Ancient Evenings: The First Watches

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Chapter 2 Ancient Evenings The First Watches
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As early as 3000 BC, people have charted the
heavens. (Babylonians)
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The Chinese gave us the 365-day calendar over
4500 years ago.
An eclipse when one celestial body passes in
front of another.
A conjunction is when two (or more) celestial
objects are close to one another.
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The Venus tablets gave people the motivation to
further study and record the events of the night
sky.
Not this Venus
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The Egyptians charted the stars in order to help
their dead find their way. In doing so, they
created a working calendar.
The Egyptian calendar found year to be 365.25
days long. (Very accurate!)
Circumpolar stars are those that close to
Polaris. They stay in our sky all year long.
Leap Year!
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Egyptian
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Stonehenge
Stonehenge was built in England from about 2800
B.C. to 1550 B.C.
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The sun and moon align with certain stones during
notable times of the year Summer and winter
solstices Vernal and autumnal equinoxes -more
about these later.
Many structures around the world have been built
to do this very same thing.
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The Greeks!
The ancient Greeks are the first to use
astronomical observations to explain the physical
realities of our world.
Philosopher Lover of Wisdom.
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Anaximander 570 BC
The founder of astronomy, he believed the
entire universe was made of apeiron.
He also felt that the Earth floated freely in
space at the center of the universe
and the sun was a chariot wheel of fire.
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Anaximenes 545 B.C.
He was the first person to have said the stars
and the sun) burn.
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Pythagoras 550 B.C.
Stated 1)The Earth is a sphere, fixed within the
celestial sphere.
2) The planets and the sun moved relative to the
stars.
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Anaxagoras 460 B.C.
Explained the Sun, Earth and moon system and the
role the play in eclipses.
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Aristarchus 280 B.C.
Stated the Earth revolved around the sun while
spinning on its axis. (Geocentric Model)
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Eratosthenes 240 B.C.(Not in your book)
Noticed 1) The suns rays strike the earth at
different places at different angles.
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2) Calculated the size of the earth using angles
of incoming solar light.
He was only off by 4!
3) He accurately measured the tilt of the earth
on its axis.
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Eratosthenes also compiled a star catalog and a
calendar that included a leap year.
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Aristotle (360 B.C.) placed Earth at the center
(geocentric) and all bodies orbited us in perfect
circles.
The church liked that idea, but it failed to
explain planetary motion.
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Ptolemy (130 C.E.) added epicycles to
Aristotles idea.
This new idea explained so much (even though it
was totally wrong), that people believed it for
over 14 centuries!
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Two Arabs
In the year 820, Ptolemys book was translated
into Arabic.
There, it was known as Almagest (The Great Book).
Here, astronomy was reborn.
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Al-Battani (880)
He published the book, On Stellar Motion.
Al-Battani also refined earlier measurements with
the use of trigonometry rather than geometry.
He also proved the suns apogee varies.
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He wrote, Writings of the Celestial Muse.
Al-Sufi also compared the brightness of stars,
created catalogs, and influenced the names of
many stars and common astronomical terms.
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Nicholas Copernicus
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Copernicus (1590) was a brilliant Polish
astronomer who found many errors in Ptolemys
ideas.
He found Ptolemys model too complex.
The more simple the model, the more pleasing to
the mind.
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In 1514, Copernicus revisited the idea of the
heliocentric (heliostatic) model.
A 2000 year-old idea of Aristarchus.
In 1543, he published his ideas, but was not 100
correctthe idea of circular orbits kept getting
in the way.
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In rethinking the motions of the planets
1) The stars must be VERY far awaymeaning the
universe must be gigantic!
Otherwise, as the earth orbits the sun, they
would appear to get brighter, then dimmer.
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2) What makes things fall???
And, oh yeahman is NOT at the center of the
universe!
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Tycho Brahe (Bra-Hey) 1580
Inspired as a young boy, he devoted his life to
the careful observation of the sky.
King Frederick II of Denmark built him an
observatory where he made meticulous observations.
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Johannes Kepler 1600
Became an apprentice to Brahe in 1600.
After Brahes death in 1601, Kepler inherits all
of his data.
He wanted to take this information and explain
the heliocentric idea more accurately.
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His ideas revolve around ellipses, not circles
Keplers three laws
1st The planets orbit the sun in elliptical
paths with the sun being one of the foci.
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2nd The law of equal areas.
(The time frame for each dot is equal)
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3rd Period vs. axis
The square of the planets orbital period (year)
is proportional to the cube of its semi-major
axis.
P2 a3
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Galileo (1610)
With his telescope, he observed recorded many
objects and occurrences.
It was his observations of Venus that led him to
conclude that our world is heliocentric.
By order of the Catholic church, he was sentenced
to house arrest in 1633.
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Issac Newton (1680)
A brilliant English mathematician puts it all
together in The Principia.
Newton did so with his 3 laws of motion and his
ideas of gravity.
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Newtons first lawInertia.
An object at rest tends to stay at rest and an
object in motion tends to stay in motion with the
same speed and in the same direction unless acted
upon by an unbalanced force.
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Newtons 2nd lawFMA
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Newtons 3rd lawaction/reaction.
According to Newton's third law, for every action
force there is an equal (in size) and opposite
(in direction) reaction force. Forces always come
in pairs - known as "action-reaction force
pairs."
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Gravitational force of attraction is universal.
Gravity is proportional to the mass of the bodies
and it weakens as to the square of the distance
between them.
Newtons work explained all observations as well
as confirmed by all predictions.
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For all of his work and contributions to science,
Isaac Newton is known as The greatest mind in
the history of human thought.