History of Astronomy

Chapter 2: Early Astronomy
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Aristarchus c. Eratosthenes c. Hipparchus c. Nicolas Copernicus lived and worked in what is now Poland.

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Because of his long and abiding relationship with the Christian Church, he hesitated to publish his revolutionary ideas in astronomy, so he distributed an unsigned pamphlet in , which outlined his hypothesis of a heliocentric sun-centered solar system. Copernicus worked on his book, De Revolutionibus , over a period of many years.

It was published in , when he realized he was dying.

The Copernican system explained retrograde motion without epicycles, and was elegant and simple compared to the Ptolemaic system. Tycho Brahe was a Danish nobleman. He developed new and better instruments for viewing the stars, sun, moon, and planets. Telescopes had not yet been invented. To assist him, he hired other mathematicians and astronomers, including Johann Kepler. Johann Kepler I was born in what is now southern Germany. Ten days before Brahe died, in , he asked that Kepler be made imperial mathematician. Upon Brahe's death, Kepler inherited his records.

The scope of astronomy

Using Brahe's tables of the positions of the planets, Kepler was able to deduce his three laws of planetary motion:. Kepler's laws are empirical based on observations. They do not describe the causes of the motion; they only predict where the planets will be in the future. Galileo Galilei was born in Pisa, Italy. Galileo was the first scientist to make systematic use of the telescope in looking at the heavens. The publication of the second of these created a storm of controversy.

He was interrogated four times by the Inquisition, and in he was forced to recant his views of the heavens. Upon recanting, Galileo was put under house arrest until his death in Isaac Newton was born in the English village of Woolsthorpe. In , when Black Plague closed Cambridge where he was studying, he returned to Woolsthorpe, and there derived his famous three laws of motion.

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These laws of motion were found to work for objects in the heavens, as well as objects on Earth, thereby making Newton the first astrophysicist. His laws of motion are:. Newton distinguished between an object's mass, which is how much matter it contains, and its weight.

A person who is on the moon is attracted by the moon's gravity less than that same person will be attracted to the Earth by Earth's gravity. That person's mass is the same in both places, but the weight is different. Weight is a force, mass is the amount of matter. Newton determined that for the planets to orbit the sun in elliptical trajectories, they must be subject to a force that decreases proportional to the square of their distance from the sun.

In addition, the force must be proportional to the masses of the sun and the planet. In the above formula, F is the mutual force of attraction between the planets, G is the universal gravitational constant, 6. This is the Law of Universal Gravitation because we can extend this equation to any two objects, in the universe.

History of Astronomy Part 1: The Celestial Sphere and Early Observations

Therefore all massive objects are gravitationally attracted to all other massive objects in the universe. The bold idea of a Sun-centered or heliocentric cosmology was also created at this time , but there was not enough evidence to support it and the geocentric picture was chosen by Ptolemy in his summary of Greek astronomy. After the fall of Greek civilization, astronomy made few advances in Europe for over 1, years.

The Copernican revolution was a relatively brief period of dramatic change in human perception, in which humans went from thinking about Earth as the fixed center of the Universe to realizing that Earth is just one of a number of planets moving around the Sun. This change in thinking did not happen overnight, and there was no single observation that overturned the Greek model of the universe.

The History of Astronomy

Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, cosmological, calendrical, and astrological . History of Astronomy: Early Man -> little recorded information on early man's impression of the heavens, some drawings of eclipses, comets, supernovae such as.

The Copernican revolution shows that the progress of science has many twists and turns and even setbacks. It can be dangerous to pursue a new and unpopular idea. Copernicus showed that the complexity and the arbitrariness of Ptolemy's model could be reduced if the Sun were at the center of the planet orbits. The elegance and economy of Copernicus' model were strong points in its favor.

Tycho Brahe then produced a new and accurate set of data on the motions of the planets.

Trace the Earliest History of Astronomy

In Kepler's hands, it was clear that the orbits were better described by ellipses with the Sun at one focus than by circles with the Earth at the center. Kepler also came up with simple relationships that described the orbits in terms of their distance from the Sun.

Galileo made the definitive break with ancient physics. This led to another new idea called the plurality of worlds. This idea holds that there are many planets, that some of them may have properties like Earth, that there may be planets around other stars, even with life forms. These possibilities are strikingly modern — they also relegate the Earth from the center of creation to just one of many astronomical objects.

Isaac Newton transformed the ideas of the Copernican revolution into mathematical laws. These laws of gravity and motion allow the prediction of planet and spacecraft motions. Newton's universal law of gravitation gives a mathematical expression for the force of gravity as an inverse square relation, where the force of gravity drops rapidly with distance from the attracting body.

Newton showed that a falling rock, the Moon in its orbit , and a comet are all governed by the same type of force. By applying Newton's laws of gravity and motion, astronomers can calculate the speeds needed to travel into interplanetary space, launch large telescopes into orbit, and send probes to the Moon and planets.

These probes, in turn, have led to tremendous advances in the understanding of our cosmic environment. Chapter Quiz.