Cor Leonis

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.

Version 5.2 is currently available in all App Stores worldwide, fully localized to German and English.

Feedback, requests, and bug reports are welcome! Please send e-mail to cl(at)

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[These are a bit out of date, but the UI is still basically the same]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

Sagittarius (Archer) Northern summer sky Sun and planets near Taurus at daytime List of constellations and planets Ursa Major (Great Bear), with dark color scheme

Same screenshots from the German version:

Sagittarius (Schütze) Nördlicher Sommerhimmel Sonne und Planeten nahe Taurus, tagsüber Liste der Sternbilder und Planeten Ursa Major (Großer Bär), mit dunklem Farbschema


Cor Leonis contains a help page (accessible through the "i" at the bottom right) describing all the features. Here's what you get:

Where and When

  • Set place
  • Set time

Looking around

  • Swipe: Change view direction
  • N,E,S,W: Switch to cardinal direction
  • Choose constellation / planet from a list
  • Live mode: View direction follows device compass. Uses current device time and location.
  • 360° view of the hemisphere

What am I looking at?

  • Tap: Show information about constellation at this position
    • Web search for this constellation
    • The web links can be configured in the app settings ("Settings" on the home screen).
  • Three-finger tap: constellation lines on/off
  • toggle normal and dark color schemes

Web query configuration

If you want to change the preconfigured web links, you can change them in the settings panel for Cor Leonis (open "Settings" from the home screen and select "Cor Leonis"). Each link is similar to a bookmark in a web browser, but with placeholders for the current constellation you want to look up. These are the queries which come with the App:

  • Wikipedia:
  • ESA/Hubble:
  • Star Tales:

The syntax for the placeholders is pretty simple, these are the rules - they are also stated on the settings page, so there's no need to write this down :)

  • %NAME% ("Great Bear")
  • %NAMEX% ("GreatBear")
  • %NAME'Letter'% ("Great'Letter'Bear")
  • %LATIN% ("Ursa Major")
  • %LATINX% ("UrsaMajor")
  • %LATIN'Letter'% ("Ursa'Letter'Major")

What's next?

Bigger changes I am currently planning for:

  • Show nebulae, clusters, etc.
  • Display detailed information about sun and planets