Lecture 3Ancient astronomy Aristarchus, Ptolemy

Modern astronomyCopernicus, Tycho, Galileo, Kepler, NewtonCircular satellite motion and tide

LightSpeed of light, Nature of light, EM radiation, Relation to temperature, Black body radiation, Wien’s law, SB law, Planck’s law, Kirchoff’s law, Bohr model, Doppler effect

By reading this chapter, you will learn4-1 How ancient astronomers

attempted to explain the motions of the planets

4-2 What led Copernicus to a Sun-centered model of planetary motion

4-3 How Tycho’s naked-eye observations of the sky revolutionized ideas about the heavens

4-4 How Kepler deduced the shapes of the orbits of the planets

4-5 How Galileo’s pioneering observations with a telescope supported a Sun-centered model

4-6 The ideas behind Newton’s laws, which govern the motion of all physical objects, including the planets

4-7 Why planets stay in their orbits and don’t fall into the Sun

4-8 What causes ocean tides on Earth

Ancient astronomy

• Around 200 B.C., the Greek astronomer Eratosthenes made the first reasonable measurement of size of the Earth

• Solar eclipse: distance between Earth&Moon must be smaller than Earth&Sun: Not all celestial objects are at equi-distance.

• Phases of the moon: the moon must be a sphere!

• Aristotle( 384-322BCE) concluded from observations of the curved shadow of the Earth on the Moon during a lunar eclipse that the Earth was spherical.

• In addition, he noticed that stars were visible in some southern locations, while not visible in northern locations. Again, the Earth must be spherical for this to happen!

•Aristarchus used the triangulation, he calculated the distances to the Sun and Moon

Geocentric model

Earth

Planet

Deferent

Epicycle

Change the fixed object to investigate the apparent motion of the planets. Fix the blue object to see how superior planets appear to move. Fix the red object to see how inferior planets appear to move.

Any questions on ancient astronomy?

1. Who was the first person to measure the size ( circumference) of the Earth? A) Pythagoras, b) Aristotle, c) Aristarchus, d) Eratosthenes, e) Ptolemy

2. The concept of the Universe adopted by most ancient Greek philosophers was (a)Earth-centered, with Sun, Moon, planets and the stars orbiting around a stationary Earth. (b)Sun-centered, with Earth, Moon, planets and the stars orbiting around a stationary Sun. (c)stationary, the fixed Sun, Moon, planets and the stars appearing to move when viewed from a rotating Earth.

3. Epicycles are used in a geocentric model to explain the a) eastward motion of Mars. b) westward motion of Mars. c) phases of Venus.d) appearance of Venus in the early morning or late evening sky.

4. What model did ancient astronomers use to explain the motions of the planets?