GreatCircle app for iPhone and iPad

The great circle (orthodrome) is behind the shortest distance between two points on the surface of our planet.
In the common display of the world, the great circle runs over the map as a sinus curve.

greatcircle, movement and gobal illumination(!):

greatcircle:
(1) This app calculates the curve on basis of two (user defined) points and displays it.
So you can see the path of the shortest distance.

movement and gobal Illumination:
(2) use the slider to move the plane along the great circle path and watch flighttime and distance remaining.
(3) at the same time: lighting of the earth is displayed!

So catch the app and
(1) Find out the reason why a flight from Los Angeles to Frankfurt proceeds so far in the north.
(2) See where and when on your way, the sun goes down.
(3) Are you arriving in the morning or evening?
(4) What happens when you move westbound with departure time in the morning?
(5) and so much more ...!

Hints:
To avoid missinterpretation or missunderstanding.
(1) This app displays the whole great circle, defined by departure and destination point. A flight from e.g. Denver to Bejing has two parts: a shorter via the northern part of the pacific ocean anda longer via the southern hemisphere, both are displayed.
(2) To get every point in the map (to mark from and to), just zoom in with two fingers.
(3) To define date and time of departure: local time is needed.