Open-Source Solar System Simulator Gravity Visualizes Gravity and Orbits

The open-source solar system simulator “Gravity” is drawing attention. This software is an educational tool that visualizes the principles of gravity and the mechanics of planetary orbits through interactive animations. Through 24 progressive scenarios, it is designed to allow both children and adults to intuitively understand the dynamics of the solar system.

Gravity’s greatest feature lies in its visual presentation of abstract physical concepts. It provides a mechanism to derive answers through simulation to common questions from children, such as “Why doesn’t the Earth fall into the Sun?” and “How do rockets escape into space?” Rather than mere explanation, users can experience the laws of physics by manipulating the simulation themselves.

Technical Background and Data Accuracy

This simulator is built based on actual observation data. The size of each celestial body reflects its actual mean radius (from the Sun’s 696,340 km down to Pluto’s 1,188 km) and its mass. For orbit calculations, it uses J2000.0 heliocentric Keplerian elements obtained from the approximate orbital element tables of JPL (Jet Propulsion Laboratory) and the IAU (International Astronomical Union). By solving Kepler’s equation for six elements—semi-major axis, eccentricity, inclination, longitude of ascending node, longitude of perihelion, and mean longitude—in each frame, it reproduces realistic motion.

The time axis also follows the actual calendar. T=0 corresponds to the J2000 epoch (January 1, 2000, 12:00), and the simulation clock synchronizes with real time. The only scaling adjustment in rendering is explained as a measure to ensure visibility.

24 Interactive Scenarios

Gravity offers 24 animations that allow learning step by step from basics to applications. Each scenario is independent and focuses on a specific physical law.

The first scenario, “What is Gravity?”, displays two masses and the equal and opposite force vectors acting between them. It visualizes Newton’s third law, showing how the same force produces different effects on different masses. “Gravity Forms the Sun” animates the accretion process where a dust cloud contracts and rotates to form the Sun. “Gravity Forms the Earth” depicts similar microscopic processes within the remaining disk, showing the newly formed Earth glowing from the heat of its formation.

In the scenario “Moving Objects Keep Moving”, it presents what happens if the Sun is removed: the Earth drifts in a straight line at constant speed. This concretely demonstrates Newton’s first law, the principle of inertia. One of the most educationally valuable scenarios is “Why Doesn’t the Earth Fall into the Sun?” It juxtaposes the velocity vector and the gravitational force vector, and also displays a dotted line for the straight-line path when gravity is absent. It visualizes the process by which gravity bends a straight line into a closed loop, allowing an intuitive understanding of the principle: “An orbit is falling but always missing.”

The remaining 19 scenarios similarly cover a wide range of themes, such as gravitational interactions between planets, rocket orbit insertion, and satellite motion. Each scenario adopts a SpaceX-style UI, giving it a modern appearance.

Value as an Educational Tool

Gravity plays an important role in the field of education. Its strength lies in allowing real-time manipulation and observation of “force vectors” and “orbit formation processes” that are difficult to convey with traditional textbooks or video explanations. Users can change the mass of celestial bodies or adjust the initial velocity to immediately see the resulting changes.

Especially for children’s education, simulators are powerful teaching materials. Even for younger ages with underdeveloped abstract thinking, they can understand cause-and-effect relationships through visual feedback. According to the source, there are documented cases where children watched all 24 scenarios with focused attention, suggesting a high level of immersion.

The fact that it is open-source is also a crucial factor. The source code is published on GitHub, allowing educational institutions and developers to freely modify and redistribute it. It is possible to customize it for classroom use or add specific celestial phenomena. Moreover, bug fixes and feature additions by the community can be expected.

Operating Environment and Access

Gravity runs directly in a web browser. No dedicated installation is required; simply access the URL to start using it. It is currently available on the official website (gravity.appinn.com). The source code can be obtained from the GitHub repository, and it also supports local execution and modification.

Because it is browser-based, it runs regardless of the operating system. It provides the same experience on major platforms such as Windows, macOS, Linux, and Chromebook. It achieves smooth animation using WebGL-based 3D rendering.

Editorial Opinion

In the short term, this simulator is expected to see adoption in educational settings. Especially in the astronomy field within science education, it can greatly complement teachers’ instructional abilities by presenting dynamic phenomena that traditional models and illustrations cannot fully represent. Amid concerns about students losing interest in science, interactive materials have the potential to improve learning motivation. Furthermore, being open-source, community activities such as customization to fit school IT environments and translation into local languages are likely to become active.

From a long-term perspective, such visualization tools can be evaluated as contributing to raising overall scientific literacy. By sparking interest in space and physics at an early stage, it could lead to the cultivation of future STEM talent. Additionally, as open-source educational tools increase, the democratization of teaching materials will progress. It can be said that an environment is being developed where anyone can access high-quality science education without relying on expensive commercial simulators.

An editorial question remains: What degree of educational effectiveness will this simulator actually demonstrate? Quantitative verification is awaited. If test data measuring learners’ comprehension and comparative studies with traditional materials are published, they would provide strong evidence for adoption decisions. We also look forward to future developments regarding how the community will develop extension functions.

References

• Gravity – A Physics-Based Solar System Simulator - Small Software — Published 2026-06-14
• Gravity Official Website
• GitHub Repository (Not explicitly mentioned in the article, please check the link from the official website)