<p>When asking Horizons for ephemeris, it doesn't include the information of the rotation axis. Is there a way to obtain it?(may include calculations based on the given information)</p>
<p>And is there any way to get the rotation status (the angular distance of the prime meridian to the ascending node)? Thanks</p>
<p>I would like a more precise data(taking perturbation over time into account) then the <a href="https://en.wikipedia.org/wiki/Axial_tilt" rel="nofollow noreferrer">The wikipedia page</a></p>

CC BY-SA 4.0
2024-07-16T11:52:24.727Z
I don't believe Horizons will compute those, but this text SPICE kernel has the information needed to compute it for many solar system bodies. https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00011.tpc
Greg Miller
CC BY-SA 4.0
2024-07-16T14:18:00.510Z
See 32. Target north-pole RA & DEC https://ssd.jpl.nasa.gov/horizons/manual.html#obsquan
PM 2Ring
CC BY-SA 4.0
2024-07-18T03:46:41.600Z
@PM2Ring Thanks a lot! But the data is taking light-time aberration into account. It there a way to show the "real" state at the specific time?
And it shows Earth's DEC is nearly 90 degrees. Does that mean it uses Earth's equatorial plane at J2000 as the x-y plane?
Stellar Horizon
CC BY-SA 4.0
2024-07-18T05:41:51.877Z
@StellarHorizon The manual says "RA & DEC are consistent with the requested reference frame (ICRF or FK4/B1950)". So the Earth's north celestial pole has declination = ~90° in the ICRF frame, which is very closely aligned to the J2000 frame (within a few milliarcsecs). SPICE / Horizons uses very good Earth orientation data from the IERS.   The orientations of most other bodies are computed using (relatively) simple equations, as mentioned in the PCK file that Greg linked. The Moon uses a more sophisticated model.
PM 2Ring
CC BY-SA 4.0
2024-07-18T06:14:56.907Z
You can also ask Horizons for the vector from a body centre to the body's north pole. Here's an example for Mars: https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&REF_PLANE=F&VEC_TABLE=1&OUT_UNITS=KM-S&CSV_FORMAT=NO&OBJ_DATA=NO&COMMAND=%27g%3A0%2C90%2C0%40499%27&CENTER=%40499&START_TIME=2024-Jul-1&STOP_TIME=2024-Jul-2&STEP_SIZE=2h
PM 2Ring
<planet><coordinate><jpl-horizons>
How to get the direction of the rotation axis of a celestial body using JPL Horizons?
Stellar Horizon
# How to get the direction of the rotation axis of a celestial body using JPL Horizons?

(Asked by: username_0 on 2024-07-16)

When asking Horizons for ephemeris, it doesn't include the information of the rotation axis. Is there a way to obtain it?(may include calculations based on the given information)

And is there any way to get the rotation status (the angular distance of the prime meridian to the ascending node)? Thanks

I would like a more precise data(taking perturbation over time into account) then the [The wikipedia page](https://en.wikipedia.org/wiki/Axial_tilt)

**Tags:** planet, coordinate, jpl-horizons
> **Comments:**
> **username_1**: I don't believe Horizons will compute those, but this text SPICE kernel has the information needed to compute it for many solar system bodies. https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/pck00011.tpc  
> **username_2**: See 32. Target north-pole RA & DEC https://ssd.jpl.nasa.gov/horizons/manual.html#obsquan  
> **username_0**: @PM2Ring Thanks a lot! But the data is taking light-time aberration into account. It there a way to show the "real" state at the specific time? And it shows Earth's DEC is nearly 90 degrees. Does that mean it uses Earth's equatorial plane at J2000 as the x-y plane?  
> **username_2**: @StellarHorizon The manual says "RA & DEC are consistent with the requested reference frame (ICRF or FK4/B1950)". So the Earth's north celestial pole has declination = ~90° in the ICRF frame, which is very closely aligned to the J2000 frame (within a few milliarcsecs). SPICE / Horizons uses very good Earth orientation data from the IERS.   The orientations of most other bodies are computed using (relatively) simple equations, as mentioned in the PCK file that Greg linked. The Moon uses a more sophisticated model.  
> **username_2**: You can also ask Horizons for the vector from a body centre to the body's north pole. Here's an example for Mars: https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&REF_PLANE=F&VEC_TABLE=1&OUT_UNITS=KM-S&CSV_FORMAT=NO&OBJ_DATA=NO&COMMAND=%27g%3A0%2C90%2C0%40499%27&CENTER=%40499&START_TIME=2024-Jul-1&STOP_TIME=2024-Jul-2&STEP_SIZE=2h  

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## 0 answers

