- About PSI
|PLANETS IN MOTION
PSI senior scientist Steve Kortenkamp specializes in developing ray-tracing computer codes to produce animations that demonstrate critical concepts in the Earth and space sciences. He uses planetary maps produced from NASA mission data and the open-source 'Persistence of Vision' ray tracing software. An example of how this is done is shown on the image to the left.
Two spheres are scaled to represent the true relative sizes of Earth and the moon (A). A white-light source is placed at a sufficient distance from the spheres to illuminate them with essentially parallel "rays" of light. A camera is set back from the spheres and captures the appearance of both spheres in the same scene. Then rectangular-projected images (B) of the Earth and the Moon are obtained from public domain web sites (e.g., NASA, U.S. Geological Survey) and digitally wrapped onto the spheres (C). Additional details such as the lunar orbit, Earth’s equator and its rotation axis are added to the scene (D).
For the animation, the motion of the Earth and Moon are recorded for a complete lunar cycle. Earth is rotated on its axis while the moon moves along its orbit. The moon is rotated at the same rate that it orbits Earth such that it keeps the same side facing Earth. For a typical animation, about 2000 individual frames are produced at high resolution. These frames are then "stitched" together at 60 frames per second to produce a 30 second full-screen animation of one complete lunar cycle.
One of the advantages of using this ray-tracing visualization technique is that the viewing geometry can be easily changed to give students several different perspectives of the same phenomenon. Once developed, the original code is essentially a computer model of the Earth-moon system that can be viewed from any position within the model. Additional concepts that can be visualized with this technique include, but are not limited to, Earth’s obliquity and the reasons for seasons; lunar and solar eclipses; comparisons between planets in terms of size, appearance and location in the solar system; effects of tides in the Earth-moon system; the distribution and motion of asteroids and comets within the solar system; comparisons between our solar system and many newly discovered extra-solar planetary systems.
Click on the links to the left for these animations and more!