# What’s New in Astropy 4.3?¶

## Overview¶

Astropy 4.3 is a major release that … since the 4.2.x series of releases.

In particular, this release includes:

In addition to these major changes, Astropy v4.3 includes a large number of smaller improvements and bug fixes, which are described in the Full Changelog. By the numbers:

• xxx issues have been closed since v4.2

• xxx pull requests have been merged since v4.2

• xxx distinct people have contributed code

## Transformations to AltAz are now much more precise (and faster)¶

Following advice from M. K. Brewer and comparisons with accurate verification samples, the implementations for the transformations to AltAz coordinates were made much more precise (down to the milli-arcsec level). To help this, the CIRS frame has gained an observer location attribute.

Furthermore, by ensuring expensive calculations of the precession-nutation matrix are only done once, the transformations have been sped up considerably.

## Improvements in making Astropy thread-safe¶

To help use of Astropy in multi-threaded environments (e.g., with Dask), an effort has been started to make the basic infrastructure of astropy thread-safe for operations that do not explicitly change state. In particular, parsing of units and angles, and initializing leap-second tables should now be safe even when done simultaneously in multiple threads, as should any use of the lazyproperty decorator (and the lazy=True version of classproperty).

## Full change log¶

To see a detailed list of all changes in version v4.3, including changes in API, please see the Full Changelog.