# What’s New in Astropy 6.1?#

## Overview#

Astropy 6.1 is a minor release that adds significant new functionality since the 6.0 release.

In particular, this release includes:

In addition to these major changes, Astropy 6.1 includes a large number of smaller improvements and bug fixes, which are described in the Full Changelog. By the numbers:

• 759 commits have been added since 6.0

• 188 issues have been closed since 6.0

• 316 pull requests have been merged since 6.0

• 54 people have contributed since 6.0

• 16 of which are new contributors

## Updated minimum Python version to 3.10#

The minimum required version of Python has been upgraded to 3.10. This is in line with the NumPy deprecation policy.

## Order-dependent angular separations now come with warnings#

Angular separation between two points depends on the point of view. For example, during a lunar eclipse and for an observer on the Earth the Sun and the Moon will be in (more-or-less) opposite directions, but at the same time for an observer at the Earth-Sun L2 point (where Gaia and James Webb Space Telescope are) the Sun and the Moon will be (more-or-less) in the same direction. The `separation()` method automatically converts a coordinate given to it to the frame of the coordinate it belongs to, so the separation can be different if the coordinates are swapped. Such transformations are now accompanied by an appropriate warning:

```>>> from astropy import units as u
>>> from astropy.coordinates import SkyCoord
>>> icrs = SkyCoord(0 * u.deg, 0 * u.deg, 10 * u.pc)
>>> gcrs = SkyCoord(0 * u.deg, 0 * u.deg, 380_000 * u.km, frame="gcrs")
>>> icrs.separation(gcrs)
<Angle 100.67116925 deg>
NonRotationTransformationWarning: transforming other coordinates from
<GCRS Frame (obstime=J2000.000, obsgeoloc=(0., 0., 0.) m,
obsgeovel=(0., 0., 0.) m / s)> to <ICRS Frame>. Angular separation can
depend on the direction of the transformation.
>>> gcrs.separation(icrs)
<Angle 0.0010732 deg>
NonRotationTransformationWarning: transforming other coordinates from
<ICRS Frame> to <GCRS Frame (obstime=J2000.000, obsgeoloc=(0., 0., 0.) m,
obsgeovel=(0., 0., 0.) m / s)>. Angular separation can depend on the
direction of the transformation.
```

The warning is not emitted if the coordinate transformation is a pure rotation because such transformations do not change the origin of the coordinate frames, so the angular separation does not depend on the order of the coordinates:

```>>> galactic = SkyCoord(0 * u.deg, 0 * u.deg, 10 * u.pc, frame="galactic")
>>> icrs.separation(galactic)
<Angle 93.14572374 deg>
>>> galactic.separation(icrs)
<Angle 93.14572374 deg>
```

It is possible to suppress the warning:

```>>> icrs.separation(gcrs, origin_mismatch="ignore")
<Angle 100.67116925 deg>
```

It is also possible to forbid non-rotation transformations:

```>>> icrs.separation(gcrs, origin_mismatch="error")
Traceback (most recent call last):
...
astropy.coordinates.errors.NonRotationTransformationError: refusing to
transform other coordinates from <GCRS Frame (obstime=J2000.000,
obsgeoloc=(0., 0., 0.) m, obsgeovel=(0., 0., 0.) m / s)> to <ICRS Frame>
because angular separation can depend on the direction of the transformation
```

Pure rotations will still succeed:

```>>> galactic.separation(icrs, origin_mismatch="error")
<Angle 93.14572374 deg>
```

## `io.ascii` uses 64-integers by default for integer columns#

`ascii` now uses a 64-bit integer field by default when reading a column of integer numeric data. This changes the default behavior on Windows and potentially 32-bit architectures. Previously on those platforms, table columns with any long integers which overflowed the 32-bit integer would be returned as string columns. The new default behavior is consistent with `numpy` v2 and `pandas`.

## Changes to semantics of `copy=` keyword arguments#

Public APIs that expose a `copy` argument and that previously set `False` as a default value now use `None` instead if `numpy` v2 or newer is installed. This is because in `numpy` v2, the meaning of the `copy` argument was changed, with `copy=False` now indicating that a copy should never be made, while `copy=None` is used for the previous meaning of “avoid a copy if possible”.

This includes:

• `astropy.units.Quantity`

• `astropy.utils.Masked`

• `astropy.table.Column`

• `astropy.time.Time`

• `astropy.coordinates.SkyCoord`

While this change ensures the default behaviour of astropy has not changed, code that explicitly passes `copy=False` to many of astropy’s classes may need adjustments where the intention was to forbid unnecessary copies but allow the ones that couldn’t be avoided. For portability across different versions of Numpy, we recommend that these instances of `False` be replaced with a `COPY_IF_NEEDED` constant defined as follow:

```COPY_IF_NEEDED = False if np.__version__.startswith("1.") else None
```

## `Cosmology` is now a `dataclass()`#

The `Cosmology` class is now a `dataclass()`. This means that the `dataclasses` machinery can be used to work with `Cosmology` objects. For example:

```>>> from dataclasses import asdict, fields, replace
>>> from astropy.cosmology import Planck18
>>> replace(Planck18, name="modified", Ob0=0.05)
FlatLambdaCDM(name='modified', ..., Ob0=0.05)
>>> asdict(Planck18)
{'name': 'Planck18', 'meta': ..., 'H0': <Quantity 67.66 km / (Mpc s)>, ...
>>> [f.name for f in fields(Planck18)]
['name', 'meta', 'H0', 'Om0', 'Ode0', 'Tcmb0', 'Neff', 'm_nu', 'Ob0']
```

Also, it is now possible to create new `Cosmology` subclasses using `make_dataclass()`:

```>>> from dataclasses import make_dataclass, field, fields
>>> from astropy.cosmology import Cosmology
>>> NewC = make_dataclass("NewC", [("newfield", float, field(default=None))],
...                       bases=(Cosmology,), frozen=True, eq=False)
>>> [f.name for f in fields(NewC)]
['name', 'meta', 'newfield']
```

## Full change log#

To see a detailed list of all changes in version 6.1, including changes in API, please see the Full Changelog.

## Contributors to the 6.1 release#

The people who have contributed to the code for this release are:

 Adam Ginsburg Albert Y. Shih Chiara Marmo Clément Robert Derek Homeier Eduardo Olinto * Eero Vaher Felipe Gameleira * Gordon Gibb * Hans Moritz Günther Henry Schreiner * Hélvio Peixoto James Davies Jero Bado Jo Bovy Kyle Conroy Larry Bradley Leo Singer Manodeep Sinha Manon Marchand Marcello Nascif Mark Taylor Marten van Kerkwijk Matteo Bachetti Maximilian Linhoff Michiel De Wilde * Mihai Cara Mridul Seth * Nathaniel Starkman Nick Murphy Ole Streicher Pey Lian Lim Piyush Sharma * Porter Averett * Prajwel Joseph Robert Queenin * Sam Holt * Sam Lee Sam Van Kooten Shaheer Ahmad * Simon Conseil Stephen Bailey * Stuart Littlefair Stuart Mumford Tanvi Pooranmal Meena * Thomas Robitaille Tom Aldcroft William Jamieson Zach Burnett * omahs *

Where a * indicates that this release contains their first contribution to astropy.