星楽

SEIRAKU is an educational simulation app that allows you to interactively experience the physical phenomena of celestial mechanics.

This is the sixth installment in the series, following SUUGAKU (Mathematics), BUTURAKU (Physics), DENRAKU (Electronics), HARAKU (Waves), and NETURAKU (Heat). This time, the theme is "Celestial Mechanics." Through 10 simulations, you can enjoy learning about the beauty and depth of the laws of mechanics that govern the universe.

【10 Simulations】

■ Orbital Motion: Simulate the orbital motion of planets due to the gravity of a central celestial body. You can freely adjust mass, velocity, and the number of planets, and observe the beautiful trajectories of planets with stable orbital calculations.

■ Universal Gravitation: Visualize the gravitational field created by multiple mass bodies with vector arrows. Tap the screen to add test particles and observe their motion within the gravitational field.

■ Three-Body Problem: Experience the complex motion of three stars pulling on each other. Choose from four types of orbital configurations—stable triangle, figure-eight, series, and unstable—to intuitively learn the relationship between gravity and velocity.

■ Tidal Force
Visualize the tidal deformation caused by the Moon's gravity on Earth. Observe how tidal force vectors and sea surface bulges change in real time, and learn the concept of the Roche limit.

■ Kepler's Laws
Experience Kepler's three laws of planetary motion on a single screen. Change the eccentricity and semi-major axis of an elliptical orbit to visualize the law of constant areal velocity using the sweep area.

■ Gravity Swing-by
Simulate the acceleration and deceleration of a spacecraft using planetary gravity. Adjust planetary mass, launch velocity, and approach offset to observe orbital changes and velocity gain.

■ Hohmann Transfer Orbit
Visualize the classic two-burner transfer connecting inner and outer circular orbits with minimal fuel. Δv, half-transition time, and elliptic eccentricity are displayed in real time.

■ Exoplanet Transits
Simulate the dimming of light as a planet passes in front of a star, along with a light curve. Observe the changes in transit depth and shape by adjusting the planetary ratio and impact parameters.

■ Gravitational Lensing
Visualize gravitational lensing, where light passing near a massive celestial body is bent. By changing the lens mass and light source position, observe how parallel rays converge at the focal point and the Einstein rings.

■ Precession
Visualize the precession of a rotating celestial body, where the rotation axis slowly traces a cone due to gravitational torque, in pseudo-3D. Experience Earth's precession and the shift of polar stars by changing the tilt, rotation speed, and torque.

【Features】
・Parameters can be adjusted in real time for all simulations
・Physical formulas and values ​​are displayed in real time
・Dark mode / Light mode support
・Intuitive and beautiful UI
・Supports Japanese / English
・Advertisements are only displayed as banners at the bottom of the screen

【Pricing and Billing】
・This app is free to use.

・There are no in-app purchases. • Revenue is supported by advertising (Google AdMob banner ads).

【Recommended for:】
• Students studying celestial mechanics in physics classes
• Those who want to intuitively understand the laws of the universe
• Teachers who want to use it as teaching material
• Anyone interested in astronomy or space