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Changelog

Released versions

v1.49 — 2024 June 13

v1.48 — 2024 February 7

  • Times now support the < operator, so Python can sort them.
  • For convenience, geoids like :data:`~skyfield.toposlib.wgs84` have a new attribute :data:`~skyfield.toposlib.Geoid.polar_radius`.
  • You can no longer subtract two positions unless they have the same .center. Otherwise, a ValueError is raised. This check has always been performed when you subtract vector functions, but it was missing from the position subtraction routine.
  • On days that the Sun fails to rise and set in the Arctic and Antarctic, the new rising and setting routines now correctly set the value False not only for sunrise but also for sunset.

v1.47 — 2024 January 13

v1.46 — 2023 April 9

  • The :func:`~skyfield.almanac.oppositions_conjunctions()` routine now measures ecliptic longitude using the ecliptic of each specific date, rather than always using the J2000 ecliptic, which should improve its accuracy by several seconds.
  • Skyfield’s internal table for the ∆T Earth orientation parameter has been updated, so that its predictions now extend to 2024-04-13.
  • Bugfix: Skyfield was giving values several kilometers off when computing the elevation above ground level of a target that was positioned directly above the Earth’s north or south pole.
  • Bugfix: the :func:`~skyfield.positionlib.ICRF.is_behind_earth()` method was incorrectly returning True if the Earth was on the line that joins the two satellites, but over on the far side of the other satellite where it wasn’t really in the way.
  • Internals: the :meth:`~skyfield.positionlib.ICRF.altaz()` method now lives on the main position class instead of in two specific subclasses. If the user mistakenly tries to call .altaz() on an instance of the :class:`~skyfield.positionlib.Astrometric` position subclass — which previously lacked the method — then a friendly exception is raised explaining their error.

v1.45 — 2022 September 15

  • Bugfix: minor planets and comets in Skyfield 1.44 would raise an exception if asked for a position in the half of their orbit where they are inbound towards their perihelion.

v1.44 — 2022 September 12

  • Skyfield’s internal table for the ∆T Earth orientation parameter has been updated, so that instead of including measurements only through December 2021 it now knows Earth orientation through September 2022.
  • Distance and velocity objects can now be created by calling their unit names as constructors, like d = Distance.km(5.0) and v = Velocity.km_per_s(0.343).
  • Updated the URL from which the Hipparcos database hip_main.dat is downloaded, following a change in the domain for the University of Strasbourg from u-strasbg.fr to unistra.fr.

v1.43.1 — 2022 July 6

  • An attempt at overly clever scripting resulted in a Skyfield 1.43 release without a setup.py in its .tar.gz; within an hour, a Python 2.7 user had reported that Skyfield could no longer install. This release is identical to 1.43 but (hopefully) installs correctly for everyone!

v1.43 — 2022 July 6

v1.42 — 2022 February 6

v1.41 — 2021 December 16

  • 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
  • Fixed the .itrs_xyz vector of the geographic position returned by the :meth:`~skyfield.toposlib.Geoid.subpoint_of()` method. #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

v1.40 — 2021 November 14

v1.39 — 2021 April 14

v1.38 — 2021 April 3

  • 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.

v1.37 — 2021 February 15

v1.36 — 2021 January 26

  • 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
  • Added an :meth:`~skyfield.positionlib.ICRF.hadec()` position method that returns hour angle and declination. #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
  • 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

v1.35 — 2020 December 31

v1.34 — 2020 December 10

v1.33 — 2020 November 18

  • Fix: running load.timescale(builtin=False) was raising an exception FileNotFoundError if the finals2000A.all file was not already on disk, instead of downloading the file automatically. #477

v1.32 — 2020 November 16

1.31 — 2020 October 24

  • Skyfield now uses the International Earth Rotation Service (IERS) file finals2000A.all for updated ∆T and leap seconds. The USNO is no longer updating the files deltat.data and deltat.preds that previous versions of Skyfield used, and the cddis.nasa.gov server from which they were fetched will discontinue anonymous FTP on 2020 October 31. See downloading-timescale-files. #452 #464
  • The comets dataframe built from the MPC file CometEls.txt now includes the reference column, so users can tell which orbit is most recent if there are several orbits for a single comet. (For example, the file currently lists two C/2020 F3 (NEOWISE) orbits.) The comet examples in the documentation now build a dataframe that only includes the most recent orbit for each comet. #463
  • Two new methods :meth:`~skyfield.iokit.Loader.days_old()` and :meth:`~skyfield.iokit.Loader.download()` make it simple to download a fresh copy of a file if the copy on disk is older than you would like.

1.30 — 2020 October 11

  • The various strftime() Skyfield methods now support the %j day-of-year format code.
  • Fix: the new Julian calendar support broke support for out-of-range month numbers, wrapping them into the current year instead of letting them overflow into subsequent years. #461
  • Fix: a stray debugging print() statement was stranded in t.dut1. #455
  • The :class:`~skyfield.timelib.Time` object, if manually instantiated without a Julian date fraction, now provides a fraction array with dimensions that match the Julian date argument. #458

1.29 — 2020 September 25

1.28 — 2020 September 24

  • Broken URL: Because the VizieR archive apparently decided to uncompress their copy of the hip_main.dat.gz Hipparcos catalog file, the old URL now returns a 404 error. As an emergency fix, this version of Skyfield switches to their uncompressed hip_main.dat. Hopefully they don’t compress it again and break the new URL! A more permanent solution is discussed at: #454
  • To unblock this release, removed a few deprecated pre-1.0 experiments from April 2015 in skyfield.hipparcos and skyfield.named_stars that broke because the Hipparcos catalog is no longer compressed; hopefully no one was using them.
  • In a sweeping internal change, the :meth:`~skyfield.timelib.Timescale` and :meth:`~skyfield.timelib.Time` objects now offer support for the Julian calendar that’s used by historians for dates preceding the adoption of the Gregorian calendar in 1582. See choice of calendars if you want to turn on Julian dates in your application. #450

1.27 — 2020 September 15

1.26 — 2020 August 1

  • The official ∆T files on NASA’s FTP server have stopped receiving updates — they have no new data beyond February, the start of the global pandemic. Unless they are updated by next February, older versions of Skyfield will unfortunately download the files all over again every time :meth:`~skyfield.iokit.Loader.timescale()` is called (unless the builtin=True parameter is provided). To make Skyfield less fragile going forward:
    1. The loader’s :meth:`~skyfield.iokit.Loader.timescale()` method now defaults to builtin=True, telling it to use the ∆T and leap second files that ship with Skyfield internally. To download new ∆T files from NASA and the leap second file from the International Earth Rotation Service, specify builtin=False.
    2. The concept of an “expired” file has been removed from load(). Skyfield is now much simpler: if a file with the correct name exists, Skyfield uses it. See :ref:`downloading-timescale-files` if you still want your application to check the age of your timescale files and automatically download new ones.
  • The ICRF.separation_from() method now officially supports the combination of an array of positions with a single reference position! Its previous support for that combination was, alas, accidental, and was broken with the 1.23 release. #414 #424
  • A prototype :func:`~skyfield.magnitudelib.planetary_magnitude()` routine has been added with support for several planets. #210
  • The utc timezone that Skyfield returns in Python datetimes is now either the Python Standard Library’s own UTC object, if it supplies one, or else is defined by Skyfield itself. Skyfield no longer silently tries importing the whole pytz package merely to use its UTC object — which also means that the timezone returned by Skyfield longer offers the non-standard localize() method. #413

1.25 — 2020 July 24

1.24 — 2020 July 20

1.23 — 2020 July 9

  • Added :doc:`kepler-orbits` support for generating the positions of comets and asteroids from Minor Planet Center data files.
  • Added :func:`~skyfield.positionlib.ICRF.is_behind_earth()` to determine whether a celestial object is blocked from an Earth satellite’s view by the Earth itself.
  • Replaced the awkward and hard-to-explain rough_period search parameter with the conceptually simpler step_days parameter, and updated the instructions in :doc:`searches` to match.
  • Made the :meth:`~skyfield.iokit.Loader.tle_file()` import method less strict about Earth satellite names: any text on the line before two lines of TLE data is now saved as the satellite name. A parameter skip_names=True turns this off if, for particular TLE files, this leads to unwanted text being saved.

1.22 — 2020 Jun 8

  • Skyfield’s improved time precision (stored internally as two floats) is now used in computing ephemeris positions, Earth orientation, and light-travel time, producing position angles which change much more smoothly over time on a sub-milliarcsecond scale.
  • :doc:`searches` is now documented for custom events that users define themselves, instead of only being documented for the official pre-written :doc:`almanac` functions. Not only discrete events but also maxima and minima are now officially supported and documented, thanks to a rewrite of the underlying code.
  • Time objects no longer cache the nutation and precession matrices, since they are never used again after being multiplied together to create the equinox-of-date rotation matrix. This should save 144 bytes for each time in a :class:`~skyfield.timelib.Time` array.
  • It is now possible to :ref:`from-satrec` thanks to a new Earth satellite constructor method. #384
  • Added :meth:`~skyfield.iokit.Loader.build_url()` that returns the URL from which Skyfield will download a file. #382
  • Added :meth:`~skyfield.jpllib.SpiceKernel.close()` to support applications that need to do fine-grained resource management or whose testing framework check for dangling open files. #374
  • Skyfield’s dependency list now asks for “jplephem” version 2.13 or later. Skyfield 1.21, alas, could incur a Module not found error when importing jplephem.exceptions if a user had an old “jplephem” version already installed. #386

1.21 — 2020 May 29

  • Added :func:`~skyfield.positionlib.ICRF.is_sunlit()` to determine whether Earth satellites in orbit are in Earth’s shadow or not, thanks to a pull request from Jesse Coffey.
  • Added :func:`~skyfield.positionlib.position_of_radec()` to replace the poorly designed position_from_radec().
  • Skyfield :class:`~skyfield.timelib.Time` objects now have microsecond internal accuracy, so round trips to and from Python datetimes should now preserve all the microsecond digits.
  • The :meth:`~skyfield.timelib.Time.utc_strftime()` method now rounds to the nearest minute or second if it sees that either minutes or seconds are the smallest unit of time in the format string.
  • The 6 numbers in the sequence t.utc can now be accessed by the attribute names year, month, day, hour, minute, and second.
  • Nutation routines should now be faster and have a smaller memory footprint, thanks to a rewrite that uses more optimized NumPy calls. #373
  • Thanks to Jérôme Deuchnord, the exception raised when asking for a position out-of-range of a JPL ephemeris now shows the calendar dates for which the ephemeris is valid and carries several useful attributes. #356

1.20 — 2020 April 24

  • Erik Tollerud contributed a fix for a deprecation warning about SSL from the most recent versions of Python (“cafile, cpath and cadefault are deprecated, use a custom context instead”). The file download routine now auto-detects which mechanism your Python supports. #363
  • Added an elevation_m argument to :meth:`~skyfield.planetarylib.PlanetaryConstants.build_latlon_degrees()`.

1.19 — 2020 April 23

  • To hopefully fix the SSL: CERTIFICATE_VERIFY_FAILED errors that some users encounter when downloading timescale files, Skyfield has taken the risk of switching away from your system’s SSL certificates to the certificate bundle from the certifi package. #317
  • Added a new almanac routine for finding :ref:`lunar-nodes`. #361
  • Gave geographic location objects a new itrf_xyz() method that returns their raw ITRF coordinates. #354
  • Fixed the sign of the velocity vector when two vectors are directly geometrically subtracted. #355

1.18 — 2020 March 26

1.17 — 2020 February 2

  • Upgraded to a new version of the sgp4 Python library that, when possible, uses the fast official C++ implementation of SGP4.
  • Added a :meth:`~skyfield.sgp4lib.EarthSatellite.find_events()` Earth satellite method that finds the times at which a satellite rises, culminates, and sets.
  • Improved the logic behind the :doc:`almanac` routines to avoid rare situations in which a cluster of nearly identical times would be produced for what should really be considered a single event. #333
  • Fixed the :meth:`~skyfield.timelib.Time.utc_strftime()` method so it does not report that every day in all of recorded history is a Monday. #335

1.16 — 2019 December 20

1.15 — 2019 November 20

1.14 — 2019 November 1

1.13 — 2019 October 10

  • Provided a constellation lookup routine through :func:`~skyfield.api.load_constellation_map()`.
  • Added a position_from_radec() function.
  • Fixed the apparent() method in the case where a single observer position is observing an entire vector of target positions. #229

1.12 — 2019 September 2

  • Fix: an exception was being thrown when creating a Loader pointed at a Windows directory for which Python’s os.makedirs() function returned a spurious error. #283
  • The internal reverse_terra() routine can now be given an iterations=0 argument if the caller wants geocentric latitude and longitude.

1.11 — 2019 July 22

  • You can now call load.timescale(builtin=True) to use time scale files that Skyfield carries internally, instead of downloading them. Note that the time scale files distributed with any given version of Skyfield will gradually fall out of date.
  • Fix: indexing a position now returns a position with an actual velocity. #241
  • Fix: the Star method from_dataframe() now correctly pulls stellar parallax data from the dataframe if available. #266
  • Fix: :func:`~skyfield.searchlib.find_discrete()` was generating empty arrays of search dates, upsetting the astronomy code, if the start and end dates were very close together. #240

1.10 — 2019 February 2

  • Fix: teach Skyfield the new format of the Naval Observatory ∆T data file deltat.preds, whose change in format caused Skyfield to start throwing an exception for new users. #236

1.9 — 2018 September 23

1.8 — 2018 September 12

1.7 — 2018 September 3

  • Skyfield now supports loading the Hipparcos star catalog as a Pandas dataframe, providing the user with convenient mechanisms for looking up a single star by HIP number or filtering the entire catalog by magnitude. See :doc:`stars` for details.
  • Ecliptic coordinates can now be produced for epochs other than J2000 thanks to a new optional parameter specifying the desired epoch for the ecliptic_latlon() method.
  • A position that gives a position, velocity, and time can now be converted into full osculating orbital elements through the routine :func:`~skyfield.elementslib.osculating_elements_of()`.
  • A couple of bugs in the load() routine have been fixed. #193 #194

1.6 — 2018 July 25

  • Both of the loader methods :meth:`~skyfield.iokit.Loader.open()` and tle() now accept not just URLs but also plain local file paths; they correctly re-download a remote file if “reload=True” is specified; and they allow specifying a different local “filename=” than the one at the end of the URL.
  • Earth satellite objects no longer try to instantiate a timescale object of their own, which often kicked off an unexpected download of the three files needed to build a timescale.
  • Satellite names are now correctly loaded from Space-Track TLE files.
  • The ability to create times using Julian Dates is now better advertised, thanks to dedicated timescale methods whose names end in …_jd().

1.5 — 2018 July 4

1.4 — 2018 May 20

  • You can now specify the distance to an object when generating a position from altitude and azimuth coordinates. #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 #167
  • Star coordinates can now be offered for any epoch, not just J2000. #166
  • You can now create a time object given the UT1 date. #91
  • Fractional Julian years are now available on Time objects as .J.
  • The parameter DUT1 is now available on Time objects as .dut1. #176

1.3 — 2018 April 15

  • 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 #172

1.2 — 2018 March 29

  • 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 #161 #162

1.1 — 2018 January 14

  • 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.

1.0 — 2017 March 15

  • 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).

0.9.1 — 2016 December 10

  • 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.

0.9

  • The observe() method of an observer on the Earth’s surface now correctly accounts for the way that the Earth’s gravity will deflect the apparent position of objects that are not exactly overhead, bringing Skyfield’s agreement with the Naval Observatory’s NOVAS library to within half a milliarcsecond.
  • The time method tt_calendar() method no longer raises a TypeError when its value is an array.
  • Running repr() on a Time array now produces a more compact string that only mentions the start and end of the time period.
  • The api.load() call no longer attempts to animate a progress bar if the user is running it under IDLE, which would try to accumulate the updates as a single long line that eventually hangs the window.

0.8

  • Added an api document to the project, in reverent imitation of the Pandas API Reference that I keep open in a browser tab every time I am using the Pandas library.
  • New method ICRF.separation_from() computes the angular separation between two positions.
  • Fixed == between Time objects and other unrelated objects so that it no longer raises an exception.

0.7

  • Introduced the Timescale object with methods utc(), tai(), tt(), and tdb() for building time objects, along with a load.timescale() method for building a new Timescale. The load method downloads ∆T and leap second data from official data sources and makes sure the files are kept up to date. This replaces all former techniques for building and specifying dates and times.

  • Renamed JulianDate to Time and switched from jd to t as the typical variable used for time in the documentation.

  • Deprecated timescale keyword arguments like utc=(…) for both the Time constructor and also for all methods that take time as an argument, including Body.at() and Topos.at().

  • Users who want to specify a target directory when downloading a file will now create their own loader object, instead of having to specify a special keyword argument for every download:

    load = api.Loader('~/ephemeris-files')
load('de421.bsp')

0.6.1

  • Users can now supply a target directory when downloading a file:

    load('de421.bsp', directory='~/ephemerides')

  • Fix: removed inadvertent dependency on the Pandas library.

  • Fix: load() was raising a PermissionError on Windows after a successful download when it tried to rename the new file.

0.6

  • Skyfield now generates its own estimate for delta_t if the user does not supply their own delta_t= keyword when specifying a date. This should make altitude and azimuth angles much more precise.
  • The leap-second table has been updated to include 2015 July 1.
  • Both ecliptic and galactic coordinates are now supported.

0.5

  • Skyfield has dropped the 16-megabyte JPL ephemeris DE421 as an install dependency, since users might choose another ephemeris, or might not need one at all. You now ask for a SPICE ephemeris to be downloaded at runtime with a call like planets = load('de421.bsp').

  • Planets are no longer offered as magic attributes, but are looked up through the square bracket operator. So instead of typing planets.mars you should now type planets['mars']. You can run print(planets) to learn which bodies an ephemeris supports.

  • Ask for planet positions with body.at(t) instead of body(t).

  • Per IAU 2012 Resolution B2, Skyfield now uses lowercase au for the astronomical unit, and defines it as exactly 149 597 870 700 meters. While this API change is awkward for existing users, I wanted to make the change while Skyfield is still pre-1.0. If this breaks a program that you already have running, please remember that a quick pip install skyfield==0.4 will get you up and running again until you have time to edit your code and turn AU into au.

0.4

0.3

  • The floating-point values of an angle a.radians, a.degrees, and a.hours are now attributes instead of method calls.