<p>Does anyone know where the solar barycentre is in the old equatorial (based on Earth's position on midday, 01/01/2000) system? I want to add an ICRS option for a 3d model I'm working on.
EDIT: degrees would be ideal (0h = 0 degrees, 12h = 180), but RADEC works too.</p>

CC BY-SA 4.0
2023-07-15T05:14:16.590Z
Typical SSB (Solar System Barycentre) plots are relative to the Sun, eg https://astronomy.stackexchange.com/a/28036/16685 & https://astronomy.stackexchange.com/a/44903/16685 But Horizons will happily supply vectors for the SSB relative to Earth, if you want.
PM 2Ring
CC BY-SA 4.0
2023-07-15T05:34:53.133Z
Eg, https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&OUT_UNITS=KM-S&REF_PLANE=E&VEC_LABELS=NO&CSV_FORMAT=YES&OBJ_DATA=NO&VEC_TABLE=2&COMMAND=0&CENTER=%40399&START_TIME=%272000-Jan-1+12%3A00+UTC%27&STOP_TIME=2001-Jan-1&STEP_SIZE=1d That query uses the J2000.0 ecliptic plane as the XY plane. If you want the equatorial plane, set `REF_PLANE=F`, see https://ssd.jpl.nasa.gov/horizons/manual.html#frames for details.
PM 2Ring
CC BY-SA 4.0
2023-07-15T23:57:48.363Z
@PM2Ring Thank-you. Where can I enter REF_PLANE=F? I can't seem to find that option anywhere.
Kazon
CC BY-SA 4.0
2023-07-16T00:03:30.283Z
Like this: https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&OUT_UNITS=KM-S&REF_PLANE=F&VEC_LABELS=NO&CSV_FORMAT=YES&OBJ_DATA=NO&VEC_TABLE=2&COMMAND=0&CENTER=%40399&START_TIME=%272000-Jan-1+12%3A00+UTC%27&STOP_TIME=2001-Jan-1&STEP_SIZE=1d `F` is an abbreviation of `FRAME`. For more details on this API see https://ssd-api.jpl.nasa.gov/doc/horizons.html
PM 2Ring
CC BY-SA 4.0
2023-07-16T01:19:59.450Z
Sorry, I just noticed your edit. I see you want RA & DEC, which you get from an Observer Table. With that table, you don't specify a reference plane directly. The astrometric RA & DEC essentially use the J2000.0 ecliptic & equinox, the apparent RA & DEC use the instantaneous ecliptic & equinox of the requested date.
PM 2Ring
CC BY-SA 4.0
2023-07-16T06:10:57.900Z
The RA/Dec coordinates will change continuously due to Earth's motion around it.  It's apparent position can be computed the same as any other solar system object by using the coordinates 0,0,0.
Greg Miller
CC BY-SA 4.0
2023-07-16T06:49:55.883Z
@GregMiller Is the apparent position where it was during the J2K epoch?
Kazon
CC BY-SA 4.0
2023-07-16T08:47:15.550Z
@Kazon I don't understand what you want to do with this RA/DEC data. But anyway, here it is for J2000.0 (and a few days following), using the file API.
PM 2Ring
CC BY-SA 4.0
2023-07-16T08:47:27.843Z
https://sagecell.sagemath.org/?z=eJxlUVtr2zAUfjf4P2hZQQm4iuKulAYEVWIl0VZfKqmF9EWYxW1dEtuzlTFa-t93bLK-7EVwvpuk831Fm7ot3-qqQ7viUBOUxShUZfWMQhpeEBoSeuV75aGpW4fa4tex6FyHfM_3ju0eMTR6ca7p5tNp1-3Ia7MnVd7l5Ln-Pc2bcvpyyrZP5b4ggIwG68_DrreORr735exMpyvfi_kPYUW2ETHbCu17yzSOeRIx6nsDas02EyxdaKEehAJeJEYohi8pvbm4vsa-pw1XxhoZC4ZDSun5a16dz9AsnFOKjBkUafafgA6EyKyWj0DMUMS3GrC7e54YaaTQAAZh8O0SQCVWVm9BHjMsl2oF0JLf2lWqYm4YXqRmc4KG5-I1TP2FNpJraSAplsm9EX0-T9afvkj0Qp5lXMG3GOZS3Qrdq5b64VOVpACki-824oafRtjhsFFoBjb6rx_S1J0bQ0EB2uUuZ-_4qW4PucNzhF3xx-GPAPWNdMCUVXPsiTGGVnCA4Jx8THyvacvKjSGR9I7JX-dqlpw=&lang=python
PM 2Ring
CC BY-SA 4.0
2023-07-16T16:38:33.370Z
@Kazon, the apparent position changes every day, just like it does for the Sun.
Greg Miller
<coordinate-systems>
Equatorial Co-Ordinates of the Solar Barycentre
Kazon
# Equatorial Co-Ordinates of the Solar Barycentre

(Asked by: username_0 on 2023-07-15)

Does anyone know where the solar barycentre is in the old equatorial (based on Earth's position on midday, 01/01/2000) system? I want to add an ICRS option for a 3d model I'm working on.
EDIT: degrees would be ideal (0h = 0 degrees, 12h = 180), but RADEC works too.

**Tags:** coordinate-systems

> **Comments:**
> **username_1**: Typical SSB (Solar System Barycentre) plots are relative to the Sun, eg https://astronomy.stackexchange.com/a/28036/16685 & https://astronomy.stackexchange.com/a/44903/16685 But Horizons will happily supply vectors for the SSB relative to Earth, if you want.  
> **username_1**: Eg, https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&OUT_UNITS=KM-S&REF_PLANE=E&VEC_LABELS=NO&CSV_FORMAT=YES&OBJ_DATA=NO&VEC_TABLE=2&COMMAND=0&CENTER=%40399&START_TIME=%272000-Jan-1+12%3A00+UTC%27&STOP_TIME=2001-Jan-1&STEP_SIZE=1d That query uses the J2000.0 ecliptic plane as the XY plane. If you want the equatorial plane, set `REF_PLANE=F`, see https://ssd.jpl.nasa.gov/horizons/manual.html#frames for details.  
> **username_0**: @PM2Ring Thank-you. Where can I enter REF_PLANE=F? I can't seem to find that option anywhere.  
> **username_1**: Like this: https://ssd.jpl.nasa.gov/api/horizons.api?format=text&EPHEM_TYPE=V&OUT_UNITS=KM-S&REF_PLANE=F&VEC_LABELS=NO&CSV_FORMAT=YES&OBJ_DATA=NO&VEC_TABLE=2&COMMAND=0&CENTER=%40399&START_TIME=%272000-Jan-1+12%3A00+UTC%27&STOP_TIME=2001-Jan-1&STEP_SIZE=1d `F` is an abbreviation of `FRAME`. For more details on this API see https://ssd-api.jpl.nasa.gov/doc/horizons.html  
> **username_1**: Sorry, I just noticed your edit. I see you want RA & DEC, which you get from an Observer Table. With that table, you don't specify a reference plane directly. The astrometric RA & DEC essentially use the J2000.0 ecliptic & equinox, the apparent RA & DEC use the instantaneous ecliptic & equinox of the requested date.  
> **username_2**: The RA/Dec coordinates will change continuously due to Earth's motion around it.  It's apparent position can be computed the same as any other solar system object by using the coordinates 0,0,0.  
> **username_0**: @GregMiller Is the apparent position where it was during the J2K epoch?  
> **username_1**: @username_0 I don't understand what you want to do with this RA/DEC data. But anyway, here it is for J2000.0 (and a few days following), using the file API.  
> **username_1**: https://sagecell.sagemath.org/?z=eJxlUVtr2zAUfjf4P2hZQQm4iuKulAYEVWIl0VZfKqmF9EWYxW1dEtuzlTFa-t93bLK-7EVwvpuk831Fm7ot3-qqQ7viUBOUxShUZfWMQhpeEBoSeuV75aGpW4fa4tex6FyHfM_3ju0eMTR6ca7p5tNp1-3Ia7MnVd7l5Ln-Pc2bcvpyyrZP5b4ggIwG68_DrreORr735exMpyvfi_kPYUW2ETHbCu17yzSOeRIx6nsDas02EyxdaKEehAJeJEYohi8pvbm4vsa-pw1XxhoZC4ZDSun5a16dz9AsnFOKjBkUafafgA6EyKyWj0DMUMS3GrC7e54YaaTQAAZh8O0SQCVWVm9BHjMsl2oF0JLf2lWqYm4YXqRmc4KG5-I1TP2FNpJraSAplsm9EX0-T9afvkj0Qp5lXMG3GOZS3Qrdq5b64VOVpACki-824oafRtjhsFFoBjb6rx_S1J0bQ0EB2uUuZ-_4qW4PucNzhF3xx-GPAPWNdMCUVXPsiTGGVnCA4Jx8THyvacvKjSGR9I7JX-dqlpw=&lang=python  
> **username_2**: @username_0, the apparent position changes every day, just like it does for the Sun.  

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## 0 answers

