ANN: Astropy v3.1 released

[Erik Tollerud]

Dear colleagues,

We are very happy to announce the v3.1 release of the Astropy package,
a core Python package for Astronomy:

http://www.astropy.org

Astropy is a community-driven Python package intended to contain much of
the core functionality and common tools needed for astronomy and
astrophysics. It is part of the Astropy Project, which aims to foster an
ecosystem of interoperable astronomy packages for Python.

The focus of this release is on performance, but it also contains new and
improved major functionality. Highlights include:

* Performance Improvements across-the-board
* A new sub-package for Uncertainties and Distributions
* A new Box Least Squares Periodogram
* J-style coordinates parser
* Support for use of Time and TimeDelta columns within a Table
* Array-valued Time and TimeDelta objects are now mutable
* Better uncertainty support and bit planes in NDData
* A new operator for Quantity performance
* Thermodynamic temperature equivalency
* Little-h equivalency
* Change in default cosmology
* Significant improvements in WCSAxes
* A new convenience function for imshow with ImageNormalize
* A common API for World Coordinate Systems

In addition, hundreds of smaller improvements and fixes have been made. An
overview of the changes is provided at:

    http://docs.astropy.org/en/stable/whatsnew/3.1.html

Note that the Astropy 3.x series only supports Python 3. Python 2 users can
continue to use the 2.x (LTS) series (but without new features).

Instructions for installing Astropy are provided on our website, and
extensive documentation can be found at:

    http://docs.astropy.org

If you make use of the Anaconda Python Distribution, you can update to
Astropy v3.1 with:

    conda update astropy

Whereas if you usually use pip, you can do:

    pip install astropy --upgrade

Please report any issues, or request new features via our GitHub repository:

    https://github.com/astropy/astropy/issues

Over 300 developers have contributed code to Astropy so far, and you can
find out more about the team behind Astropy here:

    http://www.astropy.org/team.html

As a reminder, Astropy v2.0 (our long term support release) will continue
to be supported with bug fixes (but no new features) until the end of 2019,
so if you need to use Astropy in a very stable environment, you may want to
consider staying on the v2.0.x set of releases (for which we have recently
released v2.0.10).

If you use Astropy directly for your work, or as a dependency to another
package, please remember to acknowledgment it by citing the appropriate
Astropy paper. For the most up-to-date suggestions, see the acknowledgement
page (http://www.astropy.org/acknowledging.html), but as of this release
the recommendation is:

This research made use of Astropy, a community-developed core Python
package for Astronomy (Astropy Collaboration, 2018).

where (Astropy Collaboration, 2018) is a reference to
https://doi.org/10.3847/1538-3881/aabc4f


Special thanks to the coordinator for this release: Brigitta Sipocz.

We hope that you enjoy using Astropy as much as we enjoyed developing it!

Erik Tollerud, Tom Robitaille, Kelle Cruz, and Tom Aldcroft
on behalf of The Astropy Collaboration