Agenda

1
Agenda

• Seasons
• Calendars
• Read unit 8 for Thursday

2
Why do we have seasons?

• Earths distance from the Sun varies
• The tilt of Earths axis
• None of the above

3
Variation of our distance to the Sun
Furthest (aphelion) 95,000,000 miles
Closest (perihelion) 91,000,000 miles
Jul 7
Jan 3
4
Would you rather drive 717 miles?
5
Or 688 miles?
At 75 mph, this trip would be 23 minutes shorter
6
Variation of our distance to the Sun
Furthest (aphelion) 95,000,000 miles
Closest (perihelion) 91,000,000 miles
This variation in distance is really tiny!
7
When is Earth closest to the Sun (perihelion)?

• June 21
• January 3
• July 4
• August 15
• March 26

Farthest from Sun (aphelion)
8
What does Earths rotation axis do as we orbit
the Sun?

• Always points outward
• Always points inward
• Points in a constant direction

9
What about our tilt?
We are always tilted at 23 with respect to our
revolution
10
Northern hemisphereSummer Winter
11
Opposite seasons for Southern hemisphere
12
Giant marine life discovered in Antarcticas Ross
Sea

• What season is it right now in Antarctica?
• Winter
• Spring
• Summer
• Fall

Associated Press March 21, 2008
late summer / early fall
13
Our tilt remains the same
14
First day of Winter(Northern Hemisphere!)
Winter solstice (December 22)
15
First day of Spring
Spring (vernal) equinox March 20
Sunlight shines directly into the board
16
First day of Summer
Summer solstice (June 20)
17
First day of Fall
Autumn equinox Sept 22
Sunlight shines directly out of the board
18
Summers are warm because

• The Sun is higher in the sky
• Days are longer

19
Path of the Sun
wikipedia
20
Jupiter has a tilt of 3 degrees. Does it exhibit
seasons?

• Yes
• No
• Cannot conclude

21
Calendars

• What use are calendars?
• Why have them?

22
What calendar do we use here?

• Julian
• Gregorian
• Hebrew
• World Calendar
• None of the above

23
Calendars of the world

• Islamic Lunar. New month starts on crescent
  moon
• Chinese Lunar and solar. New month starts on
  new moon

24
Mayan calendar
25
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)

26
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

27
Stonehenge!
28
Chaco canyon
29
In class drawing

• In your notebook draw our orbit around the Sun

30
Label the following points

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

31
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
32
In your own words

• Describe why the Earth has seasons
• (include angle of the Sun, length of days)

33
Discuss your answers

• With your group

34
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?