Skyfield: Home • Table of Contents • Changelog • API Reference
Skyfield has only a single binary dependency, the NumPy vector library, and is designed to install cleanly with a single invocation of the standard Python package tool:
pip install skyfield
This should install Skyfield, NumPy,
and the small collection of pure-Python astronomy libraries
that Skyfield depends on.
If you lack pip
and need to install each dependency by hand,
consult Skyfield’s setup.py
file for the full list.
If trying to install Skyfield gives you errors about NumPy, there are several other ways to get NumPy installed:
It is best to simply use a science-ready version of Python that comes with NumPy built-in, like the Anaconda distribution.
You can download and run an official NumPy installer.
You can try to get the plain pip
-powered install working
by giving your system a functioning C compiler
that matches the compiler used to build Python.
On Windows with Python 2.7, try installing the free
Visual Studio Express 2008.
Mac users should install the “Xcode Command Line Tools”
to give pip
the superpower of being able to build and install
binary Python dependencies like NumPy.
Read the Changelog below to learn about recent fixes, changes,
and improvements to Skyfield.
You can protect your project from any abrupt API changes
by pinning a specific version of Skyfield
in your requirements.txt
or setup.py
or install instructions:
skyfield==1.34
By preventing Skyfield from getting accidentally upgraded until you are ready to advance the version number yourself, you can avoid even slight changes in behavior and output coordinates that might result from an upgrade. If you find any problems or would like to suggest an improvement, simply create an issue on the project’s GitHub page:
Good luck!
The Skyfield package offers a VERSION
tuple
that your code can use to test which version of Skyfield is running.
For example,
this code checks whether Skyfield is at least at version 1.24:
import skyfield
if skyfield.VERSION < (1, 24):
print('Too old')
A new featured added in Skyfield 1.36 (released January 2021)
is that you can invoke the skyfield
module from the command line
to display its version:
$ python -m skyfield
Skyfield version: 1.37
jplephem version: 2.14
sgp4 version: 2.17
Built-in leap seconds table ends with leap second at: 2016-12-31 23:59:60 UTC
Built-in ∆T table from finals2000A.all covers: 1973-01-01 to 2022-01-29
Also displayed are the versions of the libraries Skyfield depends on, and the start and end dates of its built-in timescale tables.
If Skyfield has proven useful in your research, the project welcomes your citation to bring it to the attention of other academics who might benefit from it.
ASCL: ascl:1907.024
Bibcode: 2019ascl.soft07024R
Current CITATION.cff file on GitHub: CITATION.cff
Permanent URL, used by several papers to uniquely identify Skyfield
(and which is by now a redirect to https:
but remains http:
in this URL to match papers already using it as an identifier):
http://rhodesmill.org/skyfield/
Times now support the <
operator, so Python can sort them.
For convenience, geoids like wgs84
have a
new attribute 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.
Added faster and more accurate rising and setting routines!
See Risings and settings for documentation and examples of the new
find_risings()
and
find_settings()
and
find_transits()
functions.
#662
Skyfield’s internal table for the ∆T Earth orientation parameter has been updated, so that its predictions now extend to 2025-01-18.
Constellation abbreviations are now consistent between the
load_constellation_map()
table and the
load_constellation_names()
list. Previously,
CVn
and TrA
had been mis-capitalized in the list as Cvn
and Tra
.
#906
The 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 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 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 Astrometric
position
subclass — which previously lacked the method — then a friendly
exception is raised explaining their error.
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.
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
.
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!
Fixed planetary_magnitude()
so it works
for Saturn even when the time is an array rather than a single time;
also, improved its calculation slightly with respect to Uranus.
#739
Improved load_comets_dataframe()
so that
parsing CometEls.txt
with the most recent version of Pandas
doesn’t stumble over the commas in the final field of (for example)
Halley’s Comet and give the error ParserError: Error tokenizing
data. C error: Expected 12 fields…saw 13
.
#707
Added two new position methods
phase_angle()
and
fraction_illuminated()
that, given an illuminator (usually the Sun) as their argument,
compute whether the observer is looking at the bright side or the dark
side of the target body.
They replace a pair of old functions in the almanac module.
The almanac routine moon_nodes()
would
sometimes skip nodes that were closer together than 14.0 days. It has
been tightened down and should now detect all lunar nodes.
#662
Time objects now feature a to_astropy()
method.
The position method to_skycoord()
now
sets the frame
attribute of the sky coordinate it returns, and for
now only supports barycentric and geocentric positions.
#577
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 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
Extended the planetary_magnitude()
routine to work with all the major planets, which upgrades it from a
prototype feature to a production feature of Skyfield.
The subpoint()
method has been
deprecated, because users reported that its name was a poor match for
its behavior. Four new methods have replaced it:
latlon_of()
,
height_of()
,
geographic_position_of()
, and
subpoint_of()
.
#644
Added a timescale method linspace()
.
#617
The 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
Angle.dstr()
and
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
The prototype 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 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 TEME
reference frame
used by SGP4 Earth satellite elements.
Added a 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
The Time
tuple utc
and method 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
Vector subtraction now returns the position subclass specific to the resulting vector’s center. #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
Added an 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
Angle.dstr()
and
Angle.hstr()
to return an array of strings when the angle itself is an array.
#527
Deprecated the old Topos
class,
which not only featured a clunky interface
but hid from users the fact that Skyfield was generating IERS2010 positions
from latitude and longitude
when in fact nearly all users want WGS84 positions.
Users are now encouraged to supply latitude and longitude
to the latlon()
method
of either the wgs84
object
or the iers2010
object.
Related discussion:
#372
The two new geoid objects wgs84
and iers2010
have also provided a happy new home
for the subpoint()
method —
which was previously stranded
over on the Geocentric
class,
where it couldn’t be used with positions of other classes
that might be centered at the geocenter.
(The old method will remain in place to support legacy code,
but is discouraged in new applications.)
The effects of Precession and Nutation — if configured — are now included both when computing the position in space of an Earth latitude and longitude, and when determining the latitude and longitude beneath a celestial position.
Added load_constellation_names()
.
The utc_jpl()
method now correctly
designates its return value as UTC
instead of the ambiguious UT
.
#515
The position classes have gained methods
frame_xyz()
,
frame_xyz_and_velocity()
,
frame_latlon()
, and
from_time_and_frame_vectors()
that work with a new library skyfield.framelib
to offer a number of familiar reference frames.
These replace the existing ad-hoc position methods
for ecliptic and galactic coordinates,
which are now deprecated (but will continue to be supported).
See Coordinates in other reference frames.
#476
Added an official itrs
reference frame.
Added support for IERS Precession and Nutation 𝑥 and 𝑦.
Added a method lst_hours_at()
that computes Local Sidereal Time.
A new almanac routine moon_phase()
returns
the Moon phase as an angle where 0° is New Moon, 90° is First Quarter,
180° is Full, and 270° is Last Quarter.
#282
Almanac search routines that previously returned a Boolean true/false
array now return an integer 0/1 array instead, to work around a new
deprecation warning in NumPy which, for example, would have outlawed
using the Boolean array from moon_nodes()
to
index into the MOON_NODES
list that provides a name for each node.
#486
The undocumented columns magnitude_H
and magnitude_G
in the
Minor Planet Center comets dataframe have been renamed magnitude_g
and magnitude_k
following further research on the file format
(which does not itself document which magnitude model is intended).
#416
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
A new lunar_eclipses()
routine finds
lunar eclipses and determines their degree of totality.
#445
The almanac module’s new meridian_transits()
routine can find the moments at which a body transits the meridian and
antimeridian.
#460
Fix: the find_minima()
function was
ignoring its epsilon
and num
arguments and always using the
default values instead.
#475
Fix: the .epoch
attribute of Earth satellite objects that were
built using from_satrec()
was, alas, a half-day off.
#466
Fix: the Topos
constructor arguments x
and y
,
which never worked properly anyway,
have been deprecated and are now ignored.
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 UT1 and downloading IERS data.
#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 days_old()
and
download()
make it simple to download a
fresh copy of a file if the copy on disk is older than you would like.
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 Time
object, if manually instantiated
without a Julian date fraction, now provides a fraction array with
dimensions that match the Julian date argument.
#458
Fix: the new Julian calendar feature was raising an exception in the
calendar methods like tt_calendar()
if
the time object was in fact an array of times.
#450
Fix: trying to iterate over a time object would raise an exception if
the time was created through ut1()
.
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 Timescale()
and 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 Ancient and modern dates
if you want to turn on Julian dates in your application.
#450
The printed appearance of both vectors and of vector functions like Earth locations and Earth satellites have been rewritten to be more informative and consistent.
Added compute_calendar_date()
which lets the
caller choose the Julian calendar for ancient dates instead of always
using the proleptic Gregorian calendar. This should be particularly
useful for historians.
Added J()
that builds a time array
from an array of floating point years.
#436
Added four new strftime
methods for the non-UTC timescales
(#443).
All four of them support %f
for microseconds,
and provide a reasonable default format string
for callers who don’t wish to concoct their own:
Thanks to several fixes, comets and asteroids with parabolic and hyperbolic orbits should now raise fewer errors.
The prototype planetary_magnitude()
can
now return magnitudes for Uranus without raising an exception. The
routine does not yet take into account whether the observer is facing
the equator or poles of Uranus, so the magnitude predicted for the
planet will only be accurate to within about 0.1 magnitudes.
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 timescale()
is called
(unless the builtin=True
parameter is provided). To make Skyfield
less fragile going forward:
The loader’s 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
.
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 UT1 and downloading IERS data
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 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
Added parse_constellations()
and parse_star_names()
to load Stellarium star names and constellation lines.
Constellation lines are featured in a new example script
Drawing a finder chart for comet NEOWISE that produces a finder chart
for comet C/2020 F3 NEOWISE.
The Hipparcos star catalog should now load faster, having switched behind the scenes to a higher performance Pandas import routine.
Fixed the ability of utc()
to
accept a Python datetime.date
object as its argument.
#409
Slightly lowered the precision of two tests when they detect that Python is compiled for a 32-bit processor, so the test suite can succeed when contributors package Skyfield for 32-bit Linux. #411
Added methods from_datetime()
and
from_datetimes()
to the
Timescale
class, to better advertise the
ability to build a Skyfield time from a Python datetime
— an ability
that was previously overloaded into the year
parameter of the
utc()
method (where it is still
supported for backwards compatibility, but no longer documented).
Fix: improved the accuracy with which velocity is converted between the Earth-fixed ITRF frame that rotates with the Earth and the inertial GCRS frame that does not. In particular, this should make Earth satellite velocities more accurate.
Added Kepler Orbits support for generating the positions of comets and asteroids from Minor Planet Center data files.
Added 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 Searching for the dates of astronomical events to match.
Made the 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.
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.
Searching for the dates of astronomical events is now documented for custom events that users define themselves, instead of only being documented for the official pre-written Almanac Computation 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 Time
array.
It is now possible to Build a satellite with a specific gravity model thanks to a new Earth satellite constructor method. #384
Added build_url()
that returns the URL
from which Skyfield will download a file.
#382
Added 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
Added 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 position_of_radec()
to replace the poorly designed position_from_radec()
.
Skyfield Time
objects now have microsecond
internal accuracy, so round trips to and from Python datetimes should
now preserve all the microsecond digits.
The 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
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
build_latlon_degrees()
.
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 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
Deprecated the old hybrid-key satellite dictionary returned by
load.tle()
in favor of a simple list returned by the new
tle_file()
routine.
#345
The almanac find_discrete()
routine no
longer returns extraneous values in its second return value if no
changes of state were found.
#339
#351
Added documentation and support for computing lunar libration. #80
Upgraded to a new version of the sgp4
Python library that, when
possible, uses the fast official C++ implementation of SGP4.
Added a find_events()
Earth
satellite method that finds the times at which a satellite rises,
culminates, and sets.
Improved the logic behind the Almanac Computation 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 utc_strftime()
method so it
does not report that every day in all of recorded history is a Monday.
#335
Added basic Planetary Reference Frames support, enough to compute the position of a given latitude and longitude on the surface of the Moon. #79 #124 #258
Added oppositions_conjunctions()
for finding
the dates when a planet is at opposition and conjunction with the sun.
Added position_angle_of()
for computing
astronomical position angles.
Changed the URL for the Hipparcos catalog, because the VizieR archives FTP server is no longer responding. #301
Added a dark_twilight_day()
function that
not only handles sunrise and sunset but also all three kinds of
twilight.
#225
Changed the URL from which leap second files are downloaded; the server that previously provided them is no longer responding. Thanks to Richard Shaw for the pull request. #296 #297
Added a risings_and_settings()
function for
computing rising and setting times.
#271
Provided a constellation lookup routine through
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
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.
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: find_discrete()
was generating empty
arrays of search dates, upsetting the astronomy code, if the start and
end dates were very close together.
#240
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
Added seasons()
to the Almanac Computation module
that can be used to predict solstices and equinoxes.
Fix: the ecliptic coordinate routines no longer raise ValueError:
too many values to unpack
if they are passed a time array.
#207
#208
There is now an Almanac Computation module that can compute the times of sunrise, sunset, and the phases of the moon, based on the search algorithms announced at my recent PyBay talk “An Import Loop and a Fiery Reentry.”
Two new methods cirs_xyz()
and
cirs_radec()
have been contributed
which provide support for rotating a position into the Celestial
Intermediate Reference System (CIRS).
#192
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 Stars and Distant Objects 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
osculating_elements_of()
.
A couple of bugs in the load()
routine have been fixed.
#193
#194
Both of the loader methods 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()
.
The subpoint()
method
now normalizes the longitude values it returns
into the range −180° to 180°
#182
and returns an actual elevation instead of zero.
#185
Earth satellites now return a real velocity vector instead of zero. #187
Earth satellites now offer an
ITRF_position_velocity_error()
method that returns raw ITRF coordinates for users interested in them.
#85
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
Geocentric coordinates now have a
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 Star
to be initialized with a tuple that breaks units into minutes and seconds
(broke in version 1.2).
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!)
Positions can now be converted to AstroPy with
to_skycoord()
.
You can now provide a timescale of your own to an
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.
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.
Added an API Reference 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.
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')
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.
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.
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.
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
.
To prevent confusion, the astimezone()
and utc_datetime()
methods
have been changed to return only a datetime
object.
If you also need a leap second flag returned,
call the new methods
astimezone_and_leap_second()
and utc_datetime_and_leap_second()
.
The floating-point values of an angle
a.radians
, a.degrees
, and a.hours
are now attributes instead of method calls.