Yes
`cal` | calorie | \(\mathrm{4.1854\,J}\) |  | Yes
`cd` | candela | \(\mathrm{cd}\) |  | Yes
`Crab` | Crab (X-ray) flux |  |  | Yes
`ct` | count | \(\mathrm{ct}\) |  | Yes
`D` | Debye (dipole) | \(\mathrm{D}\) |  | Yes
`d` | Julian day | \(\mathrm{d}\) |  | Yes
`deg` | degree | \(\mathrm{{}^{\circ}}\) | `°`, `degree` | Yes
`dyn` | dyne | \(\mathrm{dyn}\) |  | Yes
`e` | electron charge | \(\mathrm{1.6021766 \times 10^{-19}\,C}\) |  | Yes
`eps0` | electric constant | \(\mathrm{8.8541878 \times 10^{-12}\,\frac{F}{m}}\) |  | Yes
`erg` | erg | \(\mathrm{erg}\) |  | Yes
`eV` | electron volt | \(\mathrm{eV}\) |  | Yes
`F` | Farad | \(\mathrm{F}\) |  | Yes
`G` | Gravitation constant | \(\mathrm{6.6743 \times 10^{-11}\,\frac{m^{3}}{kg\,s^{2}}}\) |  | Yes
`g` | gram | \(\mathrm{g}\) |  | Yes
`gauss` | Gauss | \(\mathrm{G}\) |  | Yes
`geoMass` | Earth mass | \(\mathrm{M_{\oplus}}\) | `Mgeo` | Yes
`H` | Henry | \(\mathrm{H}\) |  | Yes
`h` | hour | \(\mathrm{h}\) |  | Yes
`hr` | hour | \(\mathrm{h}\) |  | Yes
`Hz` | Hertz | \(\mathrm{Hz}\) |  | Yes
`inch` | inch | \(\mathrm{0.0254\,m}\) |  | Yes
`J` | Joule | \(\mathrm{J}\) |  | Yes
`JD` | Julian day | \(\mathrm{d}\) |  | Yes
`jovMass` | Jupiter mass | \(\mathrm{M_{\rm J}}\) | `Mjup` | Yes
`Jy` | Jansky | \(\mathrm{Jy}\) |  | Yes
`K` | Kelvin | \(\mathrm{K}\) |  | Yes
`k` | Boltzmann | \(\mathrm{1.380649 \times 10^{-23}\,\frac{J}{K}}\) |  | Yes
`l` | litre | \(\mathrm{\mathcal{l}}\) |  | Yes
`lm` | lumen | \(\mathrm{lm}\) |  | Yes
`Lsun` | solar luminosity | \(\mathrm{L_{\odot}}\) | `solLum` | Yes
`lx` | lux | \(\mathrm{lx}\) |  | Yes
`lyr` | Light year | \(\mathrm{lyr}\) |  | Yes
`m` | meter | \(\mathrm{m}\) |  | Yes
`mag` | magnitude | \(\mathrm{mag}\) |  | Yes
`mas` | millisecond of arc | \(\mathrm{marcsec}\) |  | No
`me` | electron mass | \(\mathrm{9.1093837 \times 10^{-31}\,kg}\) |  | Yes
`min` | minute | \(\mathrm{min}\) |  | Yes
`MJD` | Julian day | \(\mathrm{d}\) |  | Yes
`mmHg` | millimeter of mercury | \(\mathrm{133.32239\,Pa}\) |  | Yes
`mol` | mole | \(\mathrm{mol}\) |  | Yes
`mp` | proton mass | \(\mathrm{1.6726219 \times 10^{-27}\,kg}\) |  | Yes
`mu0` | magnetic constant | \(\mathrm{1.2566371 \times 10^{-6}\,\frac{N}{A^{2}}}\) | `µ0` | Yes
`muB` | Bohr magneton | \(\mathrm{9.2740101 \times 10^{-24}\,\frac{J}{T}}\) |  | Yes
`N` | Newton | \(\mathrm{N}\) |  | Yes
`Ohm` | Ohm | \(\mathrm{\Omega}\) |  | Yes
`Pa` | Pascal | \(\mathrm{Pa}\) |  | Yes
`pc` | parsec | \(\mathrm{pc}\) |  | Yes
`ph` | photon | \(\mathrm{ph}\) |  | Yes
`pi` | π | \(\mathrm{3.1415927}\) |  | Yes
`pix` | pixel | \(\mathrm{pix}\) |  | Yes
`ppm` | parts per million | \(\mathrm{1 \times 10^{-6}}\) |  | Yes
`R` | gas constant | \(\mathrm{8.3144626\,\frac{J}{K\,mol}}\) |  | Yes
`rad` | radian | \(\mathrm{rad}\) |  | Yes
`Rgeo` | Earth equatorial radius | \(\mathrm{6378100\,m}\) |  | Yes
`Rjup` | Jupiter equatorial radius | \(\mathrm{71492000\,m}\) |  | Yes
`Rsun` | solar radius | \(\mathrm{R_{\odot}}\) | `solRad` | Yes
`Ry` | Rydberg | \(\mathrm{R_{\infty}}\) |  | Yes
`S` | Siemens | \(\mathrm{S}\) |  | Yes
`s` | second | \(\mathrm{s}\) | `sec` | Yes
`solMass` | solar mass | \(\mathrm{M_{\odot}}\) | `Msun` | Yes
`sr` | steradian | \(\mathrm{sr}\) |  | Yes
`Sun` | solar unit | \(\mathrm{Sun}\) |  | Yes
`T` | Tesla | \(\mathrm{T}\) |  | Yes
`t` | metric tonne | \(\mathrm{1000\,kg}\) |  | Yes
`u` | atomic mass | \(\mathrm{1.6605391 \times 10^{-27}\,kg}\) |  | Yes
`V` | Volt | \(\mathrm{V}\) |  | Yes
`W` | Watt | \(\mathrm{W}\) |  | Yes
`Wb` | Weber | \(\mathrm{Wb}\) |  | Yes
`yr` | year | \(\mathrm{a}\) |  | Yes
`µas` | microsecond of arc | \(\mathrm{\mu arcsec}\) |  | No

### Functions

`enable`() | Enable CDS units so they appear in results of `find_equivalent_units` and `compose`.

## astropy.units.physical Module

Defines the physical types that correspond to different units.

The classes and functions defined here are also available in (and should be used through) the `astropy.units` namespace.

Defined Physical Types
Physical type | Unit | Other physical type(s) with same unit
--- | --- | ---
absement | \(\mathrm{m\,s}\) |
absity | \(\mathrm{s^{2}\,m}\) |
acceleration | \(\mathrm{\frac{m}{s^{2}}}\) |
action | \(\mathrm{\frac{m^{2}\,kg}{s}}\) | angular momentum
amount of substance | \(\mathrm{mol}\) |
angle | \(\mathrm{rad}\) |
angular acceleration | \(\mathrm{\frac{rad}{s^{2}}}\) |
angular frequency | \(\mathrm{\frac{rad}{s}}\) | angular speed, angular velocity
angular momentum | \(\mathrm{\frac{m^{2}\,kg}{s}}\) | action
angular speed | \(\mathrm{\frac{rad}{s}}\) | angular frequency, angular velocity
angular velocity | \(\mathrm{\frac{rad}{s}}\) | angular frequency, angular speed
area | \(\mathrm{m^{2}}\) |
bandwidth | \(\mathrm{\frac{bit}{s}}\) |
catalytic activity | \(\mathrm{\frac{mol}{s}}\) |
chemical potential | \(\mathrm{\frac{J}{mol}}\) |
column density | \(\mathrm{\frac{1}{m^{2}}}\) |
compressibility | \(\mathrm{\frac{1}{Pa}}\) |
crackle | \(\mathrm{\frac{m}{s^{5}}}\) |
data quantity | \(\mathrm{bit}\) |
diffusivity | \(\mathrm{\frac{m^{2}}{s}}\) | kinematic viscosity
dimensionless | \(\mathrm{}\) |
dose of ionizing radiation | \(\mathrm{\frac{J}{kg}}\) | specific energy
dynamic viscosity | \(\mathrm{\frac{g}{m\,s}}\) |
electrical capacitance | \(\mathrm{F}\) |
electrical charge | \(\mathrm{C}\) |
electrical charge (EMU) | \(\mathrm{abC}\) |
electrical charge (ESU) | \(\mathrm{Fr}\) |
electrical charge density | \(\mathrm{\frac{C}{m^{3}}}\) |
electrical conductance | \(\mathrm{S}\) |
electrical conductivity | \(\mathrm{\frac{S}{m}}\) |
electrical current | \(\mathrm{A}\) |
electrical current (EMU) | \(\mathrm{Bi}\) |
electrical current (ESU) | \(\mathrm{statA}\) |
electrical current density | \(\mathrm{\frac{A}{m^{2}}}\) |
electrical dipole moment | \(\mathrm{C\,m}\) |
electrical field strength | \(\mathrm{\frac{V}{m}}\) |
electrical flux density | \(\mathrm{\frac{C}{m^{2}}}\) | polarization density, surface charge density
electrical impedance | \(\mathrm{\Omega}\) | electrical reactance, electrical resistance
electrical mobility | \(\mathrm{\frac{m^{2}}{V\,s}}\) |
electrical potential | \(\mathrm{V}\) |
electrical reactance | \(\mathrm{\Omega}\) | electrical impedance, electrical resistance
electrical resistance | \(\mathrm{\Omega}\) | electrical impedance, electrical reactance
electrical resistivity | \(\mathrm{\Omega\,m}\) |
electromagnetic field strength | \(\mathrm{\frac{H}{m}}\) | permeability
electron density | \(\mathrm{\frac{e^{-}}{m^{3}}}\) |
electron flux | \(\mathrm{\frac{e^{-}}{s\,m^{2}}}\) |
energy | \(\mathrm{J}\) | torque, work
energy density | \(\mathrm{Pa}\) | pressure, stress
energy flux | \(\mathrm{\frac{J}{s\,m^{2}}}\) | irradiance
entropy | \(\mathrm{\frac{J}{K}}\) | heat capacity
force | \(\mathrm{N}\) |
frequency | \(\mathrm{Hz}\) |
frequency drift | \(\mathrm{\frac{1}{s^{2}}}\) |
heat capacity | \(\mathrm{\frac{J}{K}}\) | entropy
illuminance | \(\mathrm{lx}\) | luminous emittance
impulse | \(\mathrm{\frac{kg\,m}{s}}\) | momentum
inductance | \(\mathrm{H}\) |
irradiance | \(\mathrm{\frac{J}{s\,m^{2}}}\) | energy flux
jerk | \(\mathrm{\frac{m}{s^{3}}}\) | jolt
jolt | \(\mathrm{\frac{m}{s^{3}}}\) | jerk
jounce | \(\mathrm{\frac{m}{s^{4}}}\) | snap
kinematic viscosity | \(\mathrm{\frac{m^{2}}{s}}\) | diffusivity
length | \(\mathrm{m}\) |
linear density | \(\mathrm{\frac{kg}{m}}\) |
luminance | \(\mathrm{\frac{cd}{m^{2}}}\) |
luminous efficacy | \(\mathrm{\frac{lm}{W}}\) |
luminous emittance | \(\mathrm{lx}\) | illuminance
luminous flux | \(\mathrm{lm}\) |
luminous intensity | \(\mathrm{cd}\) |
magnetic field strength | \(\mathrm{\frac{A}{m}}\) |
magnetic flux | \(\mathrm{Wb}\) |
magnetic flux density | \(\mathrm{T}\) |
magnetic helicity | \(\mathrm{Wb^{2}}\) |
magnetic moment | \(\mathrm{m^{2}\,A}\) |
magnetic reluctance | \(\mathrm{\frac{1}{H}}\) |
mass | \(\mathrm{g}\) |
mass attenuation coefficient | \(\mathrm{\frac{m^{2}}{kg}}\) | opacity
mass density | \(\mathrm{\frac{kg}{m^{3}}}\) |
mass flux | \(\mathrm{\frac{kg}{s\,m^{2}}}\) | momentum density
molality | \(\mathrm{\frac{mol}{kg}}\) |
molar concentration | \(\mathrm{\frac{mol}{m^{3}}}\) |
molar conductivity | \(\mathrm{\frac{m^{2}\,S}{mol}}\) |
molar heat capacity | \(\mathrm{\frac{J}{K\,mol}}\) |
molar volume | \(\mathrm{\frac{m^{3}}{mol}}\) |
moment of inertia | \(\mathrm{m^{2}\,kg}\) |
momentum | \(\mathrm{\frac{kg\,m}{s}}\) | impulse
momentum density | \(\mathrm{\frac{kg}{s\,m^{2}}}\) | mass flux
number density | \(\mathrm{\frac{1}{m^{3}}}\) |
opacity | \(\mathrm{\frac{m^{2}}{kg}}\) | mass attenuation coefficient
particle flux | \(\mathrm{\frac{1}{s\,m^{2}}}\) |
permeability | \(\mathrm{\frac{H}{m}}\) | electromagnetic field strength
permittivity | \(\mathrm{\frac{F}{m}}\) |
photon flux | \(\mathrm{R}\) |
photon flux density | \(\mathrm{\frac{ph}{Hz\,s\,cm^{2}}}\) |
photon flux density wav | \(\mathrm{\frac{ph}{\mathring{A}\,s\,cm^{2}}}\) |
photon surface brightness | \(\mathrm{\frac{ph}{Hz\,s\,sr\,cm^{2}}}\) |
photon surface brightness wav | \(\mathrm{\frac{ph}{\mathring{A}\,s\,sr\,cm^{2}}}\) |
plate scale | \(\mathrm{\frac{rad}{m}}\) |
polarization density | \(\mathrm{\frac{C}{m^{2}}}\) | electrical flux density, surface charge density
pop | \(\mathrm{\frac{m}{s^{6}}}\) | pounce
pounce | \(\mathrm{\frac{m}{s^{6}}}\) | pop
power | \(\mathrm{W}\) | radiant flux
power density | \(\mathrm{\frac{J}{s\,m^{3}}}\) | spectral flux density wav
pressure | \(\mathrm{Pa}\) | energy density, stress
radiance | \(\mathrm{\frac{W}{sr\,m^{2}}}\) |
radiant flux | \(\mathrm{W}\) | power
radiant intensity | \(\mathrm{\frac{W}{sr}}\) |
reaction rate | \(\mathrm{\frac{mol}{s\,m^{3}}}\) |
snap | \(\mathrm{\frac{m}{s^{4}}}\) | jounce
solid angle | \(\mathrm{sr}\) |
specific energy | \(\mathrm{\frac{J}{kg}}\) | dose of ionizing radiation
specific entropy | \(\mathrm{\frac{J}{K\,kg}}\) | specific heat capacity
specific heat capacity | \(\mathrm{\frac{J}{K\,kg}}\) | specific entropy
specific volume | \(\mathrm{\frac{m^{3}}{kg}}\) |
spectral flux density | \(\mathrm{Jy}\) |
spectral flux density wav | \(\mathrm{\frac{J}{s\,m^{3}}}\) | power density
speed | \(\mathrm{\frac{m}{s}}\) | velocity
stress | \(\mathrm{Pa}\) | energy density, pressure
surface brightness | \(\mathrm{\frac{Jy}{sr}}\) |
surface brightness wav | \(\mathrm{\frac{J}{s\,sr\,m^{3}}}\) |
surface charge density | \(\mathrm{\frac{C}{m^{2}}}\) | electrical flux density, polarization density
surface mass density | \(\mathrm{\frac{kg}{m^{2}}}\) |
surface tension | \(\mathrm{\frac{m^{2}\,W}{Hz}}\) |
temperature | \(\mathrm{K}\) |
temperature gradient | \(\mathrm{\frac{K}{m}}\) |
thermal conductance | \(\mathrm{\frac{W}{K}}\) |
thermal conductivity | \(\mathrm{\frac{W}{K\,m}}\) |
thermal resistance | \(\mathrm{\frac{K}{W}}\) |
thermal resistivity | \(\mathrm{\frac{K\,m}{W}}\) |
time | \(\mathrm{s}\) |
torque | \(\mathrm{J}\) | energy, work
velocity | \(\mathrm{\frac{m}{s}}\) | speed
volume | \(\mathrm{m^{3}}\) |
volumetric flow rate | \(\mathrm{\frac{m^{3}}{s}}\) |
volumetric rate | \(\mathrm{\frac{1}{s\,m^{3}}}\) |
wavenumber | \(\mathrm{\frac{1}{m}}\) |
work | \(\mathrm{J}\) | energy, torque
yank | \(\mathrm{\frac{N}{s}}\) |

### Functions

`def_physical_type`(unit, name) | Add a mapping between a unit and the corresponding physical type(s).
`get_physical_type`(obj) | Return the physical type that corresponds to a unit (or another physical type representation).

### Classes

`PhysicalType`(unit, physical_types) | Represents the physical type(s) that are dimensionally compatible with a set of units.

### Class Inheritance Diagram

## astropy.units.format Package

A collection of different unit formats.

General usage is by their name in the |Unit| constructor or in the `to_string()` method, i.e., these classes rarely if ever need to be imported directly.

### Functions

`get_format`([format]) | Get a formatter by name.

### Classes

`CDS`(*args, **kwargs) | Support the Centre de Données astronomiques de Strasbourg Standards for Astronomical Catalogues 2.0 format, and the complete set of supported units.
`FITS`(*args, **kwargs) | The FITS standard unit format.
`OGIP`(*args, **kwargs) | Support the units in Office of Guest Investigator Programs (OGIP) FITS files.
`Base`(*args, **kwargs) | The abstract base class of all unit formats.
`Console`(*args, **kwargs) | Output-only format for to display pretty formatting at the console.
`Generic`(*args, **kwargs) | A "generic" format.
`Latex`(*args, **kwargs) | Output LaTeX to display the unit based on IAU style guidelines.
`LatexInline`(*args, **kwargs) | Output LaTeX to display the unit based on IAU style guidelines with negative powers.
`Unicode`(*args, **kwargs) | Output-only format to display pretty formatting at the console using Unicode characters.
`VOUnit`(*args, **kwargs) | The IVOA standard for units used by the VO.

### Class Inheritance Diagram

## astropy.units.required_by_vounit Module

This package defines SI prefixed units that are required by the VOUnit standard but that are rarely used in practice and liable to lead to confusion (such as `msolMass` for milli-solar mass). The units here are enabled so, e.g., `Unit('msolMass')` will just work, but to access the unit directly, use `astropy.units.required_by_vounit.msolMass` instead of the more typical idiom possible for the non-prefixed unit, `astropy.units.solMass`.

Available Units
Unit | Description | Represents | Aliases | SI Prefixes
--- | --- | --- | --- | ---
Prefixes for `solLum` | Solar luminance prefixes | \(\mathrm{3.828 \times 10^{26}\,W}\) | `L_sun`, `Lsun` | Only
Prefixes for `solMass` | Solar mass prefixes | \(\mathrm{1.9884099 \times 10^{30}\,kg}\) | `M_sun`, `Msun` | Only
Prefixes for `solRad` | Solar radius prefixes | \(\mathrm{6.957 \times 10^{8}\,m}\) | `R_sun`, `Rsun` | Only