Science Part 1 of Unit 2 Quiz

Oblate Spheroid

shape of the earth- an imperfect sphere. slightly oblong, almost a sphere but not quite.

Earth’s Equatorial Dimensions

Equatorial Diameter = 12,756 Km

Equatorial Circumference = 40,075 Km

Earth’s Polar Diameter

Polar Diameter = 12,714 Km

Polar Circumference = 40,008 Km

Horizon

Your line of sight parallel to earth’s surface.

Zenith

Point directly overhead.

Altitude

The angular height an object is in the sky.

Apex

Highest point of an Arc.

Sextant / Astrolabe

an instrument used to measure the altitude of an object above the horizon

Evidence Earth is Round- Spherical Earth

Ships disappear hull first, and mast last as it sails over the horizon.

Evidence Earth is Round- Star Positioning

The position of Stars (and Sun) in the sky appear to change as

our Latitude changes on Earth’s surface.

Changing Position of Stars, specifically Polaris

For every of 1° of latitude we move N/S, Polaris will become 1°alt higher/lower in the sky!

Finding Polaris in New York (Yorktown)

Evidence Earth is Round- Weights Change Around Globe

Maximum weight at poles. Minimum weight at equator.

Gravity Measurements

The further an object gets from the center of the Earth (Core), the less it weighs.

Evidence Earth is Round- Shadows 

The lunar eclipse casts a round shadow of the Earth on

the moon.

Evidence Earth is Round- Photographs

Satellite photographs of the Earth taken from space provide

the best piece of evidence!

Eratosthenes

The man who measured the world.

Where and When was Eratosthenes born?

• 276 B.C

• City of Cyrene ( now Libya) 

When did he die and how old was he?

• Died in Alexandria in 194 B.C.

• Died at 80-84 years

What term did Eratosthenes coin? 

Geography 

What was Eratosthenes title?

Head Librarian in library of Alexandria

At which cities did he make the discovery that at 12 noon there was a shadow from the sun in one, but the sun cast no shadow in the other because it was directly overhead? 

Alexandria (shadow) and Syene (no shadow) 

What did he conclude that the angle between the top of the obelisk at noon was?

7.2 degrees of arc

Euclid

father of geometry

How many degrees of latitude separate the cities?

7.2 degrees

Circumference Math

How did he find the distance between the 2 cities, and what was it? 

• He hired a peasant to walk the distance (twice for accuracy)

• 800 kilometers (about 500 miles)

How many meters does 1 stade/ion equal?

About 160 m

Final Formula for Finding Circumference

__θ__ = __d__

360° _____C

Final Formula- what math strategy was used? 

Cross Multiplication

Eratosthenes Final Circumference of the Earth

C = 40,000 km

What was Eratosthenes percent error, knowing the Earth is really 40,041.5km?

0.1% error

This is very impressive and low for 2260 years ago. 

Centrifugal Effect

what causes the Earth to be an oblate spheroid. Force resulting from Earth’s rotation. Means center fleeting (the result of rotation) 

Merak and Dubhe

stars in the big dipper that point to Polaris

Cassiopeia

Is opposite the Big Dipper and useful in finding Polaris.