In Euclidean geometry, the ORTHOCENTER is the intersection of the three altitudes of a triangle. In other words, the altitudes are concurrent at the orthocenter. In the sketch below, the [color=#FF0000]RED[/color] great circles are the altitudes of the [color=#0000FF]BLUE[/color] triangle, and the [color=#FF0000]RED[/color] point is the point of concurrency of the altitudes; the spherical orthocenter.
Drag the blue points around, but do so slowly! Things change quickly on a sphere!
