Skyfield: Home • Table of Contents • Changelog • API Reference
The Skyfield API is build atop vector functions that take time as input and produce a position vector. You can create vector functions for the Earth, Moon, Sun, planets, and Earth satellites, and can combine them using addition and subtraction.
skyfield.vectorlib.
VectorFunction
¶Given a time, computes a corresponding position.
center
¶The Solar System object from which this vector is measured.
Often this is an integer code like 399
for the Earth,
3
for the center of gravity of the Earth-Moon system,
or 0
for the very center of the Solar System itself,
though it might also be a specific object
like a GeographicPosition
on the Earth’s surface
or an EarthSatellite
in orbit around it.
target
¶Using the same set of possible values as the center
,
this attribute names the target to which the vector is pointing.
The vector, then, is the three-dimensional difference
between the position of the center and that of the target.
vf1 + vf2
Return a new vector function whose at(t)
, when called,
computes the sum of the original vectors vf1
and vf2
.
This will raise an error
unless the target
where one of the two vectors ends
is the same as the center
from which the other vector starts.
vf1 - vf2
Return a new vector function whose at(t)
, when called,
computes where the target
of vf1
will be positioned
relative to the target
of the subtracted vf2
.
Note that this will be an instantaneous vector,
uncorrected for the amount of time light takes
to travel from one target to the other.
This raises an error
unless the two vectors share the same center
.
at
(t)¶At time t
, compute the target’s position relative to the center.
If t
is an array of times, then the returned position object
will specify as many positions as there were times. The kind of
position returned depends on the value of the center
attribute:
Barycentric
Geocentric
Geometric
ICRF