'Universe Sandbox' the gravity simulator

Fig: simulation of Saturn and Saturn’s Moons inside Universe Sandbox.

Universe Sandbox was designed and is developed by Dan Dixon, who worked on this educational project for over fifteen years before launching version 1.0 in May 2008.Universe Sandbox version 2.0 was released on May 2, 2010. It is an interactive space gravity simulator. Using Universe Sandbox, one can see the effects of gravity on objects in the universe and run scale simulations of our Solar System, various galaxies or other simulations, while at the same time, interacting and maintaining control over gravity, time, and other objects in the universe (moons, planets, asteroids, comets, black holes, etc.) Currently this software is only available for Windows based PCs.

Features:

This is a list of the key features of Universe Sandbox:

* Interactive n-body gravity simulator
* Simple tutorial introduction
* Several step-by-step activities included
* All units are measured in real units: kilograms, meters, seconds, etc.
* User control of the speed of time, gravity and other factors
* Simulation files are editable
* 3D Mode for use with red & cyan 3D glasses (anaglyph stereoscopic)
* Support for 3D DLP HD televisions
* Multiple color modes to help visualize and differentiate speeds and accelerations
* Two collision modes, Bounce and Combine
* Scaled ring systems of Saturn, Jupiter, Uranus, and Neptune, and generate rings around bodies
* Particle grids can be used to create 2D computer graphics or 3D computer graphics particle grids and then you warp/distort the grids and watch the gravitational effects by adding in moving planets or other objects (not in version 2)
* "Line-up/chart" mode option shows a visual size comparison of the stars and planets
* Includes the full sky panoramic view of the Milky Way from Axel Mellinger's photography of the Milky Way
* Can capture high resolution screen shots

Simulations:

Many simulations are included with Universe Sandbox, both realistic and fictional simulations.

* Our Solar System which includes the 8 planets, 5 minor planets, 160+ moons, and hundreds of asteroids
* The Andromeda & Milky Way galaxy collision which will occur in 4.5 billion years
* The 100 largest bodies in our Solar System
* The nearest 1000 stars to our Sun
* The nearest 70 Galaxies to the Milky Way
* A visual size comparison of the largest known stars and planets
* The Apophis asteroid passing near Earth in the year 2029
* The comet, Shoemaker Levy 9’s collision with Jupiter
* The 2008 KV42, a recently discovered comet with a retrograde motion orbit
* Moons converging into a single planet
* The Rho Cancri Solar System (55 Cancri) – which is a star with 5 known planets
* The Pioneer & Voyager encounters with Jupiter, Saturn, Uranus, & Neptune
* Visual Lagrange points of the Earth & Moon
* Gamma Ray Burst locations

Limitations:

This is a list of a few limitations of Universe Sandbox:

* Only runs on Windows based PCs
* The bounce collision mode is unrealistic
* When large bodies collide there is so much energy and heat that the bodies would meld together
* Ring positions relative to planets and moons are approximated
* Planet axis orientation relative to the solar plane is approximated and often inaccurate
* Galaxy simulations don't consider dark matter or account for the galaxy rotation problem