Earth

Physical Characteristics of Earth

1. Spherical shape

-satellite photos

-curved shadow on moon during a lunar eclipse.

-approaching ships “rise” over the horizon

Physical Characteristics of Earth

2. Rotation-Earth spins on its axis (an imaginary vertical line) causing night and day.-24 hours to rotate once on its axis-rotates 365 times in a year

Foucault’s Pendulum shows the Earth’s rotation as it swings

https://www.youtube.com/watch?v=R3jr0DaV8N8

Physical Characteristics of Earth3. Magnetic Field

-Movement of liquid iron inside Earth and its rotation create a magnetic field.

-Helps protect Earth from harmful CME’s from the sun.

Physical Characteristics of Earth

4. Revolution

-Earth’s yearly orbit around the sun. (365 ¼ days)

-Path is elliptical in shape.

Farthest away

from sun in July

Closest to sun in January

What causes the seasons?

??

?

What do you know about the Seasons?

• Summer– NJ-warm, longer days,

June-August– Hawaii-80’s, 12 hours

of light– Alaska- up to 24 hours

of light– Australia-Dec-Feb

• Winter– NJ-cold, longer nights,

Dec-Feb– Hawaii- 70’s, 12 hrs of

light– Alaska-up to 24 hours

of darkness– Australia-June-Sept.

Distance from the sun does NOT cause our seasons.

• If it did, we would all feel winter in July and summer in January. Even Hawaii would have a cold winter!

Physical Characteristics of Earth

5. A Tilted Axis

23.5˚ tilt

-The Earth is always tilted the same direction during its yearly revolution around the sun.

• Sunlight strikes the hemisphere tilted towards the sun more directly than the hemisphere tilted away.

• Summer occurs in the hemisphere tilted towards the sun. (direct light)

Sun

Direct Light• Areas receiving direct light from the Sun

have a greater amount of sunlight, therefore higher temperatures.

What season is it?

Sun

Northern Hemisphere-Winter

Southern Hemisphere-Summer

So what causes the seasons?

• The Earth’s tilt causes the seasons!http://lhsgems.org/Presentations/SSS%203-8%20NSTA%202009%20final.ppt#362,35,Another Model for Distance

Solstice• The day when the sun reaches its greatest

distance north or south of the equator.• Northern Hemisphere- (opposite of S. Hemi)

– Summer solstice: June 21 or 22 (longest period of daylight of the year)

– Winter solstice: December 21 or 22 (shortest period of daylight of the year)

The sun’s path across the sky is higher in the summer and lower in

the winter

http://www.newscientist.com/blogs/shortsharpscience/2011/10/about-time-beer-can-freezes-ti-1.html

Equinox• When the sun is directly above the Earth’s

equator. Daylight hours are nearly equal all over Earth.– Neither the N. or S. Hemisphere is tilted

towards the sun.– Spring equinox-March 20 or 21– Fall equinox-September 22 or 23

Seasons demos

• https://www.youtube.com/watch?v=DD_8Jm5pTLk

• http://esminfo.prenhall.com/science/geoanimations/animations/01_EarthSun_E2.html

http://spiff.rit.edu/classes/phys301/lectures/gas_planets/Seasons_Nav.swf

Northern Hemisphere Solstice and Equinox positions

Seasons are opposite for the Southern Hemisphere

Review Quiz

Which diagram correctly shows Earth’s orbit around the sun?

Identify for the N. Hemisphere:

1. Summer solstice

2. Winter solstice

3. Fall equinox

4. Spring equinox

A

D

C

B

Summer

Spring

Winter

Fall

How do we know the Earth is a sphere?

-satellite photos

-curved shadow on moon during a lunar eclipse.

-approaching ships “rise” over the horizon

What is an axis?

• The imaginary vertical line around which the Earth spins.

What does “A” represent? What does “B” represent?

A

A-Revolution B-Rotation

B

How long does one complete rotation take on Earth?

• 24 hours

How long does one complete revolution of Earth take?

• 365 days (1 year)

Why is a magnetic field important?

• It protects Earth from CME’s from the Sun

How do we have a magnetic field?

• The motion of the liquid metal inside Earth and our daily rotation cause it.

What causes the seasons?

• TILT! TILT! TILT!

What season is it in the Southern Hemisphere?

• Summer-southern hemisphere is tilted towards the sun = direct light = summer!

Sun

What type of light makes hotter temperatures?

• Direct!

Where is the sun during the equinox?

• Directly over the equator.

What’s the difference between northern and southern

hemispheres’ seasons?• They are opposite!

Christmas (December) in Australia is warm!

Easter is celebrated in the fall (March or April)

• http://www.teach-nology.com/worksheets/science/earth/4/