# How Did The Copernican Explain Retrograde Motion

According to Copernicus, the planets that were closest to the sun appeared to be moving backward because they were moving more quickly than those that were farther away.

## How does Copernicus explain retrograde motion?

Because of the Earth’s rotation, stars rise and set in the night sky. However, throughout thousands of years, the pattern of stars that can be seen in the sky and how far away stars can be viewed from one another remain constant. However, with relation to the arrangement of background stars, planets shift in the sky. From one night to the next, they move around in the sky. The Greek word for “wanderer” is where the word “planet” comes from. You can’t actually witness this phenomenon on any given night. However, if you observe a planet’s position in relation to the background stars and then observe it again a few nights later, you will notice that it has migrated. This could be seen if a month’s worth of nightly images were taken with a particular star at its greatest point in the sky and superimposed over one another. Since planets revolve around the sun, they normally migrate eastward, in the direction of rising right ascension. Due to Earth’s rotation, a planet still rises in the east and sets in the west on any given night. This video will concentrate on retrograde motion, a variant of that motion. This apparent motion involves the planet sluggishly travelling eastward, stopping, briefly going westward, and then stopping once again to resume its eastward motion. This basically creates a loop in the sky for superior planets, those that orbit the sun farther out than Earth, and the only planets that will be covered in this movie.

The Greek astronomer Ptolemy proposed a geocentric system of wheels within wheels, resembling the children’s drawing game Spirograph, to explain retrograde motion two thousand years ago. A planet was thought to move on an epicycle, a circular path with its center moving on a bigger circle known as the deferent. Earth was thought to be in the center of everything. This made it possible to describe retrograde loops, albeit in a convoluted manner. Today, we understand that this justification was wholly incorrect.

Copernicus developed a far more straightforward, but essentially accurate, heliocentric hypothesis to explain retrograde motion in the 1500s. It was only a perspective effect when Earth passed an outer planet because the slower-moving planet appeared to be travelling backwards in relation to the background stars. The planet is said to be in opposition to the sun in the sky when the sun, Earth, and planet are aligned, which is when retrograde motion occurs. Because of this, retrograde motion is also known as “apparent backward movement among many. The planet’s motion is unaltered, and retrograde motion arises as a result of a normal perspective effect. Let’s have a look at an illustration of retrograde motion. It has the sun in the middle, colored red. Earth is orbited by a superior planet in a sphere. The perspective is represented by a white rod that links Earth to a superior planet that resembles Mars and points to the region of the sky where Mars would be visible from Earth. Around this circle, east is to the right. The positions and speeds of motion of Earth and Mars are controlled by a system of circular gears.

The demonstrator advances Earth and Mars with a hand crank, and gears make sure that the relative speeds are correct. The direction of the apparent motion in the sky is depicted by an arrow, as you can see. Additionally, we have added background stars to the area where we will see Mars’ apparent position. We begin our display well before Mars will be in opposition. Keep in mind that Earth is already catching up to Mars and will soon pass it. Mars’ apparent location in the sky is indicated by the rod that connects Earth to Mars.

Mars is at first traveling slowly eastwards as we turn the crank to advance time. Currently, Mars looks to be moving retrogradely as its eastward motion appears to have stopped. Mars is currently traveling west, as you can see. At the midpoint of its retrograde journey, Mars hits opposition. We are now at the point when the westward velocity of Mars seems to stop. the cessation of backward motion Mars begins its regular eastward march in relation to the stars as we move through time. Keep in mind that perspective is solely to blame for this effect. Mars and Earth’s motions remained unchanged.

The perspective effect that underlies retrograde motion is shown in this diagram.

For the planet and earth coordinates stated, where does a superior planet appear to be placed in the sky? Please write your vote down on a piece of paper and describe how you arrived at your decision.

By drawing a line from earth through the planet and into the surrounding sky, one may replicate a line of sight and estimate the apparent location of the planet in the sky.

A number of values that describe the retrograde motion of superior planets are displayed in the table below. The synodic period is provided in the table. The period between oppositions, which is also the duration between retrograde motions, is how frequently Earth passes a superior planet. It should be noted that the synodic period becomes closer and closer to a year when one analyzes planets in bigger orbits. Specifically, for the planet “The synodic period for Far Out, which is on a very vast orbit, would be exactly one year since it would orbit so slowly that it would essentially remain stationary. Accordingly, the retrograde interval, or the amount of time spent migrating west, is shortest for Mars and increases to half a year for our own planet “Outer planet. Keep in mind that Mars has the greatest retrograde loop, or the angular extent of the backward-moving tract in the sky, and that it shrinks to zero for the “Outer planet. This can be explained in terms of how our perspective has changed. Mars is the planet closest to Earth, and as a result, it moves the most as Earth passes it. It can therefore appear to be in a wide variety of postures. The impact of perspective is greatest.

## How did Copernicus explain the stars’ elliptical motion?

• To explain the motion of planets in orbits with loops that could be observed, Copernicus proposed a straightforward theory of the solar system. The planets, including the Earth, revolved around the Sun, which he put at the center. By combining the planet’s basic motion in a circular orbit around the Sun with the Earth’s simple motion in its orbit around the Sun, he was able to explain the looped pattern of planetary motion through the stars. The motion of the Earth is what causes the loops.
• The epicycloids of Mars, Jupiter, and Saturn were explained by Copernicus by having them orbit objects in orbits larger than the Earth’s orbit. He caused Venus and Mercury to orbit the Sun in smaller orbits than the Earth. This explained their behavior, which is to stay close to the Sun and swing back and forth between its two sides.
• Additionally, Copernicus foresaw Venus’s phases, which were not noticed until the development of the telescope.

## How did Copernicus explain the sun’s motion?

The astronomical theory created by Nicolaus Copernicus and published in 1543 is known as Copernican heliocentrism. According to this theory, the Sun would be stationary in the center of the universe, and Earth and the other planets would orbit it at constant speeds in circular orbits modified by epicycles. The Ptolemaic geocentric model, which put Earth at the center of the universe and had been in use for millennia, was replaced by the Copernican model.

Even though he had shared a draft of his own heliocentric theory with colleagues before 1514, he didn’t decide to publish it until Rheticus, one of his students, pushed him to. Copernicus’ task was to more eloquently and precisely calculate the duration of a solar year while maintaining the metaphysical implications of a mathematically ordered world in order to offer a useful alternative to the Ptolemaic model. As a result, his heliocentric model kept some of the Ptolemaic features, leading to errors such the planets’ circular orbits, epicycles, and uniform speeds, while also using concepts like:

• The Earth is one of many planets that orbit a still sun in a specific order.
• The daily rotation, yearly revolution, and yearly axis tilting are the three motions of the Earth.
• The Earth’s motion explains why the planets’ retrograde motion occurs.
• The distance between the Sun and the stars is much greater than the distance between the Earth and the Sun.

## How was retrograde motion explained?

Claudius Ptolemy offered the most significant solution to this issue in the third century AD. A deferent and an epicycle, he contended, are the two sets of circles on which planets orbit. This provided an explanation for retrograde velocity that preserved the planets’ elliptical orbits around the Earth.

The idea of uniform circular motion was accepted by Copernicus without doubt. Although the Sun was at the center of the Copernican concept, the planets still moved uniformly in a circle around it. Therefore, without epicycles, the Copernican model could not account for all the specifics of planetary motion on the celestial sphere.

## How does the geocentric model explain retrograde motion?

The retrograde motion of the planets around smaller circular pathways that traveled around larger circular orbits around the Earth is explained by the geocentric model using a system of epicycles.

## How does the Ptolemaic model account for the planets’ apparent retrograde motion?

How does the Ptolemaic model account for the planets’ apparent retrograde motion? According to this theory, the planets orbited Earth in tiny circles that occasionally shifted backward as a result of their combined speed.

## Who was the first astronomer to offer an explanation for the planets’ apparent retrograde motion in the sky?

Although when looking at the night sky, planets can occasionally be mistaken for stars, the planets actually move in relation to the stars from night to night. As if the stars were revolving around the Earth, retrograde and prograde are noticed. The phrases retrograde and prograde were first used by the ancient Greek astronomer Ptolemy to describe how the planets moved in reference to the stars around 150 AD. Ptolemy held the view that the Earth was the center of the solar system. The same phrases are still used to describe how the planets move in respect to the stars as they are seen from Earth, despite the fact that we now know that the planets revolve around the sun. The planets appear to rise in the east and set in the west, just like the sun. A planet is said to be prograde when it moves toward the east in reference to the stars. Retrograde refers to a planet’s journey when it moves westward relative to the stars (opposite route).

## Which model can display animation in reverse?

By having the planets move on smaller circles connected to the larger circles on which they circled the Earth, the Ptolemiac model was able to explain retrograde motion.

## Did Copernicus think that everything moves in circles?

In his heliocentric system, Copernicus continued to adhere to strict Aristotelian principles: epicycles were still present, even though they were now focused on the Sun rather than the Earth. It called for smooth circular motion.