Astropy Glossary#


A parenthesized number followed by a comma denotes a tuple with one element. The trailing comma distinguishes a one-element tuple from a parenthesized n. This is from NumPy; see


<Class>-like is an instance of the Class or a valid initializer argument for Class as Class(value). E.g. Quantity-like includes "2 *" because astropy.units.Quantity("2 *") works.

[‘physical type’]#

The physical type of a quantity can be annotated in square brackets following a Quantity (or similar quantity-like).

For example, distance : quantity-like ['length']


quantity-like and a valid initializer for Angle. The unit must be an angular. A string input is interpreted as an angle as described in the Angle documentation.


Object that implements Python’s buffer protocol.


BaseCoordinateFrame subclass instance, or a SkyCoord (or subclass) instance, or a valid initializer as described in COORD.

file-like (readable)#

file-like object object that supports reading with a method read.

For a formal definition see ReadableFileLike.

file-like (writeable)#

file-like object object that supports writing with a method write.

For a formal definition see WriteableFileLike.


BaseCoordinateFrame subclass or subclass instance or a valid Frame name (string).


quantity-like and a valid initializer for Distance. The unit must be a convertible to a unit of length.


Any scalar numeric type. e.g. float or int or numpy.number.


Quantity (or subclass) instance, a number or array-like object, or a string which is a valid initializer for Quantity.

For a formal definition see QuantityLike.


Table (or subclass) instance or valid initializer for Table as described in Constructing a Table. Common types include dict[list], list[dict], list[list], and ndarray (structured array).


Time (or subclass) instance or a valid initializer for Time, e.g. str, array-like[str], datetime, or datetime64.


UnitBase subclass instance or a string or other valid initializer for Unit.

Optional Packages’ Glossary#


Any valid Matplotlib color.