Skyfield

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

* You can now specify the distance to an object when generating a
position from altitude and azimuth coordinates.
`158 <https://github.com/skyfielders/python-skyfield/issues/158>`_

* The dictionary of satellites returned when you read a TLE file
now supports lookup by integer satellite ID, not just by name,
and now knows how to parse TLE files from Space-Track.
`163 <https://github.com/skyfielders/python-skyfield/issues/163>`_
`167 <https://github.com/skyfielders/python-skyfield/issues/167>`_

* Star coordinates can now be offered for any epoch, not just J2000.
`166 <https://github.com/skyfielders/python-skyfield/issues/166>`_

* You can now create a time object given the UT1 date.
`91 <https://github.com/skyfielders/python-skyfield/issues/91>`_

* Fractional Julian years are now available on ``Time`` objects as ``.J``.

* The parameter DUT1 is now available on ``Time`` objects as ``.dut1``.
`176 <https://github.com/skyfielders/python-skyfield/issues/176>`_

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

* Geocentric coordinates now have a
:meth:`~skyfield.positionlib.Geocentric.subpoint()`
method that computes the latitude and longitude
of the point beneath that body.

* All of the ``Timescale`` time constructor methods now accept arrays.

* Emergency fix to stop Skyfield
from endlessly downloading new copies of ``deltat.preds``,
since the file has gone out of date at the USNO site.

* Fixed ability of a :class:`~skyfield.starlib.Star`
to be initialized with a tuple that breaks units into minutes and seconds
(broke in version 1.2).

* Issues fixed:
`170 <https://github.com/skyfielders/python-skyfield/issues/170>`_
`172 <https://github.com/skyfielders/python-skyfield/issues/172>`_

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

* The documentation now describes
how to create an excerpt of a large JPL ephemeris
without downloading the entire file.
Several Skyfield tests now run much faster
because they use an ephemeris excerpt instead of waiting for a download.

* For ``load_file()`` a leading ``~`` now means “your home directory”.

* You can now initialize a velocity from kilometers per second
with ``Velocity(km_per_s=...)``.

* Empty time and angle objects no longer raise an exception when printed.
(Thanks, JoshPaterson!)

* Issues fixed:
`160 <https://github.com/skyfielders/python-skyfield/issues/160>`_
`161 <https://github.com/skyfielders/python-skyfield/issues/161>`_
`162 <https://github.com/skyfielders/python-skyfield/issues/162>`_

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

* Positions can now be converted to AstroPy with
:meth:`~skyfield.positionlib.ICRF.to_skycoord()`.

* You can now provide a timescale of your own to an
:meth:`~skyfield.sgp4lib.EarthSatellite`
instead of having it trying to load one itself.

* Downloaded files are no longer marked as executable on Windows.

* A friendly error message, rather than an obscure traceback, is now
returned if you try converting a position to alt/az coordinates but
the position was not measured from a position on the Earth’s surface.

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

* Brought the core API to maturity: replaced the narrow concept of
building a “body” from several ephemeris segments with the general
concept of a vector function that is the sum of several simpler vector
functions.

* Added support for adding and subtracting vector functions.

* Deprecated the Earth ``topos()`` method in favor of vector addition.

* Deprecated the Earth ``satellite()`` method in favor of vector addition.

* Deprecated the body ``geometry_of()`` method in favor of vector subtraction.

* Celestrak satellite files can now be opened with ``load.tle(url_or_filename)``.

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

* Attempted to speed up Earth satellite calculations by caching a single
time scale object instead of creating a new one each time.

* Fixed a possible divide-by-zero error when applying deflection to an
apparent position.