Earth Systems

How do we know the Earth is round?

Entry Task

We all know the Earth is round (a sphere)…

How do you know it is round?

More importantly,

How did people more than 2000 years ago

(14 centuries before Columbus) figure out that Earth was round?

Two Models of Earth

Round vs Flat

How could you use these models to gather evidence of the Earth’s

shape?

Latitude like rungs of a ladder

Start at the Equator (0°)

Are described by their distance north or south of the equator

Example: the North Pole is 90° North of the equator

Longitude all are long

0° longitude runs through the English town “Greenwich”(Grenich)

The line half way around the world is 180° E/W runs through Fiji (the international date line)

How do observations of ships at sea provide evidence of Earth’s shape?

Make a model sailing ship

Sail your ship from one location to another on each modelGet your eyes as close to the

starting point as possible (to view as if you were on the ground)

Record your observations on “Shape of Earth”

Shrinking vs Sinking

In which model does the ship appear to shrink as it gets

farther from it’s starting port?

In which model does the ship appear to sink as it gets

farther from it’s starting port?

A little history…

Ships carried materials and goods

Merchants waited on shore for delivery

Would observe first the topsail, then mainsail, then hull appear from the sea

When boats left, same observers saw Hull, then main sail, then topsail disappearing into sea

Sailors always watched for land

Sailors in the crow’s nest always sighted land first

Sailors on deck would not see land for several more minutes

Homework:

Round Earth Flat Earth Simulation & Questions