Transcript Eratosthenes

EARTH’S, FORMATION SHAPE,
DIMENSIONS AND HEAT
CHAPTER 4.1
Earth’s Origin
Observe an animation showing the origin of the solar system.
Earth’s Size and Shape
HISTORICAL EVIDENCE OF
SHAPE
1.
2.
3.
4.
5.
SHIPS MAST
CHANGING POSITIONS OF
CONSTELLATIONS
EARTHS ARC DURING ECLIPSE
GRAVITATION – OBJECTS WEIGH
NEARLY THE SAME
MAGELLAN’S CIRCUMNAVIGATION
The Earth’s shape is an Oblate
Spheroid
OBLATE SPHEROID – TRUE SHAPE OF EARTH. SLIGHTLY
FLATTENED AT THE POLES (40,007 KM) BULGING AT THE
EQUATOR (40,074 KM). OBJECTS AT THE POLES WEIGH
MORE THAN AT THE EQUATOR!
Eratosthenes
• (276 - 195 B.C.)
Eratosthenes

Greek scholar
 called the "father of geography“
 educated at the academies of Athens
 Appointed
to run the Great Library at Alexandria
in 240.
He served as the director of the famous library in
Alexandria.
ERATOSTHENES – FIRST SCIENTIFIC MEASUREMENT OF
THE CIRCUMFERENCE OF THE EARTH.
TWO REQUIREMENTS:
1. ANGULAR DIFFERENCE FROM SYENE TO
ALEXANDRIA
2. SURFACE DISTANCE BETWEEN TWO
CITIES(DIRECTLY NORTH)
• Having discovered in his reading that a deep well at Syene (near
the Tropic of Cancer and modern Aswan) where sunlight only
struck the bottom of the well on the summer solstice,
Eratosthenes determined that he could discover the
circumference of the earth.
•Eratosthenes measured the altitude of the noontime sun at
Alexandria at its maximum on Jun 21st.
• Erastosthenes also calculated the tilt of earths axis
Analema

a trace of the annual movement of the
Sun on the sky

Due to the earth's tilt on its axis (23.45°) and its
elliptical orbit around the sun, the relative location of the
sun above the horizon is not constant from day to day
when observed at the same time on each day.
Depending on one's geographical latitude, this loop will
be inclined at different angles
Earth is misnamed!
Should be called ocean
(71%) and land (29%)
Earth’s Interior
Layers of Earth
Inner core – solid iron and nickle
Outer core – liquid iron and nickle
Mantle – thickest layer, iron, silicon and
magnesium compounds – behaves as a liquid
Asthenosphere – slush-like layer of mantle
crust floats on
Crust – Thin layer of rigid lighter rock that
includes earth’s surface
Lithosphere – Crust and uppermost part of
mantle
SPECIFIC GRAVITY
Weight of an object compared to the
weight of an equal volume of water.
Useful in mineral identification!
Earth’s avg. density is 5.5
Crust = 2.8
FORMULA
S.G
=
Wa
Wa – WH20
Wa = WEIGHT IN AIR
WH20 = WEIGHT IN WATER
Earth’s Heat
TEMPERATURE
• 70 METERS DEPTH CONSTANT AND
EQUAL TO AVG. YEARLY TEMP OF THAT
LOCATION
•TEMP IN CRUST RISES 10/40 METERS IN
DEPTH
•12,800 KM DIAMETER
•6400 KM RADIUS X 1000 M/KM DIVIDED
BY 40 = 160,000 DEGREES CELSIUS
EARTHQUAKE WAVE STUDIES INDICATE A SOLID
CORE, AND THUS THE MAXIMUM TEMPERATURE
OF THE CORE WOULD BE 70000 C
SOURCES OF INTERNAL HEAT
1. RADIOACTIVITY
2. PRESSURE / COMPRESSION
3. Meteor impacts
Earth’s Magnetic Field
Earth’s Magnetic Field is tilted 11 degrees from
the north pole!