Historical Models of the Solar System
Over the past 3000 years, humanity has seen great progress in the world of science, and even more tremendous advancements have been made in the field of astronomy. Many of these advancements have been pioneered by great men and women that spent their lives wondering about the world around us and why things work the way they do and why they are where they are. The greatest mystery for many of these people has been the deep, unknown realm of darkness that surrounds our mystical planet. This world, the Universe, in which our planet Earth is situated, has been a topic of great discussion over the last thousands of years and even then, there is so much that is yet to unfold.
Aristotle (384 BC – 322 BC)
Aristotle was one of the first minds to wonder about Universe and the Solar System in great depth. He was a highly respected figure and was one of the wisest philosophers and people in general to have ever lived. Aristotle’s interest in this topic was ignited Plato, another philosopher of Aristotle’s times who was very influential on the society he lived in. Plato asked the question of how the cyclical patterns in the sky could be explained. As an answer to this problem, Aristotle combined the works of Eudoxus and Pythagoras to develop a ‘geocentric’ model of the Universe. In this model, Earth was placed at the centre of the Universe and all other planets and stars were shown to be surrounding Earth.
Aristotle’s model could predict the motion of the planets with reasonable accuracy but could not explain any changes in brightness of the planets or the retrograde motion of the other planets (motion in the opposite direction to that of other bodies in the system) During the retrograde motion, the planets are typically at their brightest and Aristotle’s model did not explain this phenomenon.
Aristarchus (310 BC – 230 BC)
In the third century BC, a Greek astronomer who went by the name of Aristarchus of Samos developed a different model of the Universe. This model explained aspects that Aristotle’s model did not, such as retrograde motion, and was a much simpler representation of the Universe. His model, however, was ‘heliocentric’, meaning ‘Sun-centred’. His model also highlighted the changing brightness of the planets at certain points.
This model, even though it was very sophisticated and simple, was not accepted by most as it was difficult for them to acknowledge the fact that Earth as not at the centre of the Universe. Others also questioned the reliability of this model as it was not based on any valid measurements that Aristarchus made and hence there was no strong evidence to support his model.
Tycho Brahe (1546-1601)
Tycho Brahe was a Dutch nobleman and astronomer who managed to plot the night sky and study the night sky with extreme care and accuracy even though no telescopes had yet been developed. Brahe designed and constructed his own astronomical measuring instruments and used them for taking precise measurements. His thorough knowledge of the stars and the night sky allowed him to observe and record two supernovae during his life which was quite an accomplishment for an astronomer during his times.
Brahe’s own model was a mix of the geocentric and heliocentric models. His model had all of the planets revolving around the Sun with the exception of the Earth, as the Sun was shown to revolving around the Earth.
Brahe devised this model with the mentality that it is impossible for the Earth to be moving. This was because he lacked the technology to prove the movement of the Earth, and simply was left with no evidence for the matter. By showing a slight shift in the position of stars as Earth orbited the Sun, also known as the parallax effect, Brahe would have been able to provide evidence for a moving Earth and would have devised a completely different model, one that would be made out of the complete rejection of the geocentric model.
Johannes Kepler (1571 – 1630)
Johannes Kepler was the assistant of Tycho Brahe and was a brilliant mathematician that worked with Brahe in Prague. When Brahe died, it was Kepler who inherited all the gathered data of Brahe. Kepler, a believer of the Copernican model (heliocentric), used this raw data to find mathematical explanations for the motion of the planets. After working hard to combine this data with Copernicus’ model, Kepler reached the conclusion that the orbit of every planet is rather an ellipse than a circle. He applied this idea of an elliptical orbit to create his own model of the Universe, as shown in Figure 1.4.
The mathematics behind this model is described through three laws – The Law of Ellipses, The Law of Areas and the Law of Periods.
1. The Law of Ellipses states that each planet moves in an eclipse with the Sun at one focus.
2. The Law of Areas states that the speed of the planets along their elliptical orbits is such that they sweep out equal areas in equal periods of time. The basic meaning of this law is that the further the planets are from the Sun, the slower they will travel along their orbit.
3. The Law of Periods states that the period of the orbit of a planet is directly related to the average radius of the orbit that is followed by the planet.
Order of events: A timeline
Technology and historical models: An analysis
Technology has become a very important aspect of our lives now in the 21st century. Without it, the human race has relied heavily on their minds and bodies to work through things. This increased use of the mind has led to the creation of the older models and theories about the origin of the universe and what it is like. For instance, the Brahe model of the universe was a flawed model but had many correct aspects to it. This was because of the careful observation of the night sky that allowed Brahe to get some aspects of his model right. The flawed concepts of his model, however, were mainly present due to the lack of technology during his times. Brahe was unable to prove that the Earth is not a stable object in the universe, and this was because the lack of technology did not allow him to observe and explain the parallax effect which would have proved the movement of the Earth. If Brahe had a telescope with him, the idea of the parallax effect might have struck him and he would have been able to observe and note the change in the positions of stars in the night sky. The largest parallax of any star is less than one second of arc, or less than a thirtieth of Brahe’s best measurements. Again, his measurements whilst tremendous for his times, were incredibly affected by the lack of technology. Brahe created the most elegant of observatories, yet was unable to detect any parallax effect, which is why he never completely ruled out the geocentric model. Brahe’s model, even though heavily influential, was not accepted because of the lack of evidence to support the model – once again, the lack of technology failed astronomers of the old times.
Current theories on the origin of the Universe
The origin of the Universe has been a massively debated topic for many decades now, if not a few centuries. Even the likes of Albert Einstein have weighed in on the issue. Ultimately, for now, the conclusion that has been reached is that before everything, even before time began, there was one, single dot of matter. No outside to this dot, just the little packing of all matter, along with all the energy present now. This theory is now known as The Big Bang. The Big Bang Theory states that the Universe started out as a single ‘space particle’. The space particle was a hot, dense concentration of matter that ‘exploded’ into the form it is in now. The theory was extensively debated for many years, until two physicists, Stephen Hawking and Roger Penrose, in 1970, provided mathematical evidence, based on the theory of general relativity (put together by Einstein) proved that the Universe must have started out with a ‘big bang’.
Because of these mathematical accumulations of evidence, the Big Bang Theory is widely accepted across the world and even more evidence has emerged in support of the theory, such as cosmic microwave background radiation (CMBR), which was the extremely important, and the Hubble Expansion, which was also vital.
– Cosmic Wave Background Radiation (CMBR)
CMBR is the electromagnetic radiation that has been left over from an extremely early stage of the universe following the Big Bang. CMBR supports the Big Bang Theory as the theory is the only explanation so far for the existence of this radiation in the Universe. CMBR was detected by accident in the mid-1960s by Arno Penzias and Robert Wilson. They were using the Holmdel Horn Antenna in New Jersey to map the sky but ended up making this important discovery in the process. CMBR was later mapped with satellites, including the Wilkinson Microwave Anisotropy Probe (WMAP) which will further be discussed in the next section.
– Hubble Expansion
In 1929, Edwin Hubble declared that based on his observations of galaxies other than the Milky Way, he can conclude that the galaxies are moving away from Milky Way at a speed directly proportional to their distances from Milky Way. He states that the more distant the galaxy, the faster it was moving away from us. Based on Einstein’s General Relativity and his original predictions, Hubble had basically proved that the universe was expanding. Not only was this a revolutionary discovery, it also perfectly complimented the Big Bang Theory and provided much more evidence to support the theory which also speaks of an expanding universe. Hubble had gathered his data at the Mount Wilson observatory in California, where he worked, and used the most powerful telescope in the world at the time which was present at the observatory. Hubble’s ideas are demonstrated through the equation v = H0d, where ‘v’ is the velocity of a galaxy, ‘d’ is the distance to that galaxy and ‘H0’ is the Hubble constant.
Technology and the current theories
The creation of the Big Bang Theory has been influenced by a number of factors, but the availability and use of technology in the process has been the most important of them all. Many different types of technologies were used in the process of developing this theory, but some pieces have had a much greater contribution to this process. One of these technologies is the Wilkinson Microwave Anisotropy Probe (WMAP). The WMAP was launched in June 2001 as part of a project aimed at making fundamental measurements of cosmology. WMAP has been extremely successful through its project and played a major role in the increased acceptance and believability of the Big Bang Theory. The probe allowed for the mapping of the pattern of tiny fluctuations in the Cosmic Microwave Background Radiation (CMBR), which when studied, allow astronomers to infer a great amount of information about the early Universe. This piece of technology had many other contributions such as enabling the WMAP science team to determine the Universe to 13.77 billion years old, to within half a percent, based on the data provided by the probe.
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WMAP was an extremely crucial part of the development of the Big Bang theory. What started out as a bunch of ideas supported by numerous mathematical proofs, became the most widely accepted theory about the origin of the Universe ever, thanks to the evidence WMAP provided in context of CMBR. Without this, the Big Bang Theory would have been a great idea still, but would have never had CMBR as evidence as only the Big Bang Theory can explain the existence of this radiation. Although CMBR was discovered by mistake, it was only because the probe was developed enough to detect such electromagnetic radiation and provide logical and well organised data to the team that operated the probe.