History of AstronomyDAY TWO

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.”

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

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

Terminology…

Observations known to the ancients…Appears like we are inside a dome

Celestial Sphere:

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)

Observations known to the ancients…

The Celestial Sphere movesStars appear to move together

(Stars are “fixed” on the Celestial Sphere)

Observations known to the ancients…

The Moon is not fixed on the Celestial SphereIt rises and sets

The Sun is not fixed on the Celestial SphereIt rises and sets

The planets are not fixed on the Celestial Sphere (the term “Planet” actually means, wandering star.)

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”

Passage of astronomical knowledge Ancient

Babylon

AncientEgypt

AncientGreeceAncient Roman

Empire

GreeksBefore 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)

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

Ancient Greeks & MOTION

2. Violent motion (force)

Imposed motion

Resulted from pushing or pulling

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.

Religious Significance:Their astronomical views were intertwined with their religious

beliefs Greeks believed that their “God(s)” placed them at the center of

the UniverseSo…They developed models and theories of the Universe that placed

Earth at the center (geocentric).