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Define ECT in documentation.

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Define ECT = True Ecliptic of Date in the documentation.
I will soon convert the Ecliptic() functions to return ECT instead of
ECL, but I will retain ECL support via rotation matrix functions.
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Don Cross
2022-12-06 13:36:47 -05:00
parent 12e68a1931
commit 742ab4cbff
10 changed files with 40 additions and 30 deletions
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source/python/README.md
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@@ -135,15 +135,16 @@ To get started quickly, here are some [examples](../../demo/python/).
### Coordinate transforms
The following five orientation systems are supported.
The following orientation systems are supported.
Astronomy Engine can convert a vector from any of these orientations to any of the others.
It also allows converting from a vector to spherical (angular) coordinates and back,
within a given orientation. Note the 3-letter codes for each of the orientation systems;
these are used in function and type names.
- **EQJ = Equatorial J2000**: Uses the Earth's equator on January 1, 2000, at noon UTC.
- **EQD = Equator of-date**: Uses the Earth's equator on a given date and time, adjusted for precession and nutation.
- **ECL = Ecliptic**: Uses the mean plane of the Earth's orbit around the Sun. The x-axis is referenced against the J2000 equinox.
- **EQD = Equator of Date**: Uses the Earth's equator on a given date and time, adjusted for precession and nutation.
- **ECT = True Ecliptic of Date**: Uses the true orbital plane and equator of the Earth on the given date.
- **ECL = Mean J2000 Ecliptic**: Uses the plane of the Earth's orbit around the Sun in the year 2000. The x-axis is referenced against the J2000 mean equinox.
- **HOR = Horizontal**: Uses the viewpoint of an observer at a specific location on the Earth at a given date and time.
- **GAL = Galactic**: Based on the IAU 1958 definition of galactic coordinates.