.. doctest-skip-all

.. _whatsnew-4.2:

**************************
What's New in Astropy 4.2?
**************************

Overview
========

Astropy 4.2 is a major release that adds new funcionality since the 4.1 release.

In particular, this release includes:

* :ref:`whatsnew-4.2-cosmology`
* :ref:`whatsnew-4.2-time-perf-imp`
* :ref:`whatsnew-4.2-erfa`

In addition to these major changes, Astropy v4.2 includes
smaller improvements and bug fixes and significant cleanup, which are described in the
:ref:`changelog`. By the numbers:

* 183 issues have been closed since v4.1
* 105 pull requests have been merged since v4.1
* 63 distinct people have contributed code

.. _whatsnew-4.2-cosmology:

Planck 2018 is accepted and now the default cosmology
=====================================================

The accepted version of the Planck 2018 cosmological parameters has been included
and has become the default cosmology.  It is identical to the previous, preliminary
version (Planck18_arXiv_v2), which is deprecated and will be removed in a future release.

  >>> from astropy.cosmology import Planck18
  >>> Planck18.age(0)
  <Quantity 13.7868853 Gyr>

.. _whatsnew-4.2-time-perf-imp:

Time performance improvements
=============================

The performance for creating a ``Time`` object from a large array of
fixed-format string times was dramatically improved. For ISO and ISOT formats
the speed-up is a factor of 25 and for the year day-of-year format the speedup
is a factor of 50. This is done with a new C-based time string parser which can
also be used for custom user-defined Time formats. For details see
:ref:`time-fast-c-parser`.

In addition the performance for creating a scalar ``Time`` object in a epoch
format like ``unix``, ``unix_tai``, or ``cxcsec`` was improved by a factor of 4.


.. _whatsnew-4.2-erfa:

Removed ERFA module
===================

The private ``_erfa`` module has been converted to its own package `PyeERFA
<https://pyerfa.readthedocs.io/en/latest/>`__. It is now a required
dependency of astropy, and can be directly imported with ``import
erfa``. Importing ``_erfa`` from ``astropy`` now issues a deprecation
warning and will be removed in the future.


Full change log
===============

To see a detailed list of all changes in version v4.2, including changes in
API, please see the :ref:`changelog`.


Contributors to the v4.2 release
================================

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

.. hlist::
  :columns: 4

  *    Adrian Price-Whelan
  *    Albert Y. Shih
  *    Alex Conley
  *    Aniket Sanghi  *
  *    Anne Archibald
  *    Bastian Beischer  *
  *    Ben Greiner  *
  *    Benjamin Winkel
  *    Bojan Nikolic  *
  *    Brian Soto  *
  *    Brigitta Sipőcz
  *    Bruce Merry  *
  *    Chris Simpson
  *    Chun Ly  *
  *    Clara Brasseur
  *    Clare Shanahan
  *    David Stansby
  *    Derek Homeier
  *    Diego Alonso  *
  *    Ed Slavich
  *    E. Madison Bray
  *    Erik Tollerud
  *    Erin Allard
  *    Even Rouault  *
  *    Gabriel Perren
  *    George Galvin  *
  *    Gregory Simonian  *
  *    Hannes Breytenbach
  *    Hans Moritz Günther
  *    Inada Naoki  *
  *    James Turner
  *    Jero Bado  *
  *    Juan Luis Cano Rodríguez
  *    Kris Stern
  *    Larry Bradley
  *    Lauren Glattly
  *    Lee Spitler  *
  *    Ludwig Schwardt  *
  *    Marten van Kerkwijk
  *    Matthew Craig
  *    Maximilian Nöthe
  *    Michele Costa
  *    Miguel de Val-Borro
  *    Mihai Cara
  *    Nadia Dencheva
  *    Nathaniel Starkman  *
  *    Nicolas Tessore  *
  *    Nikita Saxena  *
  *    Ole Streicher
  *    Paul Huwe  *
  *    Peter Yoachim  *
  *    Pey Lian Lim
  *    Ricardo Fonseca  *
  *    Rui Xue
  *    Shreyas Bapat
  *    Simon Conseil
  *    Stuart Littlefair
  *    Stuart Mumford
  *    Thomas Robitaille
  *    Tom Aldcroft
  *    Tom Donaldson
  *    Victoria Dye  *
  *    Zac Hatfield-Dodds  *