<p>1 hour = 15 degrees.  60 min = 1 hour and 60×60=3600 sec = 1hour.</p>
<p>So to convert: <code>(5 + 38/60 + 42.0/3600)*15</code> = 84.675</p>
<p>There is a small discrepancy, which is due to the fact that your quoted value is the simbad location of the sigma ori <em>cluster</em>, and not the bright central star, which is at  05 38 44.76538 according to simbad and identical to the Gaia value, as calculated below.</p>
<p>Reverse the process:</p>
<p><code>84.68652242854718 / 15</code> = 5.6457681619</p>
<p><code>0.6457681619 * 60</code> = 38.746089714</p>
<p><code>0.746089714 * 60</code> = 44.76538284</p>
<p>so 84.68652242854718 = 05h 38m 44.8s</p>

CC BY-SA 4.0
2022-09-11T19:31:15.710Z
Actually the descrepacy is probably due to the fact that sigma ori is not a point star, but a tight cluster with multiple sources very close to each other.  Simbad gives the ra of the main star as 05 38 44.76538  and the ra of the cluster as 05 38 44.0
James K
CC BY-SA 4.0
2022-09-12T05:36:40.173Z
Thank you so much.
Elena Greg
CC BY-SA 4.0
2022-09-12T11:52:37.383Z
I never understood the advantage of using hh:mm:ss instead of degrees. Do astronomers really find hh:mm:ss more convenient?
Eric Duminil
CC BY-SA 4.0
2022-09-12T12:28:10.030Z
@EricDuminil Some of them apparently (still) do. I do not. I guess in the days of computer processing it is just a relic of the past, much like using sexagesimal angles DDD°mm'ss" instead of plain decimal degrees.
Martin 'Kvík' Baláž
CC BY-SA 4.0
2022-09-12T12:56:32.097Z
I have vague recollections of having to do time based math to use the setting circles on an old telescope in a class I took about 20 years ago.
Dan Is Fiddling By Firelight
CC BY-SA 4.0
2022-09-11T19:14:41.793Z
2022-09-11T20:26:28.003Z
2022-09-11T20:26:28.003Z
James K
<p>What is the difference between Right ascension in Simbad and Gaia Archive, please? How to convert the values? For instance, HD 37468: 05h 38m 42.0s vs 84.68652242854718 deg. Should not be these values nearly the same? How to convert in astropy, please?</p>

<coordinate><astropy>
Right ascension - Gaia vs Simbad
Elena Greg
# Right ascension - Gaia vs Simbad

(Asked by: username_0 on 2022-09-11)

What is the difference between Right ascension in Simbad and Gaia Archive, please? How to convert the values? For instance, HD 37468: 05h 38m 42.0s vs 84.68652242854718 deg. Should not be these values nearly the same? How to convert in astropy, please?

**Tags:** coordinate, astropy


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## 1 answers

### Answer by username_1 on 2022-09-11. Score: 8 | Accepted answer

1 hour = 15 degrees. 60 min = 1 hour and 60×60=3600 sec = 1hour.

So to convert: `(5 + 38/60 + 42.0/3600)*15` = 84.675

There is a small discrepancy, which is due to the fact that your quoted value is the simbad location of the sigma ori *cluster*, and not the bright central star, which is at 05 38 44.76538 according to simbad and identical to the Gaia value, as calculated below.

Reverse the process:

`84.68652242854718 / 15` = 5.6457681619

`0.6457681619 * 60` = 38.746089714

`0.746089714 * 60` = 44.76538284

so 84.68652242854718 = 05h 38m 44.8s

> **Comments:**
> **username_1**: Actually the descrepacy is probably due to the fact that sigma ori is not a point star, but a tight cluster with multiple sources very close to each other.  Simbad gives the ra of the main star as 05 38 44.76538  and the ra of the cluster as 05 38 44.0  
> **username_0**: Thank you so much.  
> **username_2**: I never understood the advantage of using hh:mm:ss instead of degrees. Do astronomers really find hh:mm:ss more convenient?  
> **username_3**: @EricDuminil Some of them apparently (still) do. I do not. I guess in the days of computer processing it is just a relic of the past, much like using sexagesimal angles DDD°mm'ss" instead of plain decimal degrees.  
> **username_4**: I have vague recollections of having to do time based math to use the setting circles on an old telescope in a class I took about 20 years ago.  

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