HISTORY OF ASTRONOMY CONTD.

2.5 Nicolus Copernicus ( )  Heliocentric model.  Circular orbits.  Explanation of the retrograde motion of planets.  Explained why Mercury & Venus are always close to the sun.  No observational way to distinguish between geocentric model and heliocentric model.

Problems with the Heliocentric Model  The changing speeds of the Sun, Moon, and planets is not explained.  We do not feel the Earth moving or the atmosphere being pulled away as we fly around the Sun.  If the Earth were spinning, wouldn’t we be thrown off into space?  Why is there no parallax due to our spin or our orbit?

2.6 Tycho Brahe ( )  Built instruments of high accuracy.  Studied the planetary positions.  He gathered a huge amount of data about planets motions, positions, orbits.

Kepler  Kepler worked as an assistant for 10 monthes.  He used the data of Tycho to:  reveal the true shape of planetary orbits  the relation between the orbit radius and the period.

Foucault Pendulum, Pantheon - Paris (1851)  a tall pendulum free to oscillate in any vertical plane. The direction along which the pendulum swings appears to rotate with time because of Earth's daily rotation. This is because the plane of the pendulum's swing, it tends to keep a fixed direction in space, while the Earth rotates under it.

Foucault Pendulum  the angular speed, α (measured in clockwise degrees per day), is proportional to the sine of the latitude, φ :

2.7a Stonehenge

2.7b Newgrange & Knowth

2.7c Mayan Astronomy  Agricultural calendar  Studied Venus’s motion  Monuments pointing to the Sun And Venus on significant days.

2.7d Native American Astronomy  50 Bighorn Medicine Wheels  Alligned to astronomical directions.

Measuring the Diameter of the Moon  Aristarchus أرستارخوس

Measuring the distance to the Moon  How ?  Try it yourself !