Changing Models through History

In an article I located in Astronomy magazine online entitled, What are the Accepted Proofs that Earth Revolves Around the Sun? When Did This Realization Take Place?, the author quickly explores how the model of our solar system has changed over time, who was responsible for the ideas, and where we are today in our thoughts.  The author starts the reader out by pointing to Greek cosmology and its role in how we view the universe.  He brings up Aristotle’s geocentric model and how it remained the consistent thought of the universe until it was questioned by Aristarchus.

The reader’s attentions are then turned to Galileo and his views through a very early version of a telescope.  According to the author, Galileo’s views of Venus lead him to believe that Venus orbited closer to the Sun than Earth.  As our telescopes became more advance, our ability to see the motion of the Earth became clearer.  The author continues to lead the reader by showing them the Earth’s motion proved that it wasn’t stationary and lead other astronomers to begin to question the geocentric model of the universe.  But, the time frame for this detection took a while.

The next astronomer mentioned by the author was that of Friedrich Wilhelm Bessel who measured the parallax of a specific celestial body.  The author ends the article with a mention of English astronomer James Bradley and how Bradley was able to learn more about the Earth and its rotation around the Sun at a distinct tilt.

The geocentric view of the universe took a while to unravel because of the lack of ability to truly test the theories that may have been different.  The idea of the Earth being the center of the universe was established by the Greeks.  The Greeks were the first to not only try to look at the universe and understand how it works but to also write down their findings and reason among themselves regarding what they had found.  Aristarchus, although Greek, questioned the idea of Earth being the center of the universe and thought that the model of the solar system should have been Sun-centered.  The idea wasn’t widely accepted and was hard to prove at the time.  The Greek philosophers encountered a problem when they began to observe retrograde motion among the planets.

The Greeks utilized the Ptolemaic model to explain why some planets appeared to move in retrograde motion.  The Ptolemaic model, named after Claudius Ptolemy, attributed the retrograde motion to the planets moving around in their own circle while traveling around Earth which supposedly caused the planets to appear to travel backwards at certain points in their orbit.  The circles the planets traveled in were called epicycles and the larger orbit around Earth that they traveled was called a deferent.

As time went on, philosophers and early astronomers (although not called astronomers) began to notice that the planets didn’t travel in the same direction as Earth.  Hipparchus determined that the Earth moved in a way that allowed the celestial bodies in the sky to shift.  In other words, certain celestial bodies did not always reside in the same position.  For example, Polaris is considered to be our North Star.  However, it was not always the North Star and will not always be our North Star because of the motion of Earth.

Copernicus really proposed the heliocentric model of the universe.  He questioned the geocentric model and offered an explanation for the retrograde motion of the planets.  Galileo helped to contribute to the idea that the Sun was the center of the universe through his observation of different planets and the celestial bodies that orbited them.  Brahe measured the night sky with a giant protractor but struggled to prove that the Sun was the center of the Earth because of his lack of ability to accurately compute his findings.  Kepler utilized his gifts in math and science to make models of Brahe’s work.  He ended up discovering that the planet’s don’t travel in circles but in ellipses and the fact that they do orbit Earth.

In our lecture tutorials, we were able to confirm through practice inputting data that celestial bodies or planets that appear to move backward are actually moving in ellipses.  During a simulation in the overhead dome, we watched the planets as they traveled in their orbits in retrospect to the Sun and Earth.  When Mars traveled, it appeared to be moving backwards temporarily.  We learned that as Earth moves in its orbit around the Sun, it moves faster than certain planets like Mars (side note: which we later found out also has to do with the Earth’s closer distance to the central star, the Sun).  As it moves, it is as if it laps the other planet and the planet appears to be moving backwards temporarily.

It does amaze me how with the limited equipment and knowledge the early philosophers and astronomers had, they were still able to figure out some of the complexity that is our universe.  Kepler’s ideas still hold true today.




The Article that I looked at was called ” What Is The Difference Between The Geocentric and Heliocentric Models Of The Solar System”. In this article they first talked about the ancient Greeks and how they believed the planets in out solar system revolved around Earth with Earth being at the center of the Solar System, which stuck around for many centuries. Their were some who thought that the Sun laid at the center of the Solar System like Aristarchus of Samos, although his ideas really didn’t catch on until much later. In fact it wasn’t until the 15 and 16th century that some astronomers in Europe started to notice some irregularities like how Mars seemed to move backwards then forwards, along with some other flaws that they couldn’t explain. It wasn’t until Copernicus found Aristarchus work and used it to show how it was the Sun that was in the center of the Solar System ans that we along with the other planets revolve around the Sun. This new theory made sense of their found flaws of Geocentric and explained things like why Mars moved forward and backwards because the Earth orbits faster around the sun than other planets which makes it appear that way.

This relates to what we did in class because it talks about the retrograde motion of planets and explains why they seem to move backwards then forwards sometimes. Which we did in class during one of the lecture tutorials and slides shown in class. This particular article helped me better understand retrograde motion because they showed a picture in it how the Earth sees Mars as it moves. And the way the picture showed it just helped it click better for me.

I liked this article because it started at the beginning of the whole process between early astronomy and how Geocentric and Heliocentric became to be. This made it really easy and fun to follow and see how the story unfolded and became what we now know today.


Model of the Universe

In the article, What is the Heliocentric Model of the Universe?, Matt Williams explains how the heliocentric model was created by Nicolaus Copernicus, and how he was the most influential astronomy scholar because of his findings. He made ongoing observations and combined them with previous theories from “classical antiquity and the Islamic World”. He then composed the model of the Universe where the Earth, planets, and stars revolve around the Sun; and his theories paved the way for modern astronomy. His model created controversy among religions, but overtime his theories were accepted and applied. The heliocentric model eventually replaced the geocentric model, where Earth is the center of the Universe instead of the Sun; or The Ptolemaic Model created by Greek and Roman astronomers such as Aristotle.

This article is related to class because it further explains what Professor Morrison taught us through Lecture Tutorials and notes. Taking extensive notes from the Powerpoint slides and then following up with reading from the text helped me to grasp this objective. We also took a look at historical places that assisted this objective, such as the Stonehenge Rock in England. We also talked about retrograde and prograde motions, which describe the way the Earth, planets, and Stars move in the sky.

Honestly, this objective was so interesting, because instead of learning about astronomy we learned about the history behind how fascinated people were about the sky and the universe. It’s crazy to think that what we know today, people back then were arguing about and trying to figure out what the truth was without all the technology we have today.

Geocentric and Heliocentric Models

I found an article at that talks about the difference between Geocentric and Heliocentric models. Astronomers always would argue about if the Earth was the center or if the Sun is the center. The ancient astronomers did know that there were certain bright points that would appear to move among the background stars.

The ancient Greeks would include to consider the planets, Mercury, Venus, Mars, Jupiter, and Saturn, also including the Moon and the Sun. Not every Greek believed that the Earth was in the middle. According to NASA, Aristarchus of Samos, was the first person to say that the center of the universe was the sun. He said this in the third century but the idea stayed dormant for several centuries.

European scholars relied on Greek sources for thier education for centuries. But some stuff didn’t make any sense. By the fifteenth and sixteenth centuries, the astronomers in Europe were facing a lot more problems. The Eclipse tables were not being calculated correctly. Sailors needed to keep track of thier position when sailing. The calendar dating from the time of Julius Caesar which was no longer accurate in describing the equinox which was a big problem for officials concerning with the timing of religious holidays, mostly Easter. Later on the timing problem was solved by resetting the calendar and instituting more scientifically rigorous leap years.

It was Nicolaus Copernicus who took that understanding and applied it to astronomy. Copernicus published a 1543, Copernicus De Revolution Orbium Coelestium, which outlined the heliocentric universe similar to what we know today. According to Encyclopedia Britannica, was that the planets’ orbits should be plotted with respect to the “fixed point” Sun, that the Earth itself is a planet that is turned on its axis, and that when the axis changes directions with respect to the stars which causes the North Pole star to change over time. Newton’s gravity theory was later supplanted by Albert Einstein, who in the early 20th century proposed that gravity is instead a warping of spacetime by massive objects. The blog post and the article both talk about the difference between Geocentric and Heliocentric models of the solar system which is what my teacher was talking about on the powerpoint. We also went over it by doing some book work in the tutorial text book. I learned a lot about the history of the geocentric and heliocentric models. I used to get those models confused but now I know exactly which models is which. I think the article I presented was a good article to work with. I would recommend anyone to view it because it is very informative and it gets more in detail about the history and such. I feel like I learned a lot from this article. I couldn’t stop reading it, it was so fascinating about the information of the history it provided.

Heliocentric vs Geocentric

I stumbled upon an interesting article regarding the differences between the Heliocentric model of the solar system and the Geocentric model of the solar system. This article is titled  What is the difference between the Geocentric model and the Heliocentric model of the solar system? Written by Elizabeth Howell. She summarizes that the Geocentric model of the solar system means that it is “Earth centered” this concept was created by the ancient Greeks. The Greeks were the first people to discover the naked-eye planets which means that these planets were able to be seen without a telescope or some other piece of technology. According to the Greeks the Geocentric model breaks down into the concept that the planets Mercury, Venus, Mars, Saturn, and Jupiter as well as the sun and moon all revolve around the Earth making our planet the focal point of our solar system. This concept became very crucial in Greek culture because the Greeks would then continue on with naming astronomical phenomenons after Greek Gods. However, as time went on not all Greeks continued to believe and support this theory of our solar system. During the Third century BCE the Greek philosopher Aristarchus of Samos was the first person to claim that sun was the origin of our solar system, not planet Earth. Unfortunately, the Greek people of this time still relied on Greek sources of education. Aristotle and Ptolemy were the first people to describe the motions of our solar system as eclipses. After seeing the motions of Mars, Ptolemy claimed that the planets moved in circles within their respected orbit. Eventually, it was realized that these eclipses were inaccurate. It wasn’t until Nicolas Copernicus publishing in 1543 that his version of the Heliocentric model in which he broke down into being a sun-centered model of our solar system. This model explained all the orbits of the planets are cleared the misconception of the motions of Mars. Soon after this was published many people jumped on board with this model and ran with it. Johannes Kepler then developed his three laws of motion, then Isaac Newton developed his theory of gravitational force.

This article relates and explains the Fourth objective in our class, “I can describe how the Heliocentric model of the solar system was developed and why it was adopted over the Geocentric model of the universe.” after hearing all the lectures in class along with the notes that were taken our class has learned that the first idea of our solar system was Geocentric based and this was created by the ancient Greeks. The Geocentric model by the Greeks was based on the preference that planet Earth was the center of our universe  in which that all the naked-eye seeing planets along with the sun and the moon revolved around it. After a period of time a theory of system of ellipses were created to help explain the motions of the planets. This came about due to the fact that astronomers saw strange motions of planets in the night’s sky, particularly Mars. However, over time this theory became false because it could never explain the unmatched movement of the planets. Later on Nicolas Copernicus published his Heliocentric model of the universe during the Sixteenth century. This model was based on the concept that the sun was the center of our solar system and that the planets orbited around it in circles. Even though Copernicus was close his model was later modified in which our planet’s orbit the sun in ellipse patterns helping explain the movements of the planets.

This article and conceptual objective really relate to me personally because I’ve always found our particular solar system very interesting. I’ve always wanted to know the exact amount of time, speed, and distance the planets travel around our sun. When we were discussing the history of these models in class I already had some prior knowledge to some of these especially with the ancient philosophers like Copernicus and Aristotle. However, I never knew that Copernicus had his model of the Heliocentric theory modified I always thought that was correct. The more and more we review and discuss about different aspect or astronomy the more I find myself engaged. I found this objective quite favorable and interesting in my opinion.



Geocentric and Heliocentric Models

The article I found on is called “What is the Difference Between Geocentric and Heliocentric Models of the Solar System”. It told me how each of these models came to be. The ancient Greeks were able to see visible planets with the naked eye and saw them move against the background of the stars. From this, they assumed that the Earth was at the center and that all the planets and Sun were orbiting around (Geocentric). Not everyone believed that the Earth was the center but the people who didn’t were brushed off. Until the fifteenth and sixteenth centuries when European astronomers would notice that some planets, like Mars, would move backward and then move forward again. Copernicus applied the idea of a Heliocentric solar system into astronomy and this helped the understanding of how the planets orbit around the sun. This also explained why the planets seemed to move in a backward direction, because the Earth has a faster orbit around the Sun than other planets. Kepler’s laws came into view once the Heliocentric model was introduced.

This can relate to things we have done in class as well. We did lecture tutorials on Retrograde motion of planets. This helped my understanding of the models and how planets seem to be in retrograde because our planet is moving at a faster orbit around the sun.

I found this article interesting because it talked about all the different astronomers and scientists that were involved in the making of these models. How each model was thought of and how science improved over time to actually get it right.

Moving Backwards

In the article, “ What is retrograde motion?“, written by Christopher Crockett, he discusses the basics of retrograde motion and how it happens. Retrograde motion of Mars is caused by the illusion of Earth’s faster orbit around the Sun. While Mars move towards the east, for a few months it will appear to move backwards going towards the east. The image below is a great example from the article explaining how it works.Illustration of retrograde motion

If you where in Mercury, the Sun can have a retrograde motion once a year by rising twice on the same day.

My thoughts on this article are very positive. This is a great source for beginners like my self to learn more in depth about retrograde motion and how it effects the way we see planets move throughout our sky.

This article relates to our conceptual objective, ” I can describe how the heliocentric model of the solar system was developed and why it was adopted over the geocentric model of the universe”, because one of the main reason why the heliocentric model was adopted over the geocentric one was due to retrograde motion and how it didn’t make sense with the geocentric model. With the Ptolemaic model trying to explain retrograde motion with a geocentric model, the small circle called the epicycle or basically the orbit of a planet in a small orbit. This model showed to be successful and people back then thought it was correct and it helped explain retrograde motion. In class, we used the planetarium projector to see how Mars move towards the east in the sky and then moves backwards towards the west. This helped the class visualize how retrograde would’ve looked like if we were observing it at night.Image result for ptolemaic model

Copernicus began studying the solar system and adopted Aristarchus’s sun centered idea. He mad simple calculations strengthening his sun centered idea and helped him calculate orbital period and relative distances, which were not possible with the Earth centered solar system. Of course the only thing wrong with Copernicus’s model was that the orbits were perfect circles.

Image result for copernican model

The main reason these astronomers couldn’t really find out these problems were due to bad quality data. Tycho Brahe was able to make measurements for planetary motion with his observatory. Tycho Brahe couldn’t really explain the planetary motion so he hired someone who can named Johannes Kepler. After countless times of trying to match Tycho work with circular orbits, Kepler discovered that the orbits are circles but ellipse. With This information, the heliocentric model was adopted over the geocentric model due to retrograde motions and how its not possible for the orbits to be perfect circles.