Transcript Astronomy

Ch. 22:
Astronomers
Mr. Litaker
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Our Solar System
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What do we know?
Time required for Earth to make
one rotation on its axis?
24 Hours
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Revolution
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Time required for Earth to make
one revolution around the sun?
365 ¼ Days
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Time of Year
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During what time of the year is the
Earth closest to the sun?
Perihelion
Winter
The northern hemisphere tilted away from sun during
winter resulting in less solar heating even though the
earth is closer to sun.
* During what time of the year is the Earth
farthest from the sun?
Aphelion
Summer
The northern hemisphere tilted towards
sun resulting in more solar heating
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Orbit
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What type of orbit does
the Earth have around
the sun?
elliptical
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Early Astronomy
Astronomy – is the science
that studies the universe.
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Astronomy deals with the
properties of objects in
space and the laws under
which the universe
operates.
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Our Solar System
The Historical Perspective
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Aristotle
Ptolemy
Copernicus
Tycho Brahe
Kepler
Galileo
Newton
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Aristotle
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Greek philosopher (384- 322
B.C.)
Believed that the Earth was the
center of the Universe.
Geocentric model – Earth
Centered
** Thought – the Sun, Stars, and
other Planets revolved around the
Earth.
Concluded the Earth was round
because…
It always cast a curved
shadow on the moon.
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Ptolemy 141 A.D.
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Much of our knowledge of Greek
astronomy comes from Claudius
Ptolemy.
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Supported Geocentric Model
Since Ptolemy’s model predicted
motions of the planets, his model
went unchallenged for nearly 13
centuries.
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Heliocentric Model
Aristarchus – (312-230 B.C.)
was the 1st to believe that the sun
was the center of the universe.
This was referred to as a
Heliocentric model.
Everything orbits the sun in this
model.
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Viewpoints
Even though Aristarchus provided
some evidence of distances and
sizes that were not completely
accurate --The Geocentric Model
dominated western thought for
nearly 2000 years!!!
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Nicolaus Copernicus
Cleric and Astronomer
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1473 - 1543
Finally we shall
place the Sun himself
at the center of the
Universe.
All this is suggested by
the systematic
procession of events
and
the harmony of the
whole Universe, if only
we face the facts,
as they say, 'with both
16
eyes open'.
Nicolas Copernicus
“Copernican Revolution”
The 1st
Great
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Astronomer
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To emerge
Polish astronomer (1473-1543)
Believed that the sun was the
center of the solar system.
In the
Middle
Ages!
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Heliocentric Model – Sun
Centered
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Tycho Brahe
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Tycho Brahe Danish Astronomer
(1546 – 1601)
Built an observatory financed by the
king of Denmark.
Made detailed observations and
records of the planets.
Assisted by mathematician Johannes
Kepler
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Johannes Kepler
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German astronomer (1571- 1630)
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Used the planet data of Tycho
Brache and developed
Kepler’s: Three Laws of
Planetary Motion.
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Look in the book and copy his 3
laws.
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First Law
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The First Law:
Planets move in ellipses with the
Sun at one focus.
Circular and Elliptical Orbits Having the Same Period and Focus
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2nd Law
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The radius vector describes equal areas
in equal times. (The Second Law)
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For a circle the motion is uniform as shown
above, but in order for an object along an
elliptical orbit to sweep out the area at a
uniform rate, the object moves quickly when
the radius vector is short and the object
moves slowly when the radius vector is long.
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3rd Law
The Third Law:
The squares of the periodic times are to
each other as the cubes of the mean
distances.
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This law he published in 1619 in his
Harmonices Mundi . It was this law,
not an apple, that lead Newton to his
law of gravitation. Kepler can truly be
called the founder of celestial
mechanics.
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Galileo Galilei
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Galileo Galilei
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Italian Mathematician (1564 –
1642)
Invented the telescope in 1608 and
observed… ?
Look in the book on page 619 and
list the 5 discoveries Galileo made
with his telescope.
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Galileo
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Galileo quickly discovered that our Moon had
craters, that Jupiter had it's own moons, that
the Sun has spots, and that Venus has phases
like our Moon. Galileo, who lived from 1564 to
1642, made many more discoveries. Galileo
claimed that his observations only made sense
if all the planets revolved around the Sun, as
championed by Aristarchus and Copernicus,
not the Earth, as was commonly believed then.
The powerful Inquisition made Galileo publicly
recant this conclusion, but today we know he
was correct.
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Newton
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Isaac Newton
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English Scientist 1643 to 1727
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Recognized as the greatest Scientific
intellect of all time.
Best known for his laws of motion and
universal gravitation formula.
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What does the
Law of Universal Gravitation state ?
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Play CD:
Discover Astronomy
Section II
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Earth – Moon Relationships
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Sidereal Day vs. Solar Day
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Solar Day – 24 Rotation using the
Sun as our reference.
Sidereal Day – 23 hours 56
minutes for one complete rotation
using a star other than the sun.
There is a loss of 4 minutes or 10.
Power Line Example: At Night
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What season is the
Northern Hemisphere
experiencing?
Summer
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Where is the
most direct
rays striking?
Tropic of Cancer39
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Where does a.m. & p.m.come from
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