Why does retrograde motion occur

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. Mars repeats its retrograde motion every 26 months, but each retrograde episode traces a slighty different path, so there is no way to predict in advance how your graph will look.

It might be a loop to the left, a loop to the right, or merely a zig-zag. Here is an mp4 animation of 4 consecutive retrograde episodes of Mars.

Remember when watching that the retrograde phases occur every 26 months, so this is speeded up eight and one half million times. In this exercise you to plot and graphically observe the retrograde motion of Mars during the period from October to May , and it will allow you to see how it can be explained by both a geogentric and a heliocentric model.

Although drawing the graph is an important part of the exercise it is not the promary objective. While working on this exercise you should think about what the graph represents the actual motion of Mars through the sky during one particular retrograde episode , and also how you might explain this motion.

Try your best to keep your prejudices e. You will probably find it difficult to do so! Table 1 gives the actual location in the night sky of Mars for at ten day intervals in - 71 when retrograde motion occurred. The numbers in table 1 are the coordinates on the small section of the celestial grid in which the motion occurred. Right ascension and declination are coordinates on the celestial sphere.

Right ascension is measured in hours and minutes west of the vernal equinox, declination is measured in degrees and minutes from the celestial equator. Click for more information about graphing. Click here for the coordinates in decimal form for plotting in Excel or other graphing software.

Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas. Q: On page 51 of the February issue, there is a picture claiming to show Venus in retrograde. So please explain how Venus could be in retrograde, or was this a mistake? Turns out, Venus almost has tectonic plates. How to see the Venus and Mars conjunction this month. The surface of Venus moves like ice floating on an ocean. NASA is returning to Venus to learn whether the hot poisonous wasteland was ever habitable.

NASA to return to Venus with two missions by What echoing radio waves taught us about Venus. Ask Astro : What would Earth look like from Venus? Life in the clouds of Venus? Have a friend walk forward slowly. Now you walk forward at a faster speed. Watch your friend and think about how they are moving relative to you. At first, they move away, then as you pass them, they APPEAR to be moving backward relative to you - even though they are still walking forward.

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