Cor Leonis is…

… an App for Apple’s iPad, iPhone, and iPod Touch, displaying the night sky with its constellations, the sun (during the day), the planets, and the moon.

Cor Leonis’ user interface is simple and accessible, with the primary goal of helping to identify any of the 88 constellations of the night sky, offering historical background information and other interesting facts.

Sadly, the app is not available in the App Store any longer. The effort for maintainance and keeping up with current iOS releases just kept getting too high. Most of the astronomical algorithms are still in use in my VR astronomy app, Pocket Observatory.

Easy navigation

In traditional star charts, and also in many modern 3D applications where the viewer is floating in the middle of an imaginary sphere, it’s not always easy to compare the display to a real-world sky view. For better visual orientation, Cor Leonis features:

  • a realistic view window corresponding to the size of the iPad display, and a rendering of an actual horizon with landscape – it’s easy to see whether a constellation is rather small or spans half the sky
  • a compass displaying the cardinal directions and also the vertical view angle
  • a 360 degree view of the hemisphere, with a seamlessly animated transition from and to the current first person view – to avoid losing context


If you want to remember the many constellations and understand the connections between them, it helps a lot to learn about their origins and the often very beautiful background stories. Cor Leonis provides:

  • Built-in texts, summarizing facts about origin and mythology for each constellation
  • Preconfigured, editable web links to conviently browse the Web for more information when you’re connected to the Internet


[These are a bit out of date, but the UI is still basically the same]

Screenshots from the international version (note: these are all in portrait, but landscape orientation is of course also supported for a wider horizontal view angle):

Same screenshots from the German version: