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Definition
• Seafarers needed to navigate their vessels
• Farmers had to know when to plant their crops
• The The need to predict the arri al of seasons need to predict the arrival of seasons Æ Calendars
• Religion |
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The study of the ancient astronomical sites which
have left us with no written records or names of the
people who set up the ruins that we study today. |
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| Megalithic Site –Circle of stones marking solstices and cardinal points more than 6000 years ago in Southern Egypt. |
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Salisbury Plain in England. Many stones are aligned pointing towards important astronomical events. Very
accurate alignments. It is the most impressive and best perserved. |
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| Wyoming, built by the Plain Indians. Its spokes are aligned with rising an settings of the sun and other stars. |
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| Mayans in Mexico. Windows aligned with astronomical events, keeping track of the seasons and heavens. Also used for human sacrifices. |
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Differs from Archaeoastronomy, because it is documented, written record of events. It is reasoned out theories of how thing worked.
It is experimental with data and observations. |
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Definition
Solar System: Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn.
The stars beyond were fixed on the celestial sphere |
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Term
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Definition
Length Length of the year to a high precision of the year to a high precision
The The earth is round earth is round
Diameter Diameter of the earth/distance to the moon of the earth/distance to the moon.
Two models for the Solar System
• Heliocentric Heliocentric (Sun at the centre)
• Geocentric Geocentric (Earth at the center) |
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Term
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Definition
Length Length of the year to a high precision of the year to a high precision
The The earth is round earth is round
Diameter Diameter of the earth/distance to the moon of the earth/distance to the moon.
Two models for the Solar System
• Heliocentric Heliocentric (Sun at the centre)
• Geocentric Geocentric (Earth at the center) |
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Term
The geocentric universe:
earliest model of the Solar System |
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Definition
| Greek astronomers observed that all the planets move within 7 degrees of the ecliptic. So the Solar System is quite flat when viewed along the ecliptic plane. |
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Stars slide smoothly across the sky. The Sun and the Moon
progresses along the ecliptic at an almost constant rate. |
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Definition
Earth lays at the centre of the Universe and all other
bodies moved around it, in circular and uniform orbits. |
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Term
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| derives from the Greek word planetes, meaning “wanderer” |
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Bakcward loops
Planets appear brightest during the retrograde portion portion of their of their orbits. |
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Definition
Could not account for observed variations in
planetary brightness
retrograde motion
Solution: Planets move on small circles called epicycles, whose centers orbited Earth on larger circles called deferents. |
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Ptolemy produced the most complete geocentric model of
all times ----> Ptolemaic model |
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Definition
The full Ptolemaic model required a series of no fewer
than 80 circles to explain the observable Universe
Ptolemaic model survived for almost 14 centuries, until the
16th century. |
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Term
| The Heliocentric Model of the Universe |
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Definition
Copernicus rediscovered the heliocentric model.
-Earth is not at the center of the universe but, like other
planets, orbits the Sun “in circular orbits”.
-Earth Spins on its axis.
Explains:
1- The daily and seasonal changes in the heavens
2- Retrograde motion of the planets
3- Brightness of the planets |
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Heliocentric Model
Advantages and Disadvantages |
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Definition
Advantage: simplicity
Disadvantage: contradicted the doctrine of the Roman Catholic church
His ideas were never accepted during his lifetime. |
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Italian mathematician an philosopher, was
the father of experimental science. |
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The Moon had mountains, valleys, and craters.
- The Sun had imperfections
(sunspots) and rotates.
- Jupiter Jupiter satellites (moons) satellites (moons).
- Phases of Venus confirming the heliocentric model. |
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Definition
He was imprisoned in 1633 until the end of his life
because of his heretical ideas.
Not until 1992 did the Church publicly forgive Galileo's “crimes” |
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Definition
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Term
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Definition
(1571-1630), a German mathematician and
astronomer, was a pure theorist. |
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Definition
He based work about planetary motion on the detailed observations of the astronomer astronomer Tycho Brahe.
Tycho made observations with instruments
of his own design.
Kepler summarized Tycho's observation data in his three laws of planetary motion. |
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Term
| Three Laws of Planetary Motion |
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Definition
1-The orbital paths of the planets are elliptical, with the Sun
at one focus.
2-An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time.
3-The square of a planet orbital period is proportional to
the cube of its semi-major axis |
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Definition
the ratio of the distance between the foci
(plural of focus) to the length of the major axis ---> how flattened it is.
Planetary Planetary orbits have very small eccentricity (except Mercury)
Comets have very large eccentricity |
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Definition
| time needed to complete one circuit around the Sun |
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• the shapes of the planet orbits
• the the relative sizes of all the planetary relative sizes of all the planetaryorbits with respect to Earth orbit
• the speeds at which they move
To obtain the actual size of the orbits we need to now a distance into the Solar System ---> distance Earth-Venus using parallax from different points on Earth.
More precise measurement has been made
using radar (accuracy of about 1 km) |
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Term
| The measurement of distance: Parallax |
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Definition
• Knowing the baseline (the distance between the two observation p ) points) and the parallax angle it is possible to
determine the distance just using Euclidean geometry.
• The larger the baseline, the larger the
parallax.
• The further the object, the smaller the parallax. |
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Term
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Definition
| Newton's answer was that a fundamental force called “gravity” operating between all objects made them move the way they do. |
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Term
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Definition
Unless some external force changes its state of motion, an object at rest remains a moving object continues
to move forever in a straight line with constant
speed. |
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Term
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Definition
Acceleration: The rate of change of velocity of a moving object.
The acceleration of an object is directly proportional to the
applied force and inversely proportional to the object mass. |
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Term
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Definition
Forces cannot occur in isolation:
to every action, there is an equal
and opposite reaction. |
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Term
| Newtons Thoughts on Gravity |
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Definition
To explain planetary orbits Newton postulated that
gravity gravity attracts the planets to the Sun
The more massive the obj , ject, the
stronger its gravitational pull. |
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Term
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Definition
The strength of the Sun g p gravitational pull decreases in
proportion to the square of the distance from the Sun. |
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Term
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Definition
| A stable orbit is the net result of the the combination of gravity and inertia. |
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Term
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Definition
Orbits of two bodies with equal masses. Identical
ellipses with a common focus at the centre of mass.
Orbits of two bodies with one body twice as massive
as the other. Common focus but more massive body
moves more slowly and in a smaller orbit (half size).
Planet orbiting the Sun. The common focus of the two
orbits lies inside the Sun. |
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