zoomy942 wrote:why is it that when something is unexplainable everyone think s it is a hoax? for some reason, it is the constant assumption of modern society that the farther we go back in time, to less people knew. we have no proof of all that. they may not be cataloging discoveries like we do, but what if, to them.. knowing about the stars or about some other advanced technology was logged on parchment or on cow hide. just because we dont use that or because we havent found theirs DOES NOT mean that older civilizations were primative.
. THE BIRTH OF MODERN ASTRONOMY
Before the 15th century AD where we basically have the beginnings of "modern" Astronomy as we will discuss below, the main contribution in Astronomy was done by the ancient Greeks between the 7th century BC up to about the 3rd century AD. For the first time in the human history superstition was replaced by reason. Some of the famous ancient Greeks that got us started to the road of understanding the mysteries of the universe were Thales, Anaximander, Pythagoras, Anaxagoras, Empedocles, Hippocrates, Democritus, Plato, Aristotle, Euclid, Aristarchus, Archimedes, Eratosthenes, Hipparchus, Lucretius, Ptolemy and Hypatia. These names are presented from the most ancient (around 7th century BC) to the most recent of the ancient era (around 3rd century AD) at which time the biggest library of the ancient times, that of Alexandria, was destroyed. With it all books of knowledge were burned leading humanity in dark ages until the Renaissance.
Aristarchus, Copernicus and the heliocentric model
The ancient astronomer Aristarchus, 310-230 BC, who was born in the Greek island of Samos, argued that the Earth is just another planet like the other five (the ancients knew of Mercury, Venus, Mars, Jupiter and Saturn) and that they all orbit the Sun. The model described by Aristarchus is called the heliocentric model (Sun-centered). Even though he was correct, his assertion was not accepted and had to be reintroduced about 1800 years later by Copernicus.
Aristarchus reasoned that the Earth rotates around an imaginary axis creating the day and night, and revolves around the Sun in one year. Aristarchus heliocentric model was revolutionary during a time that everyone believed in a geocentric view. Not only the heliocentric view was rejected by his contemporaries and he was accused for impiety, but was rejected by the rest of the world for almost 1800 years. Today, about 2300 years after Aristarchus, we still talk of a "rising" and "setting" Sun despite the untruth in the implications of the words. Aristotle and other philosophers of the same era tried to prove the heliocentric model by attempting to observe a stellar parallax of the foreground stars in relation to more distant background stars but they failed. Hence they concluded the Earth must not move around the Sun. Even though they failed, the effort of experimentation is commendable. Parallax is an apparent shift in the direction of an object as a result of the motion of the observer. Extent your hand in front of you and observe one finger first with your right eye having the left eye closed. Then repeat the same but this time with your left eye having the right eye closed and notice how the finger’s apparent direction is shifting with respect to the background objects. Of course a stellar parallax exists but is so small that is very difficult to observe without sensitive and complex devices. The Athenians used the eyes of Greek soldiers with the best vision but despite that they were unsuccessful.
Aristarchus did not believe in privileged reference frames, neither of the Earth nor of society. Today we know that the laws of Nature apply equally well everywhere in the universe and at all times. The universe is isotropic, that is, the view of the universe is similar in all directions and from all locations. No place is more privileged than another. A statement that can be made either on the grounds of human modesty, or can be deduced by existing modern theories of the laws of Nature. Ever since Aristarchus-and later Copernicus-we have been learning that we do not occupy a special place in the universe. The Earth is not the center of the Solar System, which is not the center of the Milky Way Galaxy, which is not the center of the universe, which has no center!
Copernicus, (1473-1543AD) was a Polish cleric trained in law and medicine but his main interest was Astronomy and Mathematics. In one of Copernicus’ own manuscript he writes about Aristarchus. That shows the influence Aristarchus had on Copernicus’ ideas. Copernicus reintroduced the heliocentric model of the solar system, and thus started a "modern" scientific revolution. He argued that the apparent annual motion of the Sun around the Earth (the ecliptic) is a result of the motion of the Earth around the Sun. Also, he said that the westward rotation of the celestial sphere can be accounted for by the eastward rotation of the Earth around its axis.
In his heliocentric model, Copernicus placed the planets nearest the Sun going outwards correctly as follows: Mercury, Venus, Earth, Mars, Jupiter and Saturn. These were the only known planets then. Further, he deduced that the closer a planet is to the Sun, the higher its orbital speed. He was able to explain the retrograde motion of the planets.
That Copernicus gets the credit of a heliocentric model when it is a well known historic fact that Aristarchus has discovered it first is of little importance. Generally speaking, it does not really matter who discovers something first. But Copernicus takes credit mostly because he went against the popular beliefs of the geocentric model (Aristarchus did the same thing of course) and that created an awakening of the sciences after they had been in darkness since the burning of the library of Alexandria.
Galileo and the Beginning of Modern Science (1564-1642)
Galileo (1564-1642) greatest contributions were in the field of mechanics, the study of motion and the actions of forces on objects and how the force accelerate them. Galileo adopted the Copernicus heliocentric system but in Roman Catholic Italy this was not a very popular philosophy. The church still upheld the ideas of Aristotle and Ptolemy who stated the Earth was the center of the universe. At the age of 69 Galileo stood trial for teaching the heliocentric model. The jurors were inclined to be lenient only if he repudiated his work. Galileo avoided death by reciting a prepared recantation and was sentenced to prison, later commuted by the pope to house arrest on Galileo's own estate. He died 9 years later.
Galileo constructed his first telescope, which made objects appear three times nearer and larger, and used it to make his first astronomical observations. Then on 1609, he constructed one with magnification 9. It was known that others before Galileo had constructed telescopes. But Galileo was the first one to use the telescope to observe the heavens. He found new stars not visible to the unaided eye, nebulous blurs resolved into many stars, and that the Milky Way (the strip of whiteness across the night sky) was also made up of many stars. He found moons around planets. This discovery was particularly important because it showed that not everything had to revolve directly around the Earth.
He also found that Venus goes through the same phases like the Moon, something that could only be accounted for by the motion of Venus around the Sun and not by any model in which Venus circled the Earth (fig. 1.16). Specifically this is so because, as it can be inferred by fig. 1.16 which shows both Venus and Earth orbiting the Sun, Venus may be seen by an Earth observer during early evening hours after sunset (evening "star"), or during a few hours before sunrise (morning "star"). This is in fact the case because Venus is orbiting the Sun and not the Earth. Furthermore, we will learn in lecture 3 when discussing the phases of the Moon that during full Moon the Moon rises at sunset and is up all night long. This is a result of the fact that the Moon is full when the Earth is between the Sun and Moon as the Moon revolves around the Earth. However, studying carefully fig. 1.16, when the phase of full Venus is approaching after the gibbous phase, Venus can be seen only briefly just after sunset or before sunrise, as required by a model of the Venus orbiting the Sun and not the Earth. Therefore, since during the full Venus phase, Venus is not out all night long as expected if Venus were revolving around the Earth and not the Sun, but instead is viewed briefly after sunset or before sunrise, Galileo concluded that Venus revolves around the Sun. Alternatively, one can argue that Venus circles the Sun and not the Earth by simultaneously realizing that: 1) Venus presents a complete set of phases like the Moon and 2) that such complete set of phases is observed while Venus is never opposite to the Sun (i.e. the full Venus phase is observed while the Sun and Venus are in the same general direction (as required by Venus circling the Sun) and not oppositely in the sky as (as would have been required if Venus circled the Earth. In the case of the full Moon, the Moon rises East at the same time as the Sun sets West, hence they are oppositely to one another, as required by the fact that the Moon circles the Earth.)).
(fig. 1.16)
Galileo also observed the Moon and he saw craters, mountains, and valleys. After his work it became increasingly difficult to deny the Copernican view. The church did not like that and condemned Galileo to house arrest.
Read the "Seeing for yourself" in Chapter 1 of the book.
. THE BIRTH OF MODERN ASTRONOMY
Before the 15th century AD where we basically have the beginnings of "modern" Astronomy as we will discuss below, the main contribution in Astronomy was done by the ancient Greeks between the 7th century BC up to about the 3rd century AD. For the first time in the human history superstition was replaced by reason. Some of the famous ancient Greeks that got us started to the road of understanding the mysteries of the universe were Thales, Anaximander, Pythagoras, Anaxagoras, Empedocles, Hippocrates, Democritus, Plato, Aristotle, Euclid, Aristarchus, Archimedes, Eratosthenes, Hipparchus, Lucretius, Ptolemy and Hypatia. These names are presented from the most ancient (around 7th century BC) to the most recent of the ancient era (around 3rd century AD) at which time the biggest library of the ancient times, that of Alexandria, was destroyed. With it all books of knowledge were burned leading humanity in dark ages until the Renaissance.
Aristarchus, Copernicus and the heliocentric model
The ancient astronomer Aristarchus, 310-230 BC, who was born in the Greek island of Samos, argued that the Earth is just another planet like the other five (the ancients knew of Mercury, Venus, Mars, Jupiter and Saturn) and that they all orbit the Sun. The model described by Aristarchus is called the heliocentric model (Sun-centered). Even though he was correct, his assertion was not accepted and had to be reintroduced about 1800 years later by Copernicus.
Aristarchus reasoned that the Earth rotates around an imaginary axis creating the day and night, and revolves around the Sun in one year. Aristarchus heliocentric model was revolutionary during a time that everyone believed in a geocentric view. Not only the heliocentric view was rejected by his contemporaries and he was accused for impiety, but was rejected by the rest of the world for almost 1800 years. Today, about 2300 years after Aristarchus, we still talk of a "rising" and "setting" Sun despite the untruth in the implications of the words. Aristotle and other philosophers of the same era tried to prove the heliocentric model by attempting to observe a stellar parallax of the foreground stars in relation to more distant background stars but they failed. Hence they concluded the Earth must not move around the Sun. Even though they failed, the effort of experimentation is commendable. Parallax is an apparent shift in the direction of an object as a result of the motion of the observer. Extent your hand in front of you and observe one finger first with your right eye having the left eye closed. Then repeat the same but this time with your left eye having the right eye closed and notice how the finger’s apparent direction is shifting with respect to the background objects. Of course a stellar parallax exists but is so small that is very difficult to observe without sensitive and complex devices. The Athenians used the eyes of Greek soldiers with the best vision but despite that they were unsuccessful.
Aristarchus did not believe in privileged reference frames, neither of the Earth nor of society. Today we know that the laws of Nature apply equally well everywhere in the universe and at all times. The universe is isotropic, that is, the view of the universe is similar in all directions and from all locations. No place is more privileged than another. A statement that can be made either on the grounds of human modesty, or can be deduced by existing modern theories of the laws of Nature. Ever since Aristarchus-and later Copernicus-we have been learning that we do not occupy a special place in the universe. The Earth is not the center of the Solar System, which is not the center of the Milky Way Galaxy, which is not the center of the universe, which has no center!
Copernicus, (1473-1543AD) was a Polish cleric trained in law and medicine but his main interest was Astronomy and Mathematics. In one of Copernicus’ own manuscript he writes about Aristarchus. That shows the influence Aristarchus had on Copernicus’ ideas. Copernicus reintroduced the heliocentric model of the solar system, and thus started a "modern" scientific revolution. He argued that the apparent annual motion of the Sun around the Earth (the ecliptic) is a result of the motion of the Earth around the Sun. Also, he said that the westward rotation of the celestial sphere can be accounted for by the eastward rotation of the Earth around its axis.
In his heliocentric model, Copernicus placed the planets nearest the Sun going outwards correctly as follows: Mercury, Venus, Earth, Mars, Jupiter and Saturn. These were the only known planets then. Further, he deduced that the closer a planet is to the Sun, the higher its orbital speed. He was able to explain the retrograde motion of the planets.
That Copernicus gets the credit of a heliocentric model when it is a well known historic fact that Aristarchus has discovered it first is of little importance. Generally speaking, it does not really matter who discovers something first. But Copernicus takes credit mostly because he went against the popular beliefs of the geocentric model (Aristarchus did the same thing of course) and that created an awakening of the sciences after they had been in darkness since the burning of the library of Alexandria.
Galileo and the Beginning of Modern Science (1564-1642)
Galileo (1564-1642) greatest contributions were in the field of mechanics, the study of motion and the actions of forces on objects and how the force accelerate them. Galileo adopted the Copernicus heliocentric system but in Roman Catholic Italy this was not a very popular philosophy. The church still upheld the ideas of Aristotle and Ptolemy who stated the Earth was the center of the universe. At the age of 69 Galileo stood trial for teaching the heliocentric model. The jurors were inclined to be lenient only if he repudiated his work. Galileo avoided death by reciting a prepared recantation and was sentenced to prison, later commuted by the pope to house arrest on Galileo's own estate. He died 9 years later.
Galileo constructed his first telescope, which made objects appear three times nearer and larger, and used it to make his first astronomical observations. Then on 1609, he constructed one with magnification 9. It was known that others before Galileo had constructed telescopes. But Galileo was the first one to use the telescope to observe the heavens. He found new stars not visible to the unaided eye, nebulous blurs resolved into many stars, and that the Milky Way (the strip of whiteness across the night sky) was also made up of many stars. He found moons around planets. This discovery was particularly important because it showed that not everything had to revolve directly around the Earth.
He also found that Venus goes through the same phases like the Moon, something that could only be accounted for by the motion of Venus around the Sun and not by any model in which Venus circled the Earth (fig. 1.16). Specifically this is so because, as it can be inferred by fig. 1.16 which shows both Venus and Earth orbiting the Sun, Venus may be seen by an Earth observer during early evening hours after sunset (evening "star"), or during a few hours before sunrise (morning "star"). This is in fact the case because Venus is orbiting the Sun and not the Earth. Furthermore, we will learn in lecture 3 when discussing the phases of the Moon that during full Moon the Moon rises at sunset and is up all night long. This is a result of the fact that the Moon is full when the Earth is between the Sun and Moon as the Moon revolves around the Earth. However, studying carefully fig. 1.16, when the phase of full Venus is approaching after the gibbous phase, Venus can be seen only briefly just after sunset or before sunrise, as required by a model of the Venus orbiting the Sun and not the Earth. Therefore, since during the full Venus phase, Venus is not out all night long as expected if Venus were revolving around the Earth and not the Sun, but instead is viewed briefly after sunset or before sunrise, Galileo concluded that Venus revolves around the Sun. Alternatively, one can argue that Venus circles the Sun and not the Earth by simultaneously realizing that: 1) Venus presents a complete set of phases like the Moon and 2) that such complete set of phases is observed while Venus is never opposite to the Sun (i.e. the full Venus phase is observed while the Sun and Venus are in the same general direction (as required by Venus circling the Sun) and not oppositely in the sky as (as would have been required if Venus circled the Earth. In the case of the full Moon, the Moon rises East at the same time as the Sun sets West, hence they are oppositely to one another, as required by the fact that the Moon circles the Earth.)).
(fig. 1.16)
Galileo also observed the Moon and he saw craters, mountains, and valleys. After his work it became increasingly difficult to deny the Copernican view. The church did not like that and condemned Galileo to house arrest.
Read the "Seeing for yourself" in Chapter 1 of the book.
