Geocentric Orbit

Posted : admin On 1/29/2022

When looking at the comparisons between the geocentric theory vs heliocentric theory concepts, we find that there are two very different ways to look at the universe. In the geocentric theory, the Earth is essentially the center of the universe. The sun and other planets rotate around the Earth, giving us our day and night. In the heliocentric theory, the Earth rotates around the sun and this is a mechanism that is found throughout the rest of the universe.

The geocentric theory was developed in the early centuries of our BC modern calendar. For more than 1,000 years, it would dominate scientific thinking until astronomers and scientists could offer “proof” of the validity of the heliocentric theory. Today the idea that the Earth orbits the sun is what is generally accepted by the scientific community.

What Is the Scientific Evidence of the Geocentric Theory?

A geocentric orbit or Earth orbit involves any object orbiting Planet Earth, such as the Moon or artificial satellites. High Earth orbit (HEO) - Geocentric orbits with altitudes at apogee higher than that of the geosynchronous orbit. A special case of high Earth orbit is the highly elliptical orbit, where altitude at perigee is less than 2,000 kilometres (1,200 mi).

When people asked for scientific evidence that showed the geocentric theory was the correct model of the universe, there were three general key points that were made.

Geocentric Orbit
  • The Earth had to be the center of the universe (or at least the Solar System) because all things fall to the surface of the planet. This included objects that originated in space.
  • The motion of the stars, moon, sun, and the planets of our solar system could be explained by the perfect circles in the geocentric models of Ptolemy.
  • People are unable to feel the Earth move, which meant that the rest of the universe was likely moving around the planet instead.

The reason why these three key points remained scientific facts for more than 1,000 years was because there was no observed parallax of the stars. Those who supported geocentric theory stated that if no observed parallax was possible, then it discredited the validity of heliocentric theory. This was despite of the fact that critics of geocentric theory have existed since at least 200 BC when Aristarchus proposed that the Earth had to rotate around the sun due to the sheer size of the sun itself.

Ptolemy, about 4 centuries after Aristarchus, recognized that it would become necessary for the geocentric theory to be able to explain the motion of the heavenly bodies in a logical, scientific way. One of the methods that was used to solve the problem of orbits that were not pure circles was to include what he called “retrograde loops.”

This would help to explain why sometimes planets appeared to be moving “backward” in relation to an observer’s position on Earth. His terms of retrograde and prograde are still used today even though the heliocentric theory is considered to be proven and that planetary bodies have orbits that are more of an elliptical shape than a perfect circle.

It is an effect that occurs because when we look at the sky from our planet, the sun, moon, and stars appear to travel in a westerly direction. This is referred to as diurnal motion. Yet when a satellite orbits the planet, it can appear to be traveling in an easterly direction even though it is orbiting in the same direction as the sun, moon, and stars.

This effect occurs because the orbit of the satellite is faster than the rotation of the planet itself. There is one natural satellite, the moon Phobos for Mars, that offers a similar effect. Today we understand that the Earth rotates and this motion can be explained by the actual orbital effect of other satellites.

For those looking at geocentric theory, however, it was an ancient puzzle that would actually give us the word “planet.” The word comes from the Greek word for “wanderer.”

How Heliocentric Theory Was Proven to Be Correct

The initial concept of heliocentric theory placed the sun at the center of the universe. As we were able to peer deeper into space, however, we recognized that each star had the potential to be its own sun with planets that would orbit them. We saw that potential solar systems could orbit around their own central core. That galaxies could rotate around another center.

So the heliocentric theory applies throughout the entire universe. There is not necessarily a single center of the universe because it is continuing to expand, but several central points where orbits and rotation can be achieved.

It would not be until the 1500s when the mathematics of the heliocentric theory would be presented by Nicolaus Copernicus. Others, including Kepler and Galileo, would make observations that would support the Copernican Revolution in terms of Earth’s placement in the universe.

To counter the final argument that a parallax had not been observed, Friedrich Bessel proved that the parallax of a star was greater than 0 by measuring the parallax of star 61 Cygni in the mid-1800s. Vega and Alpha Centauri were also measured by Friedrich Struve the same year that Bessel provided his findings.

It would take a series of steps in the 1700s and 1800s for the heliocentric view to become widely accepted by the scientific community. The principle of relatively, for example, rules out the idea that our planet remains at a state of perpetual rest. Mach’s principle considers rest with respect to distant masses having special properties of velocity, which removes any centrism argument for either the sun or the Earth.

Is the Geocentric Theory Obsolete?

In the 1900s, Menachem Mendel Schneerson wrote that if the theory of relativity was being accepted as a scientific principle, then it would make the geocentric theory become obsolete. The theory of relativity encompasses the special and general relativity theories that were proposed by Albert Einstein.

Schneerson suggested that if two bodies in space are in motion that is relative to each other, then it would be impossible from a scientific standpoint to determine which object was rotating around the other. Not only would this idea then make the geocentric theory obsolete, but it would also make the heliocentric theory become obsolete as well.

This would be because it would be impossible to determine the stationary status of an object. Without at least some examination of this component, it would be an unscientific statement to say that Earth rotates around the sun or even that the sun rotates around the Earth. In some ways, it could even be argued that each planetary body rotates around each other, providing support to each orbital movement.

Some have suggested that not only is our solar system rotating around the sun, but that our sun is rotating around its own central nexus. This creates more movement through our universe than we even realize today. Several models have been suggested or offered to help explain or show how that movement could be taking place.

One of the most popular models places the solar system into the shape of a vortex instead of a relative circle. Could the heliocentric model be just as boring and incorrect to the vortex model as the geocentric theory was to the heliocentric theory so many years ago? Only time and additional observations and discoveries will help us to understand the full truth of our universe, solar system, and how we really live on this pale blue dot of ours.

What Geocentric Theory vs Heliocentric Theory Means Today

Because geocentric theory has been effectively disproven as a possibility for the state of the universe, it has become a term to refer to calculations that involve the Earth in some way. In such a system, the center-of-mass frame of the planet is therefore described as being geocentric, while a heliocentric frame is used to calculate velocity or angular momentum.

Using what we have discovered to be fact, we use heliocentric data today to be able to calculate the source of mechanical energy of a planet, asteroid, or other body in relation to how it moves around the sun. Smaller bodies can gain higher levels of heliocentric velocity because of the effects of gravity, while larger bodies, such as a planet, will have a heliocentric velocity that remains constant.

Geocentric Orbit Model

Through these measurements, if a constant velocity alters for some reason, it indicates that there has been a change in the mass of the body, the star it rotates around, or some other alteration has occurred within that solar system to affect its orbit.

The geocentric theory vs heliocentric theory debate may have been laid to rest more than a century ago and then confirmed with the discovery of other galaxies, but that doesn’t mean the ideas that were generated from such a debate have no meaning today. Ptolemy’s work, for example, to explain planetary movement helped us to refine our understanding of how real orbits operate.

As we take another trip around the sun, we’re experiencing heliocentric theory in its base form. Take a moment to appreciate that fact, even if something seems to be moving in the wrong direction when you look up into the sky.

Here is a picture of the earth orbiting around the sun. In order to plot the orbit of the earth, we need to use heliocentric (Sun-centered) longitude of the earth. However, all measurements give us geocentric (Earth-centered) longitude of the sun.

Here are the instructions on how to plot Earth's orbit.

1) Determine a coordinate system. Determine a starting point and the direction.

2) Find the measurements of geocentric longitude of the sun.

3) Convert the geocentric longitude to heliocentric longitude.

4) Plot Earth's orbit.

1) Determine a coordinate system. Determine a starting point and the direction.

Use 0 degrees (positive x-axis) as the direction from Earth to the Sun on the vernal equinox. The vernal equinox is when the sun crosses the celestial equator and when the length of day and night are approximately equal. There is also the autumnal equinox.

So in this picture, 0 degrees represent the direction to the Sun at the vernal equinox while 180 degrees represent the direction to the Sun at the autumnal equinox.

Orbital Velocity Formula

2) Find the measurements of geocentric longitude of the sun.

I went to the web site above to the dates of the vernal equinox and autumnal equinox. This web site will give you the dates starting from year 2000 until 2020. The vernal equinox for 2010 is March 20th and the autumnal equinox for 2010 is September 22nd.

Afterwards, I downloaded the The Astronomical Almanac in order to find the dates, geocentric longitude of the Sun, and the apparent size of the Sun for the current year. The Astronomical Almanac is almanac published by the United States Naval Observatory and Her Majesty's Nautical Almanac Office, containing solar system ephemeris and catalogs of selected stellar and extragalactic objects.


I'm going to use the data given by Mission Mathematics II: Grade 9 -12 on pg. 79. If you prefer to use actual data, you can look them up through internet.

DateGeocentric Longitude of the Sun (degrees)Apparent Size of the Sun (cm)
March 210

April 6

May 645.048.7
June 573.948.5
July 5102.548.1
August 5132.148.6
September 4162.049.0
October 4191.349.5
November 3220.149.7
December 4250.449.9
January 4283.250.0
February 4314.749.6
March 7346.049.5

3) Convert the geocentric longitude to heliocentric longitude.

Let's look at this picture again. In this picture, 0 degrees represents the direction to the Sun at the vernal equinox and the Sun is moving counterclockwise direction from the reference point. We need to change the picture so the Sun will be at the center, that is, looking back at Earth from the Sun.

In heliocentric coordinates, we are looking back at Earth from the Sun so the vernal equinox is at 180 degrees and the autumnal equinox is at 0 degrees and the Earth is moving clockwise.

DateGeocentric Longitude of the Sun (degrees)Heliocentric Longitude (degrees)Apparent Size of the Sun (cm)
March 210180

April 6

May 645.0225.048.7
June 573.9253.948.5
July 5102.5282.548.1
August 5132.1312.148.6
September 4162.0342.049.0
October 4191.311.349.5
November 3220.140.149.7
December 4250.470.449.9
January 4283.2103.250.0
February 4314.7134.749.6
March 7346.0166.049.5

I added 180 degrees from March 21 to September 4 and I subtracted 180 degrees from October 4 to March 7.

What is the mathematical reasoning behind this?

When you are changing from geocentric longitude to heliocentric longitude, it provides an opportunity to talk about reference point. When you look into the illustration of a geocentric model, the earth is in the center and the sun is moving counterclockwise from the right. In this model, earth is the reference point as the sun is changing. When you look into the illustration of a heliocentric model, the reference point has changed. Since the Sun is the new reference point, when it becomes the vernal equinox, earth is on the left of the sun.

Also, think about the direction on how the earth is portrayed moving from the sun. When you're standing on the earth, the sun moves in a counterclockwise direction. Or, more specifically, from 0 degrees to 180 degrees. However, when you're standing on the sun, the earth is moving clockwise from left to right from 180 degrees to 360 degrees. Therefore, when you're converting the longitude, you add 180 degrees starting from the vernal equinox until the autumnal equinox. After the autumnal equinox, you subtract 180 degrees.

4) Plot Earth's orbit.

Here is a picture I made using GSP.

I plotted the position of the earth using dilation and rotation in GSP.

Geocentric Orbit Of Mars

Using (1,0) as my starting point, I started with the longitude on October 4th. Heliocentric longitude is 11.3 degrees, so I rotated point (1,0) 11.3 degrees counterclockwise. After the rotation, I dilated the point 4.95 which is 49.5 divided by 10.

Geocentric Orbit Height

After that, I repeatedly rotated (1,0) to the heliocentric longitude given at a specific date and dilated the point one-tenth the size given in the table.

The picture above shows how close Earth's orbit is to a circle rather than an ellipical orbit we're used to see. The eccentricity of the Earth's orbit is currently about 0.0167, meaning that the Earth's orbit is nearly circular.