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Ch. 22: Astronomers

Mr. Litaker

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Our Solar System What do we know?

Time required for Earth to make one rotation on its axis?

24 Hours

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Revolution Time required for Earth to make

one revolution around the sun?

365 ¼ Days

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Time of Year During what time of the year is the

Earth closest to the sun?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?

SummerThe northern hemisphere tilted towards sun resulting in more solar heating

Perihelion

Aphelion

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Orbit

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.

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

Aristotle Ptolemy Copernicus Tycho Brahe Kepler Galileo Newton

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Aristotle 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. Much of our knowledge of Greek

astronomy comes from Claudius Ptolemy.

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 ModelAristarchus – (312-230 B.C.) – (312-230 B.C.) was the 1was the 1stst to believe that the sun to believe that the sun was the center of the universe. was the center of the universe. This was referred to as aThis was referred to as a Heliocentric model.

Everything orbits the sun in this model.

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ViewpointsEven though Aristarchus provided some evidence of distances and sizes that were not completely accurate ---

The Geocentric Model dominated western thought for nearly 2000 years!!!2000 years!!!

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Nicolaus CopernicusCleric and Astronomer1473 - 1543   Finally we shall place the Sun himself at the center of the Universe.All this is suggested by the systematic procession of events andthe harmony of the whole Universe, if only we face the facts,as they say, 'with both eyes open'.   

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Nicolas Copernicus “Copernican Revolution”

Polish astronomer (1473-1543)

Believed that the sun was the center of the solar system.

Heliocentric Model – Sun Centered

The 1st Great

Astronomer

To emerge

In the

Middle Ages!

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Tycho Brahe 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 German astronomer (1571- 1630)

Used the planet data of Tycho Used the planet data of Tycho Brache and developed Brache and developed Kepler’s: Three Laws of Kepler’s: Three Laws of Planetary Motion.Planetary Motion.

Look in the book and copy his 3 laws.

618

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First Law 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 The radius vector describes equal areas

in equal times. (The Second Law)

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.

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 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 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 English Scientist 1643 to 1727

Recognized as the greatest Scientific intellect of all time.

Best known for his laws of motion and universal gravitation formula.

What does the Law of Universal Gravitation state ?

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Play CD:

Discover AstronomySection II

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Earth – Moon Relationships

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Sidereal Day vs. Solar Day 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?

SummerSummer Where is the most direct rays striking?

Tropic of Cancer

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Where does a.m. & p.m.come from

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