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Astronomy
In the beginning
Pre-test
True or False:
 1) Greek Astronomers (600BC-150AD)
used telescopes to observe stars.
 Answer: False
 2) What lies at the center of our solar
system?
 A) sun B) Mars C) Earth D) the moon
 Answer: A

Pre-test
What is a rotation?
 A) movement around an object
 B) turning and spinning of a body on it’s
axis
 C) The wobble of a body on it’s axis
 D) WTBW…these are all correct
 Answer: B

Pre-test
What is the approx. rotational period of the
Earth?
 A) 24hrs B) 12hrs C) 30days D) 365days
 Answer: A
 Approx. how long does it take for the
moon to go through all of it’s phases?
 A) 24hrs B) 12hrs C) 30days D) 365days
 Answer: C

WTBW
How old is the Universe?
 How many stars are in the Universe?
 What ancient civilizations contributed to
astronomy?

Introduction

Western astronomy divides into 4 periods

Prehistoric (before 500 B.C.)
 Cyclical
motions of Sun, Moon and stars observed
 Keeping time and determining directions develops
 Classical (500 B.C. to A.D. 1400)
 Measurements of the heavens
 Geometry and models to explain motions

Renaissance (1400 to 1650)
 Accumulation
of data lead to better models
 Technology (the telescope) enters picture

Modern (1650 to present)
 Physical
laws and mathematical techniques
 Technological advances accelerate
History of Astronomy
6
Prehistoric Astronomy

In summary, basis of prehistoric
astronomy:
Rising and setting of Sun, Moon, and stars
 Constellations
 Annual motion of Sun
 Motion of planets through zodiac
 Phases of the Moon
 Eclipses

History of Astronomy
7
The Roots of Astronomy
• Already in the stone (4500-2000BC)
and bronze ages (3600-1700BC),
human cultures realized the cyclic
nature of motions in the sky.
• Evident in hieroglyphics and cuneiforms
• Monuments dating back to ~ 3000 B.C.
show alignments with astronomical
significance.
• Those monuments were probably used
as calendars or even to predict eclipses.
Great Pyramids ~2589-2504BC
Stonehenge
Summer solstice
Heelstone
• Alignments with
locations of sunset,
sunrise, moonset
and moonrise at
summer and winter
solstices
• Probably used as
calendar.
• Constructed: 3000 – 1800 B.C.
Other Examples All Over the World
Big Horn Medicine Wheel (Wyoming)
Other Examples All Over the World (2)
Caracol (Maya culture, approx. A.D. 1000)
Ancient Greek Astronomers
• Unfortunately, there are no written
documents about the significance of
stone and bronze age monuments.
• First preserved written documents
about ancient astronomy are from
ancient Greek philosophy.
• Greeks tried to understand the motions
of the sky and describe them in terms
of mathematical (not physical!) models.
Ancient Greek Astronomers
Models were generally wrong because
they were based on wrong “first
principles”, believed to be “obvious” and
not questioned:
1. Geocentric Universe: Earth at the
Center of the Universe.
2. “Perfect Heavens”: Motions of all
celestial bodies described by motions
involving objects of “perfect” shape, i.e.,
spheres or circles.
Early Ideas of the Heavens

Ancient Greek Astronomers
Through the use of models and observations,
they were the first to use a careful and
systematic manner to explain the workings of
the heavens
 Limited to naked-eye observations, their idea
of using logic and mathematics as tools for
investigating nature is still with us today
 Their investigative methodology is in many
ways as important as the discoveries
themselves

History of Astronomy
17
Eratosthenes (~ 200 B.C.):
Calculation of the Earth’s radius
Angular distance between
Syene and Alexandria:
~ 70
Linear distance between
Syene and Alexandria:
~ 5,000 stadia
Earth Radius ~ 40,000
stadia (probably ~ 14 %
too large) – better than
any previous radius
estimate.
 A value of 25,000 mi. for
the circumference
Early Ideas of the Heavens

The Shape of the Earth
Pythagoras taught as early as 500 B.C. that
the Earth was round, based on the belief that
the sphere is the perfect shape used by the
gods
 By 300 B.C., Aristotle presented naked-eye
observations for the Earth’s spherical shape:

 Shape
of Earth’s shadow on the Moon during an
eclipse
 A traveler moving south will see stars previously
hidden by the southern horizon
History of Astronomy
19
Early Ideas of the Heavens

Distance and Size of the Sun and Moon

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The sizes and distances of the Sun and Moon
relative to Earth were determined by Aristarchus
about 75 years before Eratosthenes measured the
Earth’s size
These relative sizes were based on the angular
size of objects and a simple geometry formula
relating the object’s diameter, its angular size, and
its distance
Aristarchus realizing the Sun was very large
proposed the Sun as center of the Solar System,
but the lack of parallax argued against such a
model
Once the actual size of the Earth was determined,
the absolute sizes and distances of the Sun and
Moon could be determined
History of Astronomy
20
Renissance Astronomy…
Group Project
Presentations
 Sing it  Take a current song or Broadway number
change the lyrics to fit your topic
 Write it  Create a literary piece, a series of sonnets
or ballad that reflects your topic
 Paint it  Take your topic and create a masterpiece
that represents all components of your topic
 Dance it  Interpretive dance that leaves no question
about the interaction in your topic.
 Kid Book  Create a children’s book that tells the
story of your topic through illustrations and word.
 Old Reliable/New Reliable) Tri-fold poster/power
point.
So what is up There…up there,
down there, over there?
Where are we?
 How many stars are out there?
 How many planets are there…really?
 How can we see black holes?
 Is there anything else out there?
 Is there really a “Global Killer”

YOU ARE
HERE.
A sound that was never heard

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The Big Bang Model is a broadly accepted
theory for the origin and evolution of our
universe.
It postulates that 15 billion years ago, the
portion of the universe we can see today was
only a few millimeters across  Singularity
It has since expanded from this hot dense state
into the vast and much cooler cosmos we
currently inhabit.
WTBW
What is the name of the widely accepted
theory about the start of the universe?
 What is the name of the point at which
everything started?
 What ancient civilizations contributed to
modern astronomy?

History of the Big Bang

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In 1927, the Belgian priest Georges Lemaître
was the first to propose that the universe began
with the explosion of a primeval atom.
His proposal came after observing the red shift
in distant nebulas by astronomers to a model of
the universe based on relativity.
Years later, Edwin Hubble found experimental
evidence to help justify Lemaître's theory. He
found that distant galaxies in every direction are
going away from us with speeds proportional to
their distance.
History Continued
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We can see remnants of this hot dense matter
as the now very cold cosmic microwave
background radiation (with high powered
telescopes) which still pervades the universe
and is visible to microwave detectors as a
uniform glow across the entire sky.
Although the Big Bang Theory is widely
accepted, it probably will never be proved;
consequentially, leaving a number of tough,
unanswered questions.
General Theory of Relativity
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The first key idea dates back to 1916 when
Einstein developed his General Theory of
Relativity which he proposed as a new theory of
gravity.
His theory generalizes Isaac Newton's original
theory of gravity, c. 1680, in that it is supposed
to be valid for bodies in motion as well as bodies
at rest.
Newton's gravity is only valid for bodies at rest
or moving very slowly compared to the speed of
light (usually not too restrictive an assumption!).
Relativity

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A key concept of General Relativity is that
gravity is no longer described by a gravitational
"field" but rather it is supposed to be a distortion
of space and time itself.
Physicist John Wheeler put it well when he said
"Matter tells space how to curve, and space tells
matter how to move."
Originally, the theory was able to account for
peculiarities in the orbit of Mercury and the
bending of light by the Sun, both unexplained in
Isaac Newton's theory of gravity. In recent years,
the theory has passed a series of rigorous tests.
WTBW
Who is responsible for the Theory of
Relativity?
 How is gravity explained in the Theory of
Relativity?
 What did the theory of relativity explain?
 What is the distance between the Sun and
Earth?

The Universe

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The Universe is made up of millions of galaxies.
Also out in space is background radiation from
all the explosions and nuclear fusion going on
within stars and nebulae.
The universe has a whole lot of empty space. In
fact, there is so much space even between
single stars in a galaxy that it is difficult to
measure in miles or kilometers.
Space Distance
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Scientists use a distance measurement in space that is
expressed as the distance light will travel in the course of
a year
a light year.
Light travels at a speed of about 186,000 miles per
second.
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That means that light can travel 7.5 times around the entire world
in just 1 second!
In a year's time, light can travel six trillion miles
(6,000,000,000,000).
It takes over 4 years for the light from the nearest star to reach
the Earth (Proxima Centuri)