Why do satellites arcs end abruptly when observed from Earth I recently got an app that let me track the ISS. I noticed that during the time it's visible, it disappears before reaching the horizon, and sometimes reappears soon after for a bit.

Can somebody explain to me how the ISS and other satellites orbit? Specifically, what makes their visible period such a narrow one, that doesn't span all the way down to the horizon? (which is what my layman brain expected)
Because satellites are only visible when they are in sunlight, they are not visible when they go into the Earth's shadow. The app most likely predicts where this occurs and ends the arc.

In other words, it does not make sense for an observer to look for a satellite when it is not visible, so there is no need to draw the path when it is in the shadow.