<p>This answer assumes that the observer's geographic latitude is 47.6&deg;N and their local sidereal time is 12<sup>h</sup>, putting their zenith at the coordinates in the headline.</p>

<p>Among the other five positions, the declinations are all within 8&deg; of +47.6&deg;, while the right ascensions are all over the place.
We can narrow the choices by comparing right ascensions to 12<sup>h</sup>:
the positions in Cygnus and Perseus are over 8<sup>h</sup> away,
and the position in Lynx is about 4<sup>h</sup> away,</p>

<p>The positions in Canes Venatici and Ursa Major are both within 1.5<sup>h</sup> of the target RA.
In this case we can get away with a rough approximation to the angular separation between positions <em>i</em> and <em>j</em>:
<span class="math-container">$$\theta_{ij} \approx \sqrt{\left(15 (\alpha_i - \alpha_j) \cos \frac{\delta_i + \delta_j}{2} \right)^2 + (\delta_i - \delta_j)^2}$$</span>
where <em>&alpha;</em> and <em>&delta;</em> are RA and Dec.</p>

<p>A precise solution would involve vector calculations similar to <a href="/a/19292">this answer</a>.</p>

CC BY-SA 4.0
2020-01-10T04:02:27.943Z
2020-01-10T04:16:06.300Z
2020-01-10T04:16:06.300Z
Mike G
<p>With Stellarium, it appears that the point with coordinates RA=12, DEC=47.6 is in Ursa Major.</p>

<p>In the screenshot from Stellarium below, the constellation boundaries are in red. Ursa Major is at the bottom, Canis is on top. The blue grid is the equatorial coordinates.</p>

<p><a href="https://i.sstatic.net/k51J4.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/k51J4.png" alt="Stellarium screenshot"></a></p>

CC BY-SA 4.0
2020-01-08T08:04:40.063Z
2020-01-08T08:04:40.063Z
usernumber
<p>I have several options, but I do not know how to calculate which option is closest to the zenith in title. Could you please help me with this? Thank you.</p>

<pre><code>Canes Venatici,CVN,13.14763.+40.04187,M
Cygnus,CYG,20.61006,+42.53633,A
Lynx,LYN,8.01440,+46.23233,M
Perseus,PER,3.49832,+43.88451,A
Ursa Major,UMA,10.98253,+52.52900,A
</code></pre>

CC BY-SA 4.0
2020-01-08T05:31:20.873Z
You might not have the question described correctly. According to http://djm.cc/constellation.html `12.00 +47.6` is in Ursa Major. I think if you provided geographic coordinates in latitude and longitude, *then you can ask* which constellation is closest to the zenith provided with the coordinates.  *If for example 47.6 were latitude*, then the zenith would have a declination of 90-47.6=42.2 degrees, and that seems closest to the declination given for Cygnus.
uhoh
CC BY-SA 4.0
2020-01-08T07:48:51.510Z
@uhoh If 47.6 is a latitude, don't you also need a time to know the declination of the zenith?
usernumber
CC BY-SA 4.0
2020-01-08T08:38:39.713Z
@usernumber Aha! yes indeed, you are way ahead of me! :-) but if it is a normal time, then you would need the time of year as well. However, if the 12 is a *sidereal time* then maybe it's good to go? See item #6 in https://astronomy.stackexchange.com/a/32621/7982
uhoh
<star><positional-astronomy>
What constellation is closest to the Zenith with RA=12 and Dec =47.6?
Boris
# What constellation is closest to the Zenith with RA=12 and Dec =47.6?

(Asked by: username_0 on 2020-01-08)

I have several options, but I do not know how to calculate which option is closest to the zenith in title. Could you please help me with this? Thank you.
Canes Venatici,CVN,13.14763.+40.04187,M
Cygnus,CYG,20.61006,+42.53633,A
Lynx,LYN,8.01440,+46.23233,M
Perseus,PER,3.49832,+43.88451,A
Ursa Major,UMA,10.98253,+52.52900,A

**Tags:** star, positional-astronomy

> **Comments:**
> **username_1**: You might not have the question described correctly. According to http://djm.cc/constellation.html `12.00 +47.6` is in Ursa Major. I think if you provided geographic coordinates in latitude and longitude, *then you can ask* which constellation is closest to the zenith provided with the coordinates.  *If for example 47.6 were latitude*, then the zenith would have a declination of 90-47.6=42.2 degrees, and that seems closest to the declination given for Cygnus.  
> **username_2**: @username_1 If 47.6 is a latitude, don't you also need a time to know the declination of the zenith?  
> **username_1**: @username_2 Aha! yes indeed, you are way ahead of me! :-) but if it is a normal time, then you would need the time of year as well. However, if the 12 is a *sidereal time* then maybe it's good to go? See item #6 in https://astronomy.stackexchange.com/a/32621/7982  

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## 2 answers

### Answer by username_3 on 2020-01-10. Score: 1

This answer assumes that the observer's geographic latitude is 47.6°N and their local sidereal time is 12h, putting their zenith at the coordinates in the headline.

Among the other five positions, the declinations are all within 8° of +47.6°, while the right ascensions are all over the place.
We can narrow the choices by comparing right ascensions to 12h:
the positions in Cygnus and Perseus are over 8h away,
and the position in Lynx is about 4h away,

The positions in Canes Venatici and Ursa Major are both within 1.5h of the target RA.
In this case we can get away with a rough approximation to the angular separation between positions *i* and *j*:
$$\theta\_{ij} \approx \sqrt{\left(15 (\alpha\_i - \alpha\_j) \cos \frac{\delta\_i + \delta\_j}{2} \right)^2 + (\delta\_i - \delta\_j)^2}$$
where *α* and *δ* are RA and Dec.

A precise solution would involve vector calculations similar to [this answer](/a/19292).


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### Answer by username_2 on 2020-01-08. Score: 1

With Stellarium, it appears that the point with coordinates RA=12, DEC=47.6 is in Ursa Major.

In the screenshot from Stellarium below, the constellation boundaries are in red. Ursa Major is at the bottom, Canis is on top. The blue grid is the equatorial coordinates.

[![Stellarium screenshot](https://i.sstatic.net/k51J4.png)](https://i.sstatic.net/k51J4.png)


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