One of my favorite iPad apps is Emerald Observatory, so when the original developers retired and open sourced the code, I volunteered to take over publishing it as an app in the App Store.

Picture of Emerald Observatory on an iPad

Emerald Observatory displays a wealth of astronomical information all on one screen, in a unique but understandable format. Information includes:

  • 12- and 24-hour ordinary clock time
  • Times of rise and set for the Sun, the Moon, and the 5 classical planets
  • Times of the beginning and ending of twilight
  • Heliocentric orrery (display of the planets in orbit around the Sun)
  • Altitude and azimuth for the same bodies (one body at a time)
  • Current phase and apparent orientation and relative size of the moon
  • Current regions of day and night on a world map
  • The Equation of Time, solar time, UTC time, and sidereal time
  • Month, day, year, and leap-year indicator
  • Daily alarm (delivered as local notification on iOS 4+ if app is not running)
  • Eclipse simulator

You can find the simple privacy policy for this app here.

You can find all the source code on Github (note that the source is five separate packages and that the build infrastructure isn’t entirely obvious; the repos are Observatory, esastro, eslocation, estime, and esutil).