History of

1
History of Astronomy
2
The First Astronomers

• It is likely that the first astronomers were
  simply curious people who noticed patterns in the
  night sky.
• More advanced observers even noticed seasonal
  trends to where and when these patterns appeared.

3
Modeling the Universe

• Early Greeks made more advanced observations,
  noting that some of the objects in the sky moved
  in relation to the stars. These were called
  planets from the root Greek word for wanderer.

Mars motion plotted against the stars
4
Modeling the Universe

• The Greeks made the first recorded attempt at a
  model of what the solar system looked like.
• All our senses tell us that the Earth is not
  moving so the first model placed Earth at the
  center with planets and sun rotating around it
  the geocentric model (earth centered).

5
The Earth is a Sphere

• A man named Eratosthenes ( 200B.C.) notices a
  strange phenomena with shadows in different
  cities and uses it to calculate the radius of the
  Earth.

Shadow behind post
No Shadow in well
6
Geocentric Model Challenged

• Observations of the planets reveal irregular
  movement of some planets pointing to a problem in
  the earth-centered (geocentric) model of the
  solar system.
• As long ago as 250 B.C. some began to think
  that the Sun may be at the center of the solar
  system.

?
7
Geocentric Model Fights

• Mainly based on a lack of evidence for Earths
  movement, the idea that the Earth is the center
  of the universe remains accepted for about 1500
  years until the 1500s.

8
Evidence Wins the Fight

• More and more problems develop when the
  earth-centered (geocentric) model is studied.
• In the late 1400s, Nicholas Copernicus proposes
  the Sun-centered (heliocentric) model of the
  universe essentially the current model.
• This model, though not quickly accepted by
  people, explained the erratic motions of the
  planets in a simple easy way.
• If a new model is better supported by the
  evidence, the old must be thrown out.

9
Supporting the Model

• In addition to his explanations for moving
  objects In the late 1500s Galileo builds (not
  invents) a telescope to look at the planets and
  stars.
• His observations support the heliocentric model.

10
Heliocentric Model is Refined

• In the early 1600s, A man named Johannes Kepler,
  studies the observations of another man (Tycho
  Brahe) and comes up with 3 laws of planetary
  motion.
• The easiest to understand being that the planets
  orbit the sun (heliocentric) but they orbit in
  ellipses not perfect circles.

An ellipse can be drawn with this method
11
Explaining the Forces in the Heavens

• In the late 1600s, Isaac Newton describes why
  planets move in elliptical paths around the Sun.
• GRAVITY a force that causes all masses to
  attract other masses pulls the moving bodies
  inward.
• Opposing gravity is the moving objects tendency
  to move in a straight line (inertia).
• The two forces balance and the planets move in
  near circular (elliptical) paths around the most
  massive body the Sun.

12
Beyond that

• Modern technology such as the Hubble space
  telescope, radio telescopes, and the work of
  scientists like Einstein, Hubble, etc have lead
  to a wealth of understanding.
• Currently, the model of the solar system is
  essentially the heliocentric model already
  explained.
• However, the universe consists of countless
  suns (stars) organized in a countless number of
  galaxies
• Makes your head hurt to think about infinity or
  forever ouch.