#RETROGRADE MOTION COPERNICUS SERIES#

Note that an arrow illustrates the direction of apparent motion in the sky. A system of circular gears controls the positions of Earth and Mars and their rates of motion.Ī hand crank allows the demonstrator to advance Earth and Mars, while the gears ensure appropriate relative rates. East is counter-clockwise around this circle. Here, a white rod connects Earth and a superior planet similar to Mars and represents the perspective, pointing to the location where Mars would be seen in the sky from Earth. Earth and a superior planet in a circular orbit around it.

It consists of the sun at the center, in red. Let’s look at a demonstration for teaching retrograde motion. Nothing is changing in the planet’s motion, and retrograde motion occurs as a natural perspective effect. This is why retrograde motion is referred to as “apparent retrograde motion” by many. Thus, retrograde motion occurs over the time when the sun, Earth, and planet are aligned, and the planet is described as being at opposition – opposite the sun in the sky. Retrograde motion was simply a perspective effect caused when Earth passes a slower moving outer planet that makes the planet appear to be moving backwards relative to the background stars. In the 1500s, Copernicus explained retrograde motion with a far more simple, heliocentric theory that was largely correct. We know today that this explanation was completely wrong. This allowed the existence of retrograde loops to be explained, although in a complicated way. It was believed that Earth was at the center of everything and that a planet moved on a circular path called an epicycle, the center of which moved on a larger circle called the deferent. Two thousand years ago, the Greek astronomer Ptolemy explained retrograde motion with a geocentric system of wheels within wheels, kind of like the kids’ drawing game Spirograph. For superior planets, those that orbit the sun further out than Earth, and the only planets that will be discussed in this video, this effectively creates a loop in the sky. This apparent motion concerns the planet slowing in its eastward motion, stopping, moving westward for a while, and stopping again before continuing on its eastward journey. This video will focus on a variation of that motion known as retrograde motion. Note that a planet still rises in the east and sets in the west on any given night due to the rotation of Earth. Planets typically move eastward, the direction of increasing right ascension, which we know today is due to their revolution around the sun.

#RETROGRADE MOTION COPERNICUS SERIES#

This could be seen if you took a series of photos every night for a month with a chosen star highest in the sky and laid them over the top of each other. But if you note the location of a planet relative to the background stars, and note its location again several nights later, you will see that it has moved. The term “planet” originates from the Greek word for “wanderer.” This phenomenon can’t be really be seen on any given night. They change their position in the sky from night to night. However, planets move in the sky relative to the pattern of background stars. However, the pattern of stars that is seen in the sky, how far apart a pair of stars are seen from each other, stays the same over time scales of thousands of years.

In the night sky, stars rise and set due to the rotation of Earth. This is illustrated in the video Retrograde Motion (6 minutes, 25 seconds). His model was very successful, however, in solving the problem of retrograde motion in a very elegant manner. Although this solved many longstanding problems in the Ptolemaic model, Copernicus still believed that the orbits of planets must be circular, and so his model was not much more successful than Ptolemy’s in predicting the position of the planets. Copernicus proposed that the Sun was the center of the Solar System, with all of the planets known at that time orbiting the Sun, not the Earth. The astronomer given the credit for presenting the first version of our modern view of the Solar System is Nicolaus Copernicus, who was an advocate for the heliocentric, or Sun-centered model of the solar system. However, because even in its most complex form it still produced errors in its predictions of the positions of the planets in the sky, some astronomers continued to search for a better model. The geocentric model of the Solar System remained dominant for centuries.

Retrograde motion copernicus