<p>Stellarium 0.14 or later has a checkbox under Configuration, Tools, Planetarium options:
Include <a href="https://en.wikipedia.org/wiki/Nutation" rel="nofollow">nutation</a>.
If I uncheck it, the RA and Dec of date for those stars on 2016/1/1
match yours within 0.2 arcsecond.</p>

<p>Some libraries distinguish between astrometric and apparent positions,
<a href="https://en.wikipedia.org/wiki/Aberration_of_light" rel="nofollow">aberration</a>
making up to 20 arcseconds difference.</p>

CC BY-SA 3.0
2016-08-17T20:08:50.987Z
2016-08-18T05:09:56.290Z
2016-08-18T05:09:56.290Z
Mike G
<p>I'm developing my own planetarium software and I using Stellarium to check if the values a get from my software are correct or not.</p>

<p>All values are roughly equal, being different only in the seconds.</p>

<p>These are Stellarium coordiantes followed by my coordinates.</p>

<p>Note, this is a CSV txt file. I don't know if I can attached to this question so I have pasted here:</p>

<pre><code>Star;RA J2000;DEC J2000;RA J2016;DEC J2016;Hour Angle;AZ;Alt.
Betelgeuse (Stellarium);5h55m10.34s;7d24m25.6s;5h56m2.38s;7d24m22.0s;23h52m25.55s;+176d38m27.3s;+55d59m52.0s
Betelgeuse (My software);5h55m10.34s;7d24m25.596s;5h56m2.32s;7d24m31.74s;23h52m25.6662s;+176d38m29.643s;+56d00m01.836s
Rigel (Stellarium);5h14m32.28s;-8d12m05.9s;5h15m18.50s;-8d11m12.8s;00h33m09.44s;+190d42m52.5s;+39d51m52.8s
Rigel (My software);5h14m32.279s;-8d12m05.9s;5h15m18.46s;-8d11m03.24s;00h33m09.5262s;+190d42m55.996s;+39d52m02.033s
Bellatrix (Stellarium);5h25m7.86s;+6d20m58.7s;5h25m59.49s;+6d21m37.1s;00h22m28.45s;+189d40m43.7s;+54d38m14.4s
Bellatrix (MySoftware);5h25m7.9s;+6d20m59s;5h25m59.42s;+6d21m46.71s;00h22m28.5662s;+189d40m48.830s;+54d38m23.685s
Mintaka (Stellarium);5h32m00.41s;-0d17m56.7s;5h32m49.55s;-0d17m27.8s;0h15m38.38s;+185d52m14.8s;+48d11m30.9s
Mintaka (MySoftware);5h32m00.42s;-0d17m56.6988s;05h32m49.51s;-0d17m18.1958s;00h15m38.4762s;+185d52m18.043s;+48d11m40.40s
Alnilam (Stellariumm);5h36m12.82s;-1d12m06.9s;5h37m01.63s;-1d11m44.00s;00h11m26.31s;+184d13m21.1s;+47d21m31.3s
Alnilam (My software);5h36m12.82s;-1d12m06.912s;5h37m01.57s;-1d11m34.2547s;00h11m26.4162s;+184d13m24.435s;+47d21m40.929s
Alnitak (Stellarium);5h40m45.54s;-1d56m33.2s;5h41m34.07s;-1d56m16.6s;00h06m53.87s;+182d30m42,7s;+46d40m01.3s
Alnitak (My software);5h40m45.55s;-1d56m33.2160s;5h41m34.03s;-1d56m06.8887;00h06m53.9562s;+182d30m45.212s;+46d40m10.931s
Saiph (Stellarium);5h47m45.40s;-9d40m10.6s;5h48m31.01s;-9d40m03.7s;23h59m56.93s;+179d59m01.5s;+38d57m56.3s
Saiph (My software);5h47m45.38s;-9d40m10.5960s;5h48m30.9500s;-9d39m54.0031s;23h59m57.0362s;+179d59m03.631s;+38d58m05.992s
</code></pre>

<p>Is that different a problem? </p>

<p>I don't know which value is the correct one (the one from Stellarium or the one from my software). The maximum difference is about 10 seconds.</p>

<p>And the difference between declinations (Stellarium and mine) is always greater that the difference between right ascensions.</p>

CC BY-SA 3.0
2016-01-09T19:40:21.667Z
This is possibly more a computing question than an astronomy question. Computer mathematics is (generally) only an approximation - hence errors creep in and over time these can grow. To avoid this you can use arbitrary precision integer libraries but you'll likely take a huge performance hit.
adrianmcmenamin
<star><coordinate>
Calculating AZ and ALT from RA and DEC: values are slightly different from Stellarium
VansFannel
# Calculating AZ and ALT from RA and DEC: values are slightly different from Stellarium

(Asked by: username_0 on 2016-01-09)

I'm developing my own planetarium software and I using Stellarium to check if the values a get from my software are correct or not.
All values are roughly equal, being different only in the seconds.
These are Stellarium coordiantes followed by my coordinates.
Note, this is a CSV txt file. I don't know if I can attached to this question so I have pasted here:
Star;RA J2000;DEC J2000;RA J2016;DEC J2016;Hour Angle;AZ;Alt.
Betelgeuse (Stellarium);5h55m10.34s;7d24m25.6s;5h56m2.38s;7d24m22.0s;23h52m25.55s;+176d38m27.3s;+55d59m52.0s
Betelgeuse (My software);5h55m10.34s;7d24m25.596s;5h56m2.32s;7d24m31.74s;23h52m25.6662s;+176d38m29.643s;+56d00m01.836s
Rigel (Stellarium);5h14m32.28s;-8d12m05.9s;5h15m18.50s;-8d11m12.8s;00h33m09.44s;+190d42m52.5s;+39d51m52.8s
Rigel (My software);5h14m32.279s;-8d12m05.9s;5h15m18.46s;-8d11m03.24s;00h33m09.5262s;+190d42m55.996s;+39d52m02.033s
Bellatrix (Stellarium);5h25m7.86s;+6d20m58.7s;5h25m59.49s;+6d21m37.1s;00h22m28.45s;+189d40m43.7s;+54d38m14.4s
Bellatrix (MySoftware);5h25m7.9s;+6d20m59s;5h25m59.42s;+6d21m46.71s;00h22m28.5662s;+189d40m48.830s;+54d38m23.685s
Mintaka (Stellarium);5h32m00.41s;-0d17m56.7s;5h32m49.55s;-0d17m27.8s;0h15m38.38s;+185d52m14.8s;+48d11m30.9s
Mintaka (MySoftware);5h32m00.42s;-0d17m56.6988s;05h32m49.51s;-0d17m18.1958s;00h15m38.4762s;+185d52m18.043s;+48d11m40.40s
Alnilam (Stellariumm);5h36m12.82s;-1d12m06.9s;5h37m01.63s;-1d11m44.00s;00h11m26.31s;+184d13m21.1s;+47d21m31.3s
Alnilam (My software);5h36m12.82s;-1d12m06.912s;5h37m01.57s;-1d11m34.2547s;00h11m26.4162s;+184d13m24.435s;+47d21m40.929s
Alnitak (Stellarium);5h40m45.54s;-1d56m33.2s;5h41m34.07s;-1d56m16.6s;00h06m53.87s;+182d30m42,7s;+46d40m01.3s
Alnitak (My software);5h40m45.55s;-1d56m33.2160s;5h41m34.03s;-1d56m06.8887;00h06m53.9562s;+182d30m45.212s;+46d40m10.931s
Saiph (Stellarium);5h47m45.40s;-9d40m10.6s;5h48m31.01s;-9d40m03.7s;23h59m56.93s;+179d59m01.5s;+38d57m56.3s
Saiph (My software);5h47m45.38s;-9d40m10.5960s;5h48m30.9500s;-9d39m54.0031s;23h59m57.0362s;+179d59m03.631s;+38d58m05.992s

Is that different a problem? 
I don't know which value is the correct one (the one from Stellarium or the one from my software). The maximum difference is about 10 seconds.
And the difference between declinations (Stellarium and mine) is always greater that the difference between right ascensions.

**Tags:** star, coordinate
> **Comments:**
> **username_1**: This is possibly more a computing question than an astronomy question. Computer mathematics is (generally) only an approximation - hence errors creep in and over time these can grow. To avoid this you can use arbitrary precision integer libraries but you'll likely take a huge performance hit.  

---

## 1 answers

### Answer by username_2 on 2016-08-17. Score: 2

Stellarium 0.14 or later has a checkbox under Configuration, Tools, Planetarium options:
Include [nutation](https://en.wikipedia.org/wiki/Nutation).
If I uncheck it, the RA and Dec of date for those stars on 2016/1/1
match yours within 0.2 arcsecond.

Some libraries distinguish between astrometric and apparent positions,
[aberration](https://en.wikipedia.org/wiki/Aberration_of_light)
making up to 20 arcseconds difference.


---

