App: Solar Coaster
Developer: Stephen Lidie
Genres: Bildung, Dienst­programme

Solar Coaster visualizes the rise and set of Earth's nearest star, Sol, our Sun, and probes for upcoming solar and lunar eclipses. The App uses what astronomers call a local horizon coordinate system when displaying information, which essentially means that your current position is the center of the Universe and all calculated values are relative to you.

Solar Coaster's algorithms are accurate until 2100 AD, at all longitudes, and latitudes between -81° south and +82° north. Of course, you must have Location Services enabled and allow Solar Coaster to access your position for accurate simulation results, and to properly detect eclipses visible at your location.

A sinusoidal curve depicts Sol’s path for a single day, Today.  An artificial, horizontal, horizon line is drawn such that it intersects the curve at precisely two points, Sunrise and Sunset. This means that all points on the curve above the horizon are Day, and those below are Night. As the lengths of the Day and Night change this horizon shifts up and down the sinusoidal curve, and a trend direction triangle indicates how the shift is moving. The actual Sunrise and Sunset times are also displayed, in 12 or 24-hour format.

The point exactly midway along the Day portion of the sinusoidal curve is called Solar Noon, and represents the time of day Sol is farthest above the horizon. Solar Noon typically does not coincide with 12 o’clock Noon.

The point exactly midway along the Night portion of the sinusoidal curve is called Solar Midnight, and represents the time of day Sol is farthest below the horizon. Solar Midnight typically does not coincide with 12 o’clock Midnight.

Dawn precedes Sunrise, and Dusk succeeds Sunset. During these times of Morning Twilight and Evening Twilight Sol slowly brightens and dims appropriately.

Earth's nearest celestial neighbor, Luna, our Moon, sometimes makes appearances during the visualization.  At Moonrise a smaller, secondary, sinusoidal curve appears and Luna fades-in.  Luna is drawn with its proper phase, and rotated to the precise phase angle. At Moonset Luna fades-out.

Touching either Sol or Luna displays a tiny bit of additional realtime information (unavailable for the Today Extension and Screen Saver).

Once a minute orbital calculations are performed and the visualization is updated.  This means that if you are patient, very, very patient, you can watch Sol and Luna move! For those not so patient, touch the disclosure triangle and switch into manual You Drive mode (unavailable for the Today Extension and Screen Saver). The simulation is paused and the scene is augmented with informative data, various small, circular, marker points, three larger, colored, touch discs, Solar and Lunar Eclipse Probe controls, and a timer, which begins at +0:00, Now.

In You Drive mode:

 ⁃ Touching a marker displays its time (unavailable for the Today Extension and Screen Saver).
 - Touching the horizon line's trend direction triangle displays the amount of daylight.
 ⁃ Touching the cyan disc animates the simulation through the special marker times, and those times only.
 ⁃ Touching the orange disc animates the simulation through the entire day of 1,440 minutes.
 ⁃ Touching and sliding the yellow disc animates the simulation to a random minute of the day.
 - Touching an Eclipse Probe control initiates a search for upcoming solar or lunar eclipses, and if one is visible from your location the You Drive simulator is temporarily reset to that date and the eclipse circumstances are displayed.

The timer shows the elapsed time in hours and minutes of the simulation, whether positive or negative, relative to Now.

Touch the disclosure triangle once again to exit You Drive mode and resume the actual simulation.  Don't be surprised if you notice the visualization catch up for lost time.  And depending on what the time differential is and whether the simulation time is before or after Now, the tweening may be fast or slow or forward or reverse.

Release notes:
- Add instantaneous orbital velocity based on current distance.
- Add current moon phase name and illumination percentage.
- User interface and documentation improvements.
- Miscellanenous bug fixes.
- Minimum iOS version is 11.0 and minimum macOS version is 10.15.
- Update for iOS 16.1.1 and macOS 13.1.