1. History of Astronomy DAY TWO

2. Polaris – The North Star  “The North Star or Pole Star – aka Polaris – is famous for holding nearly still in our sky while the entire northern sky moves around it. That’s because it’s located nearly at the north celestial pole.”  “Polaris marks the way due north.”

3.  Circumpolar – visible all year long (go around Polaris without ever rising or setting)

4. Precession : rotation of Earth’s axis itself; makes one complete circle in about 26,000 years; causes us to ‘wobble’ Terminology…

5. Observations known to the ancients…  Appears like we are inside a dome Celestial Sphere:

6. Observations known to the ancients…  Half of the Celestial Sphere is above the horizon  (what we see)  Half of the Celestial Sphere is below the horizon  (what we can’t see)

7. Observations known to the ancients…  The Celestial Sphere moves  Stars appear to move together (Stars are “fixed” on the Celestial Sphere)

8. Observations known to the ancients…  The Moon is not fixed on the Celestial Sphere  It rises and sets  The Sun is not fixed on the Celestial Sphere  It rises and sets  The planets are not fixed on the Celestial Sphere (the term “Planet” actually means, wandering star.)

9. Observations of the ancients… The Greeks made observations of the night sky Regardless of whether their inferences were right or wrong, the Greeks start to compile theories about the “Universe”

10. Passage of astronomical knowledgeAncientBabylon AncientEgypt AncientGreece Ancient Roman Empire

11. Greeks Before we get into details, you have to know that Religion played a huge role in Greek Society. (And we’ll see that religion will be a big factor for a long time after as well)

12. Ancient Greeks & MOTION 1. Natural motion  Every body in the universe had a proper place, determined by its “nature”; and would “strive” to get ther  Larger bodies were thought to “strive” harder (Fall Faster)  Up and down motion – as in the case of all things on Earth  Circular motion – as in the case of celestial objects

13. Ancient Greeks & MOTION 2. Violent motion (force)  Imposed motion  Resulted from pushing or pulling

14. Ancient Greeks & MOTION Summary:  All motions resulted either from the nature of the moving object or from a sustained push or pull.  Except for the celestial bodies, the normal state was one of rest.

15. Religious Significance:  Their astronomical views were intertwined with their religious beliefs  Greeks believed that their “God(s)” placed them at the center of the Universe So…  They developed models and theories of the Universe that placed Earth at the center (geocentric).