Why do retrograde loops occur

Life in the clouds of Venus? Maybe not. Cosmos: Origin and Fate of the Universe. Astronomy's Moon Globe. Galaxies by David Eicher. Astronomy Puzzles. Jon Lomberg Milky Way Posters. Astronomy for Kids.

Sign up. Table of Contents Subscribe Digital Editons. A chronicle of the first steps on the Moon , and what it took to get there. The Magazine News Observing. Photos Videos Blogs Community Shop. Sign up! Follow us: Facebook Twitter. Is it playfully looping about in its orbit around the sun or is something less strange going on? From EarthSky. Though it baffled ancient astronomers, we know now that retrograde planets are an illusion caused by the motion of Earth… You can test this the next time you pass a car on the highway.

As you approach the slower car, it is clearly moving in the same direction you are. Right as you pull along side and pass it, however, the car appears to move backwards for just a moment. As you continue pulling away, the car resumes its forward motion.

The same thing happens as Earth passes the slower moving outer planets. When we pass Jupiter, for example, the gas giant appears to reverse course in the sky for a couple of months. Draw a graph of planetary motion given its celestial coordinates at various times. Demonstrate ability to read a graph and its coordinates. Demonstrate undersanding of retrograde motion of a planet against the fixed star background Demonstrate undersanding of the geocentric and heliocentric explanations for retrograde motion Demonstrate ability to make conclusions about planetary motion from analysis of pictorial and graphical information.

Discuss the difficulties in determining the correctness of either the geocentric or the heliocentric explanations using observational data alone. Also see the relevant sections of program 4 [the celestial sphere] [the planets] ,program 7 [Plato's Question] , program 8 [Ptolemaic System] , program 9. Retrograde motion refers to the change of direction of the planets as they wander through the fixed background of the stars. Most of the time the nightly course is east to west in fairly predictable paths near the ecliptic.

Occasionally each planet turns around and moves to the east 'backwards' for awhile, then turns around to head westward again, making a loop or zig-zag against the star background. There are two good explanations or models to explain retrograde motion. One involves a geocentric view, where the sun and planets go around the Earth which is stationary. The other is a heliocentric view, where the earth and planets go around a stationary sun. For twenty five centuries or more people thought that the earth was the center of the universe.

They believed that the geocentric model explained the movements of the stars and planets, thinking that they revolved around the earth the way the celestial sphere appears to from our vantage point on earth. Today we have much evidence that the earth is just one of the many planets, and that it revolves around the sun once per year as it rotates on its own axis once per day.

It is easy to see why our ancestors thought the earth was the center of the universe when we watch the movement of the heavens. It is much easier to imagine that we are motionless at the center of a universe which revolves around us than to imagine the result of the combined daily rotation and annual revolution of earth. This is especially true when it comes to the motion of the other planets in relation to the earth's own moions..

It was the erratic motions of the planets that gave early astronomers problems. The motions of the stars, sun, and moon can easily be explained geocentrically. The retrograde motion of the planets is much more difficult to explain, especially if one is locked into a paradigm that insistst that all heavenly motiion must be circular.

Program 3 helped us to understand how paradigms affect thinking and perception, while programs 6, 7, 8, and 9 studied how the circular paradigm became so deeply entrenched.. Here is an animation of Mars in retrograde in KB.

It is speeded up one million times faster than the actual speed. The actual time spanned by the video is eight months. The video is in mp4 format and will require that you have Quicktime installed.