<p>What I do is compute the limiting magnitude for the position of the object I am interested in, and subtract it from the magnitude of the object (I call this the magnitude contrast).  If negative, it should be visible with the naked eye.  I use the function limmag_jd() in the Fortran library <a href="http://libthesky.sourceforge.net" rel="nofollow">libTheSky</a> for this.</p>

<p>In order to find the best moment in a given night, I compute the contrast for say every 15 minutes, and find the minimum.  You can do this for a number of nights, until the best contrast found is negative, which would be the heliacal rising.</p>

<p>I'm not sure whether there is an easy way using a simple equation - the limiting magnitude will depend on things like the positions of Sun, Moon and the object in question, the phase of the Moon, the magnitude of the object, etc.</p>

CC BY-SA 3.0
2015-11-28T13:57:35.347Z
2015-11-28T13:57:35.347Z
AstroFloyd
<p>I imagine there are several possible conditions for determining the time of a helical rising of a star, the elevation of the star at sunrise, the latitude of the observer, and the azimuth of the star. </p>

<p>Is there any kind of equation (or plot/graphic) that relates these variables and can be used to predict whether a star will be visible? (Ignoring weather, ie assuming some standard atmospheric condition).</p>

<star><observational-astronomy>
Standard conditions for a heliacal rising
Tyler Durden
# Standard conditions for a heliacal rising

(Asked by: username_0 on 2015-08-17)

I imagine there are several possible conditions for determining the time of a helical rising of a star, the elevation of the star at sunrise, the latitude of the observer, and the azimuth of the star.

Is there any kind of equation (or plot/graphic) that relates these variables and can be used to predict whether a star will be visible? (Ignoring weather, ie assuming some standard atmospheric condition).

**Tags:** star, observational-astronomy


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## 1 answers

### Answer by username_1 on 2015-11-28. Score: 1

What I do is compute the limiting magnitude for the position of the object I am interested in, and subtract it from the magnitude of the object (I call this the magnitude contrast). If negative, it should be visible with the naked eye. I use the function limmag\_jd() in the Fortran library [libTheSky](http://libthesky.sourceforge.net) for this.

In order to find the best moment in a given night, I compute the contrast for say every 15 minutes, and find the minimum. You can do this for a number of nights, until the best contrast found is negative, which would be the heliacal rising.

I'm not sure whether there is an easy way using a simple equation - the limiting magnitude will depend on things like the positions of Sun, Moon and the object in question, the phase of the Moon, the magnitude of the object, etc.


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