These images/animations were created by Prof. Andrea Ghez and her research team at UCLA and are from data sets obtained with the W. M. Keck Telescopes; image source; larger image
UCLA Galactic Center Group
The Andrea Ghez group at UCLA produced this image of our galaxy's center, showing stars tightly orbiting an object determined to be a black hole with a mass of 3.7 million suns. For more on this image and and how it was made, see UCLA Galactic Center Group and Stellar Orbits in the Central Arcsec. Don't miss this animation of the motion of these stars.
Visit Planetary Orbits for simulations of planetary orbits. For more about Kepler's Laws, which describe the orbits of planets, see this Hyperphysics page and Johannes Kepler: the Laws of Planetary Motion.