Astronomy

Rotation and Revolution

They’re like “Night and Day”

What We Know

• We all know that the earth rotates– It spins like a top about its axis

• We also know that it revolves– It moves as a whole body around the sun

• This rotation and revolution cause– Night and day– Seasons

Day and Night

• The earth rotates about its axis• The portion of the earth that faces the sun

experiences day• The portion facing away experiences night

It’s All in a Day

• One spin equals– 1 day or– 24 hours or– 1 sunrise until the next sunrise

1 spin = 1 day = 24hrsAnimation

So, What Is a Year??

What’s Up with that Extra ¼ Day

• The calendar normally has 365 days• The extra ¼ day must be accounted for in

order to make sure we’re at the same point on the path (the X) each year

• So, an extra day is added to February every 4 years

• This special year has 366 days and is called a “Leap Year”

What’s Up with that Extra ¼ Day

If you were born on Feb. 29th, you would only have a birthday every 4 years!!

Happy birthday to you in 2004, since this is a Leap Year.

The Earth Is a Tilted Planet

• The earth rotates about its “axis of rotation”

• The axis of rotation is tilted 23.5° off of an imaginary plane that slices through its orbital path around the sun

• What is the effect of this tilt?

The Earth Is a Tilted Planet

In the summer, we in the northern hemisphere are tilted toward the sun

In the winter, we in the northern hemisphere are tilted away from the sun

The Earth Is a Tilted Planet

In the spring, we in the northern hemisphere are tilted neither toward nor away from the sun

In the autumn, we in the northern hemisphere are tilted neither toward nor away from the sun

Summer’s Hot

• In the summer, the tilt causes us to receive more direct sunlight

• This direct sunlight warms the earth more than indirect sunlight

Winter’s Not

• In the winter, the tilt causes us to receive less direct sunlight

• This lack of direct sunlight causes us to get cold

Let’s Compare

• Notice the difference in the spacing between the red lines that correspond to the gray band that shows where we live

What About Spring and Fall

• During the equinoxes (spring and fall) we are neither tilted toward nor away from the sun. (We’re tilted into the page)

Vocabulary Time!

• Summer solstice – June 21st

– The 1 day of the year when the north pole points the most toward the sun

– The longest day of the year for those in the northern hemisphere, and the shortest for those in the southern

Vocabulary Time!

• Winter solstice – December 21st – The 1 day of the year when the north pole

points the most away from the sun– The longest day of the year for those in the

southern hemisphere, and the shortest for those in the northern

Vocabulary Time!

• Spring and Fall Equinoxes (March 21st and September 21st)– The 2 days of the year when the north pole

points neither toward nor away from the sun– Every point on earth experiences 12 hours of

daylight and night

Things That Make You Go Hmm

• At the equator, every day is both 12 hours of daylight and 12 hours of night all year

• Any point above the “Arctic Circle” will have at least 1 day of complete sunlight, and 1 day of complete darkness each year

• Any point below the “Antarctic Circle” will also have at least 1 day of complete sunlight, and 1 day of complete darkness each year

• These days are the winter and summer solsticesAnimate

Have You Noticed It’s Getting Lighter Each Morning?

• As we get further from the winter solstice, the days are getting longer

Animate

Rotations and Revolutions

It’s Not Magic

It’s Science