Astronomy HISTORY OF ASTRONOMY

The scientific method had not been invented yet Most of the ideas of the time were based on Pure Thought The ideas of Greek philosophers dominated for over 1500 years

The heavens are perfect and unchanging Geocentric Model – Earth is the center of the Universe Planets and stars are perfect crystalline spheres rotating around Earth –Ancient Greeks needed to study the sky for Agriculture & Navigation Parallax – the apparent shift of an intermediate object w/ respect to the background with shift in change of the observer Plato and Aristotle (384 – 322 BC)

Aristotle saw no parallax = Earth must be stationary

 Similar to Aristotle, but also explained retrograde motion  Retrograde – the planet goes back & loops around back to prograde (forward) motion. Ptolemy, an Egyptian Pharaoh

The Ptolemaic Cycle

 The Ptolemaic Cycle – Epicycle & deferent  Mercury, Venus, Sun move together around Earth on epicycles  Planets move in epicycles, which move around deferents centered on the equant

Nicholas Copernicus Heliocentric Model – The Sun is at the center of the Universe Stars & planets revolve around the Sun in perfect circles Still need epicycles! NOT based on scientific evidence – based on literature

Tycho Brahe Passion for accuracy and for consulting the sky (rather than ancient authority) Made decades of detailed, excruciating precise measurements of planetary positions 1572: Tycho’s supernova - heavens are not fixed – they changed!

Johannes Kepler Inherited Tycho’s observations Three Laws of Planetary Motion First mathematical description of planetary motion Orbits of planets are Elliptical

Ellipse – a conic section not parallel to the base

Law 1:The shape of the orbit Law 2:How fast the planet moves at each point in its orbit Law 3:How long the planet takes to complete one orbit Kepler’s Laws Earth’s ellipse – foci are inside the sun It’s almost a circle. Laws were empirical: He adjusted the theory to fit the data – problem was – He didn’t know WHY it worked…

Galileo Galilei  First astronomical use of the telescope  5 Major Observations of the heavens 1.Moon has mountains, valleys, craters (it’s not perfect) 2.Sun is not perfect or unchanging it has sunspots 3.A host of stars too faint to be seen with the naked eye suggested that the sky has depth 4.Jupiter has 4 moons – everything does not revolve around Earth 5.Phases of Venus – like the Moon  Support for the Heliocentric Model

Galileo’s 5 Observations 1.Moon has mountains, valleys, craters (it’s not perfect) 2.Sun is not perfect or unchanging it has sunspots 3.A host of stars too faint to be seen with the naked eye suggested that the sky has depth

4. The 4 moons of Jupiter

5. Phases of Venus

Phases of Venus (con’t)

Sir Isaac Newton (1642 – 1727)  Reflecting telescope  “Newtonian”  Splitting of light into its component colors “spectra”  Invented the Scientific Method  3 Laws of Motion

Newton’s First Law of Motion Law of Inertia An object at rest tends to stay at rest, And an object in motion tends to stay in motion.

Newton’s Second Law of Motion If the same force is exerted on two objects of different mass, you will get different accelerations (changes in motion)

Newton’s Third Law of Motion Action- Reaction Pairs For every action (force) there is an equal and opposite reaction (force). Forces are found in pairs.

Newton’s Universal Law of Gravity Any two objects attract each other with a force that is related to their gravities, masses and the distance between them.