航楽

KOURAKU is a visual educational app that lets you "see" and "manipulate" the science of navigation and positioning—the technology that allows people to cross the seas and determine their location. From classical celestial navigation to modern GPS, you can experience simulations and challenges along a timeline (from classical to modern).

As part of the Raku series of navigation modules, it is positioned alongside "KAIRAKU," which deals with marine science. While KAIRAKU focuses on the "science" of tides and ocean currents, KOURAKU focuses on the "technology" of using that knowledge to cross the seas. It includes six areas, ranging from high school earth science and physics to introductory levels of navigation and positioning.

【Observation and Challenge — The Learning Cycle】
Each mode can be used in two ways: "Observation" and "Challenge."

• Observation: Freely move the slider to see how the principles work.

• Challenge: Tackle tasks with hidden answers. Read instruments to "measure," calculate to "determine the position," and "check your answers." If you answer correctly, the thought process (calculation steps) will be displayed.

Each mode has 5 stages, for a total of 30 stages across 6 modes. Your progress is saved in the "Logbook" on the home screen, allowing you to easily check your progress.

【6 Modes】

■ Celestial Latitude

Measure the altitude of celestial bodies using a sextant to determine latitude. The altitude of the North Star is directly equal to the observer's latitude, and the altitude of the sun at noon can be used to calculate latitude using "90° - altitude + declination". In the challenge, align the sextant's scale with a star or the sun, read the altitude, and answer with the ship's latitude.

■ Longitude & Chronometer

Longitude is determined from the "time difference" between local noon and Greenwich Mean Time. Since the Earth rotates 15° per hour, the gain or loss of a clock directly corresponds to east-west position. Experience firsthand how chronometers, which maintain accurate time at sea, made longitude measurement possible.

■ Dead Reckoning
Estimate your current position by accumulating course and speed over time. Adding ocean currents visualizes how the estimated position gradually shifts from the true position. You can gradually challenge yourself, from calculating sailing distance to determining a course that takes ocean currents into account.

■ Chart & Compass
Convert the course taken with a compass to the true course by correcting for deviation and error (add for east, subtract for west). Conversely, you can also try "reverse calculation," determining the compass course to take from the true course on the chart.

■ Tides
The rise and fall of sea level caused by the moon and sun. Spring tides occur around the new moon and full moon, while neap tides occur around the first and last quarter moons. We read the times and heights of high and low tides from a 24-hour tidal curve to determine the time of day when boats can safely pass through shallow waterways.

■ GPS Positioning
Trilates is a method of determining position from the distance to multiple satellites. We determine the distance from the time it takes for radio waves to travel, and verify that even a slight error in the receiver's clock can significantly alter the position, and that the fourth satellite can correct that error.

【Features】
・6 modes x 5 stages, a total of 30 stages of challenges
・"Logbook" to record your progress (records can be deleted at any time)
・Each mode includes a principle/explanation sheet
・Each screen has a one-line "How to try" guide
・Structure traces the history from classical navigation to modern GPS along a timeline
・Supports 9 languages ​​(Japanese, English, Simplified/Traditional Chinese, Spanish, Portuguese (Brazil), Korean, German, French)
・Supports landscape display, large font size, and TalkBack
・Difficulty level indicators (Beginner, Standard, Advanced) and "Recommended" display, along with a start button on the home screen, make it easy to know where to begin
・Visuals in the style of nautical charts and logbooks. Dark/Light theme switching
- "About this app" screen with links to privacy policy and support
- All features available for free (banner ads only. No in-app purchases or subscriptions)

【Recommended for:】
- Students studying high school earth science, physics, navigation, or positioning
- Those who want to intuitively understand the mechanisms of celestial navigation, longitude, and dead reckoning
- Those interested in maritime affairs, ships, and geography
- Teachers who want to use it as teaching material
- Anyone who wants to properly understand how GPS determines location

* This app is a simplified simulation for educational purposes. Do not use it for actual navigation or positioning.