Skyfield

------------------------

* Times now support arithmetic: you can add or subtract from a time
either a number representing days of Terrestrial Time (TT) or a Python
``timedelta`` which Skyfield interprets as TT days and seconds.
`568 <https://github.com/skyfielders/python-skyfield/issues/568>`_

* Fixed the ``.itrs_xyz`` vector of the geographic position returned
by the :meth:`~skyfield.toposlib.Geoid.subpoint_of()` method.
`673 <https://github.com/skyfielders/python-skyfield/issues/673>`_

* Skyfield now uses HTTPS instead of FTP to download JPL ephemeris files
like ``de421.bsp``. This does risk raising an error for users whose
machines have out-of-date root certificates. But it protects the
connection from outside tampering, and will keep working if the
``ssd.jpl.nasa.gov`` FTP service is ever shut down — as happened
earlier this year to FTP on NASA’s ``cddis.nasa.gov`` server.
`666 <https://github.com/skyfielders/python-skyfield/issues/666>`_

------------------------

* Extended the :func:`~skyfield.magnitudelib.planetary_magnitude()`
routine to work with all the major planets, which upgrades it from a
prototype feature to a production feature of Skyfield.

* The :meth:`~skyfield.toposlib.Geoid.subpoint()` method has been
deprecated, because users reported that its name was a poor match for
its behavior. Four new methods have replaced it:
:meth:`~skyfield.toposlib.Geoid.latlon_of()`,
:meth:`~skyfield.toposlib.Geoid.height_of()`,
:meth:`~skyfield.toposlib.Geoid.geographic_position_of()`, and
:meth:`~skyfield.toposlib.Geoid.subpoint_of()`.
`644 <https://github.com/skyfielders/python-skyfield/issues/644>`_

* Added a timescale method :meth:`~skyfield.timelib.Timescale.linspace()`.
`617 <https://github.com/skyfielders/python-skyfield/issues/617>`_

* The :func:`~skyfield.almanac.oppositions_conjunctions()` routine,
which was originally designed only for planets, can now also handle
the Moon (which moves from opposition to conjunction much faster).

---------------------

* The
:meth:`Angle.dstr() <skyfield.units.Angle.dstr>`
and
:meth:`Angle.hstr() <skyfield.units.Angle.hstr>`
methods now accept a ``format=`` argument
that lets callers override Skyfield’s default angle formatting
and supply their own; see `Formatting angles`.
`513 <https://github.com/skyfielders/python-skyfield/issues/513>`_

* The prototype :func:`~skyfield.magnitudelib.planetary_magnitude()`
function now works not only when given a single position, but when
given a vector of several positions.

--------------------

* Replaced the old historic ∆T table from the United States Naval Observatory
with up-to-date splines from the 2020 release of the extensive research by
`Morrison, Stephenson, Hohenkerk, and Zawilski <Morrison, Stephenson, et al>`
and also adjusted the slope of Skyfield’s near-future ∆T estimates
to make the slope of ∆T much less abrupt over the coming century.

* Added a full reference frame object
for the :class:`~skyfield.sgp4lib.TEME` reference frame
used by SGP4 Earth satellite elements.

------------------------

* Added a :meth:`~skyfield.positionlib.ICRF.frame_latlon_and_rates()` method
that can compute the rates at which angles like altitude and azimuth,
or right ascension and declination,
are changing.

* Accepted a contributor’s helpful fix for a rounding error
that had slightly shifted a few constellation boundaries.
`548 <https://github.com/skyfielders/python-skyfield/issues/548>`_

* The :class:`~skyfield.timelib.Time`
tuple :data:`~skyfield.timelib.Time.utc`
and method :meth:`~skyfield.timelib.Time.utc_strftime()`
are now backed by the same math,
so they always advance to the next calendar day at the same moment.
This makes it safe to mix values returned by one of them
with values returned by the other.
`542 <https://github.com/skyfielders/python-skyfield/issues/542>`_

* Vector subtraction now returns the position subclass
specific to the resulting vector’s center.
`549 <https://github.com/skyfielders/python-skyfield/issues/549>`_

-----------------------

* Tweaked several lines of code that build NumPy arrays
to avoid a new deprecation warning
``Creating an ndarray from ragged nested sequences
(which is a list-or-tuple of lists-or-tuples-or ndarrays
with different lengths or shapes) is deprecated``.
NumPy no longer wants to accept a simple constant like ``0.0``
where the resulting array needs a whole row of zeros.
`536 <https://github.com/skyfielders/python-skyfield/issues/536>`_

* Added an :meth:`~skyfield.positionlib.ICRF.hadec()` position method that
returns hour angle and declination.
`510 <https://github.com/skyfielders/python-skyfield/issues/510>`_

* The default ``str()`` and ``repr()`` strings
for geographic positions have been streamlined,
and no longer raise ``ValueError`` when elevation is an array.
They now show simple decimals
instead of splitting degrees of longitude and latitude
into minutes and seconds;
always show elevation, even if zero;
properly format NumPy arrays;
and abbreviate long arrays.
`524 <https://github.com/skyfielders/python-skyfield/issues/524>`_

* Fixed
:meth:`Angle.dstr() <skyfield.units.Angle.dstr>`
and
:meth:`Angle.hstr() <skyfield.units.Angle.hstr>`
to return an array of strings when the angle itself is an array.
`527 <https://github.com/skyfielders/python-skyfield/issues/527>`_