### Find constellation over Earth coordinates on a specific date-time

• I would like some help in finding the exact constellations, or some sort of visualization of the stars over an specific location an time. The idea is to find out the closest star or group of stars on the vertical of that position in that exact moment.

I'm also aware than "vertical" can have some different interpretations, but a nice approximation should be good enough.

I'm not an expert in physics nor astronomy, but I think providing the coordinates and the date/time should be enough for an approximation.
According to google maps, the coordinates are:

39.467062 -0.377381

No idea what format that is, I'm familiarized with degree/minutes/seconds but I don't know exactly how to translate those. The time would be:

March 25, 2015, 09:40 (Spain)

, which would be 08:40 in UTC, correct me if I'm wrong.

Any help would be appreciated, if you can't provide a direct answer, at least point me to some website form or program (Linux preferably) I can use to find this out.

In case someone is wandering, this involves a girl and a tattoo, so please bear in mind this is something I'm going to be carrying for the rest of my life :)

Thanks!

Have you used stellarium, xephem, or a similar program?

As a matter of fact, yes, I found stellarium last night in the Ubuntu repos and I think I got it, beautifull program! I will answer my own question later when I have some spare time and would love to have some opinions because I would like to triple check this. Thanks!

• Ahh got it. The coordinates are given as latitude, longitude.

Fortunately, the longitude hardly matters (depending what precision you need), but the latitude does. A star at the zenith will have a declination equal to the latitude on Earth.

As far as Right Ascension goes, well around the March equinox then stars with 12 hours in Right Ascension will reach their highest point (culmination) at "local midnight".

So one would expect roughly speaking for stars at around 21 hours, +40 would be overhead at 9h40m later.

Checking out Stellarium for that location and time it seems that this is pretty much spot on and that Cygnus (the Swan) is overhead, with the bright star Deneb very close to being at Zenith.

Ok, that's what I thought, but my knowledge of astronomy is pretty basic, high-school level. Thanks for the confirmation! I don't expect use this forum much (I'm much more active on askubuntu) so I'll wait until I can start a bounty and give you my points.

• There's a couple of celestial coordinate systems you should learn about, which are the most commonly used:

1. Horizontal coordinate system, observer-centered.

2. Equatorial coordinate system, earth-centered.

Depending on the system you use, the coordinates of your celestial object will be represented in one way or the other and should be read accordingly.

I see, I know the celestial coordinate systems are far more complex than I can grasp... but would this really affect the vertical of the Earth coordinates? I mean, after all, in that instant there was a constellation over that place and that's that... Also, as I said, precision is not a big deal. Thanks for your input!