Agenda

Seasons Calendars Read unit 8 for Thursday

Why do we have seasons?

A. Earth’s distance from the Sun varies

B. The tilt of Earth’s axis

C. None of the above

Closest (perihelion)91,000,000 miles

Furthest (aphelion)95,000,000 miles

Jan 3 Jul 7

Variation of our distance to the Sun

Would you rather drive 717 miles?

Or 688 miles?

At 75 mph, this trip would be 23 minutes shorter

Closest (perihelion)91,000,000 miles

Furthest (aphelion)95,000,000 miles

Variation of our distance to the Sun

This variation in distance is really tiny!

When is Earth closest to the Sun (perihelion)?

A. June 21

B. January 3

C. July 4

D. August 15

E. March 26

Farthest from Sun (aphelion)

What does Earth’s rotation axis do as we orbit the Sun?

A. Always points outward

B. Always points inward

C. Points in a constant direction

What about our tilt?

We are always tilted at 23° with respect to our revolution

Northern hemisphereSummer Winter

Opposite seasons for Southern hemisphere

Giant marine life discovered in Antarctica’s Ross Sea

Associated PressMarch 21, 2008

late summer / early fall

What season is it right now in Antarctica?

A. Winter

B. Spring

C. Summer

D. Fall

Our tilt remains the same

First day of Winter(Northern Hemisphere!)

Winter solstice(December 22)

First day of Spring

Sunlight shines directly into the board

Spring (vernal) equinoxMarch 20

First day of Summer

Summer solstice(June 20)

First day of Fall

Sunlight shines directly out of the board

Autumn equinoxSept 22

Summers are warm because:

The Sun is higher in the sky Days are longer

Path of the Sun

wikipedia

Jupiter has a tilt of 3 degrees. Does it exhibit seasons?

A. Yes

B. No

C. Cannot conclude

Calendars

What use are calendars?

Why have them?

What calendar do we use here?

A. Julian

B. Gregorian

C. Hebrew

D. World Calendar

E. None of the above

Calendars of the world

Islamic – Lunar. New month starts on crescent moon

Chinese – Lunar and solar. New month starts on new moon

Mayan calendar

Calendars of the world

Hebrew – lunar and solar: a leap month is inserted ~ every 3 years

Julian: solar with 365.25 days in one year. Every fourth year is a leap year. (off by 11 minutes per year)

Gregorian calendar 365.2425 days

In 1582, skipped from Oct. 4 to Oct. 14 Leap day inserted every 4 years British empire did not switch until 1752

Sept. 2 was followed by Sept. 14 in 1752

Stonehenge!

Chaco canyon

In class drawing

In your notebook draw our orbit around the Sun

Label the following points

First day of each season Longest day and shortest day Your birthday Perihelion, aphelion

Another drawing…

Pretend you are facing South Label East and West Draw the path of the Sun through the sky

on: December 21 (winter solstice) June 21 (summer solstice) The equinoxes

E W

In your own words

Describe why the Earth has seasons

(include angle of the Sun, length of days)

Discuss your answers

With your group

If you took a picture of the Sun daily (same time and location)

What shape

would it trace out?

This is called the Analemma. What direction are we facing? Where is summer solstice in this picture? Where is winter solstice?