History of Astronomy

• Astronomy is the oldest of the sciences.

• Stonehenge, constructed between 3100-2000 BCE on England's Salisbury Plain, may have been used to keep track of the solar-lunar eclipse cycle.

Some Chinese people kept careful track of events in the skies, particularly the appearance of "guest stars" -- comets, novae and other transients such as Comet Halley whose observation can be traced back to 240 BCE and possibly as early as 1059 BCE.A progress in the field of Astronomy has occurred starting from Greek natural philosophers, scientists and mathematicians as Pythagoras of Samos, Aristotle, Eratosthenes of Cyrene.

(85-165) He was a mathematician, geographer, and astronomer who developed the most sophisticated mathematical model of the motions of the Solar System based upon the geocentric (Earth-centered) model and the principle of perfect circular motion.

He expressed his ideas

in a treatise, The Almagest

Claudius Ptolemy

•The celestial realm is spherical, and moves as a sphere. •The earth is a sphere. •The earth is at the center of the cosmos. •The earth, in relation to the distance of the fixed stars, has no appreciable size and must be treated as a mathematical point. •The earth does not move.

Ptolemy’s cosmos

Ptolemy assigned the following order to theplanetary spheres beginning with the innermost:

1.Moon 2.Mercury 3.Venus 4.Sun 5.Mars 6. Jupiter 7.Saturn 8.Sphere of fixed stars

Nikolas Kopernig (1473-1543) developed a heliocentric model of the Solar System which placed the Sun at the center and established the proper order of the planets outward from it.

Nikolas Kopernig

In a book called On the Revolutions of the Heavenly Bodies (that was published as Copernicus lay on his deathbed), Copernicus proposed that the Sun, not the Earth, was the center of the Solar System.

Such a model is called a heliocentric system. The ordering of the planets known to Copernicus in this new system is illustrated in the following figure, which we recognize as the modern ordering of those planets.

Tyge (Tyco) Brahe developed his own Solar System model in which the Sun orbits the Earth, but the remaining planets orbit the Sun. Tycho Brahe's contributions to astronomy were enormous. He not only designed and built instruments, he also calibrated them and checked their accuracy periodically. He thus revolutionized astronomical instrumentation. He also changed observational practice profoundly. Whereas earlier astronomers had been content to observe the positions of planets and the Moon at certain important points of their orbits

Tyge Brahe

Galileo Galilei

Galileo Galilei (1564-1642) was the first "modern scientist" who argued that mathematics is the true language of science. He performed many revolutionary experiments in mechanics and other fields of physics.

Johannes Kepler (1571-1630) developed three mathematical rules for the orbits of the planets:

The orbits of the planets are ellipses with the Sun at one focus.

The planets sweep out equal areas during equal times of the orbit.

The square of the orbital period is proportional to the cube of the planet's distance from the Sun. (If you measure the period in Earth years and the distance in Astronomical Units (1 A.U.= the average distance of the Earth from the Sun), then Period2 = Distance 3.)

Johannes Kepler

Isaac Newton (1642-1727) developed the science of mechanics as we know it. His first development was his Laws Of Motion. To perform mechanical calculations and to understand Gravity, Newton invented a mathematical tool that he called "fluctions", now known as “calculus”. http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/The_rise_of_calculus.html

Isaac Newton

Edmund Halley (1656-1742) made an analysis of what is now known as Halley's comet is a perfect example of the scientific method in action. He observed that the comets of 1456, 1531, 1607, and 1682 followed similar orbital paths around the Sun and that each appearance was separated from the previous one by about 76 years -- which was the period predicted for the orbit by Kepler's Third Law. He predicted that the comet would return again in 1758. The comet was sighted, on schedule, on Christmas Day 1758 and has taken Halley's name.

Edmund Halley

Albert Einstein (1879-1955) revolutionized all aspects of science and modern thought through his theories of general and special relativity and idea of equivalence.

Albert Einstein

The origin of the Solar System

• http://www.youtube.com/watch?v=_pkz_x4YNr8