Alta High Astronomy Chapter 2 The History of Astronomy.
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Transcript of Alta High Astronomy Chapter 2 The History of Astronomy.
Alta High Astronomy
Chapter 2
The History of Astronomy
Einstein Einstein improved upon the
work of Newton by explaining how gravity worked!
The Universe is actually made up of a 4 dimensional fabric we call the space-time continuum. Gravity is the effect of heavy massive objects bending or warping that fabric.
Gravity travels at the speed of light 3 x 10 ^8 m/s (186000 mph)
Alta High Astronomy
Alta High Astronomy
The Ancient Astronomers
Most Ancient Astronomy revolved around agriculture Most famous astronomical construct –
Stonehenge on the Salisbury Plain of England Used as a calendar
Other Examples Big Horn Medicine Wheel in Wyoming Caracol Temple on the Yucatan Peninsula
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The Greeks and Muslim Astronomers
Muslim Astronomers Created trigonometry and Algebra – they were the first mathematicians
Greeks – continued their work and developed the first models of the Universe
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The Greeks
The Sun, Moon, and Planets were the known Universe Sun, Moon and Stars were fixed on the Celestial
Sphere Planetes – wanderers planets move both east to
west and appear to move west to east Apparent west to east motion is called retrograde
motion. Aristotle -The Universe is Geocentric –
Everything revolves around the earth and everything moves in a circle.
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Ptolemy
140 AD – Ptolemy constructed the best Geocentric model
In order for the model to fit the data it required the use of epicycles. Epicycles or a circle on a
circle – required over 80 circles The main circle around the
earth is called the deferent and the circle on that circle is called the epicycle
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Copernicus 16th Century – Nicholas Copernicus
rediscovered the early Greek work by Aristarchus which proposed a Heliocentric or “sun centered” universe. This theory was much simpler than
that of Ptolemy – hence it satisfied Occam’s Razor – the philosophy that the simplest solution is usually the best one
Unfortunately this theory contradicted the doctrine of the Catholic Church
Copernicus published this work in Der Revolutionibus – The Revolution meaning the revolution of the planets about the sun. A book that was banned in 1616 by the Church
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Galileo Galilei Also a 16th century astronomer,
Galileo was an italian who first heard of the telescope (no he did not invent it!) and decided to construct one to look at the sky. In 1609 he used his telescope to observe The moon
Had craters and valleys The phases of Venus
Proved it went around the sun 4 moons of Jupiter
Callisto, Ganymede, Io, and Europa
The moons revolved around a planet other than earth
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The Trials of Galileo
1616 – his ideas were declared heretical by the Church
1633 – Placed under house arrest until his death
1992 – Formally Forgiven by the church
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Tycho Brahe
Lived 1546 – 1601 Created the first formal
observatory named Uraniborg on the Island of Hveen in Denmark
Most accurate “naked eye astronomer of his time
Spent more than 20 years charting the known heavens
Hired Johannes Kepler as an assistant to do his mathematical calculations
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Johannes Kepler German Mathematician
– he was not a scientist. He had no theories about the universe he simply wanted a mathematical model to fit the data collected by Brahe.
Hired by Brahe in 1600 he worked for 29 years on the three laws of planetary motion
Kepler’s laws of planetary motion Orbits are elliptical not circular
A planet will sweep out equal areas in equal time.
The time of orbit squared equals the distance to the sun squared ( p2 = a3 )
Alta High Astronomy
Alta High Astronomy
1st Law of Planetary Motion 1st Law Planetary
Orbits are elliptical, not circular Two focal points – sun
is at one foci, every point on the ellipse is the sum of the distances from the foci
Major Axis - length of the long part of the ellipse
Semi-Major Axis - Half the length of the major axis
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2nd Law of Planetary Motion 2nd Law – a planet
sweeps equal areas in equal times This requires planets
to speed up and slow down
Perihelion – When the planet is closest to the sun and moving fastest
Aphelion – When the planet is furthest from the sun and moving slowest
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3rd Law of Planetary Motion
The period of a celestial bodies orbit squared is equivalent to the length of its semi-major axis cubed
Mathematically:p2 = a3
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Sample problem
If Earth is 1 AU from the sun and takes 365 days to go around the sun, how long does it take Mars to orbit the sun if it is 1.5 AUs from the sun?
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Solution
2
2
3
3
m
e
m
e
p
p
a
a
Using the formula:
p2 = a3
Rearrange it for each object
2
3
2
3
m
m
e
e
p
a
p
a 676x
12
3
p
a23
3651
52.1
x
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Eccentricity
Eccentricity – how far off you are from a perfect circle
E = distance between foci/ length of the major axis
Mathematically
E = d/2a
)1( eaP
)1( eaA
APa 2
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Newton
Newton was an English Scientist
He wanted to explain why Kepler’s Laws work
Newton is famous for his three laws of motion which are the basis of Mechanics which is a branch of Physics
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Newton’s Laws of Motion
An object at rest tends to stay at rest, and an object in motion tends to stay in motion. Acceleration is directly proportional to the force applied, and the mass is
inversely proportional to it’s acceleration (F=ma) For every action there is an equal and opposite reaction
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Inertia: A resistance to change, a property of all matter.
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Newton’s Second LawThe Law of Acceleration The acceleration of an object is in the direction of
the force applied. Acceleration is directly proportional to the force
applied. The harder you push an object the faster it goes Acceleration is inversely proportional to the mass of
the object. The heavier the object, the less affect a push has.
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Newton’s Third LawAction - Reaction For every action there is an equal and
opposite Reaction.
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Universal Gravitation
Newton’s Law of Universal Gravitation states that any two objects with mass are attracted to each other
The Force of Attraction is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.
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Universal Gravitation
F = Gm1m2/r2
G – the universal Gravitation constant. Experimentally determined to be
G = 6.67 x 10-11 N•m2/kg2
M1 & M2 – the masses of the objects R2 – the distance between the objects This law explains why an object speeds up when it
is closer to the sun and slows down when it is further away