Transcript Historical pursuit of the "heavens"

The First Astronomers
• It is likely that the first astronomers were
simply curious people who:
– imagined how big this dirt place we stand on
is and what shape it would be.
– looked up to noticed patterns in the night sky.
– even noticed seasonal trends to where and
when these patterns appeared.
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…
Modeling the Universe
• The Greeks made the first recorded
attempt at a “model” of what they saw.
• 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).
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
Geocentric Model Challenged
• Observations of the planets (mostly Mars)
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.
Geocentric Model Fights
• Mainly based on a lack of evidence for
Earth’s movement, the idea that the Earth
is the center of the universe remains
accepted for about 1500 years… until the
1500’s.
Evidence Wins the Fight
• More and more problems develop when the
earth-centered (geocentric) model is studied.
• In the late 1400’s, 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.
Supporting the Model
• In addition to his explanations for moving
objects; In the late 1500’s Galileo builds (not
invents) a telescope to look at the planets and
stars.
• His observations support the heliocentric model.
Heliocentric Model is Refined
• In the early 1600’s, 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
Explaining the Forces in the Heavens
• In the late 1600’s, 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 object’s
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.
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.