1. The Reason for the Seasons
Life 4 Leaves
School's Out!
Brrrrrrrrrr!
Leaves go down!

2. #1 Here’s Mars… Where would you guess that it is COLDEST …you’re
on Mars?
…you’re
right. But
why? And
how did you
know?
If you guessed
here…
…and here…

3. #2 The key is that Planets are…
ROUND

4. #3 …and sunlight comes in from just one direction
½ of Jupiter lit by the
Sun
light

5. #4 It’s all about CONCENTRATION!
Venus, lit by the Sun
Look at a ray of sunlight
hitting the middle of the
planet.
The ray hits this part of
the planet directly, giving
it a lot of energy (HEAT!),
and focusing this energy
over a small area.

6. #5 But at the north & south pole?
That same picture of Venus
Here comes a ray from
the sun toward the south
pole of Venus…
the direct ray of light
notice how much bigger an area the ray
covers…this means it’s
LESS concentrated!

7. #6 So direct light heats planets up more than slanted light!
YUP!
Around the middle of the planet, the light is very focused
and hits directly, heating that area up greatly.
But at the top and bottom of the planet, the light comes
in at a slant, meaning it warms those areas much less.

8. #7 So that explains why…
The best planet ever!
Up here we have…

9. #8 …and…
Around here we have…
The best planet ever!

10. #9 …and…
Down here we have…
The best planet ever!
I’m hot

11. #10 This helps, but it doesn’t explain the seasons!
So far we only know why the hottest part of each planet
is around the middle…the sunlight hits that part most directly.
If that was all that happened, though, we WOULDN’T have
different seasons…just the same boring weather all year long.
In Texas, it’d be about 90 degrees every day of the year with
occasional rain. Not bad, but definitely BORING.

12. #11 This is the key, so repeat after me…
It’s…
the…
TILT

13. #12 The Earth doesn’t sit perfectly straight up and down
A “false” view of
Earth rotating on its
axis.
This just isn’t right!

14. #13 Our Axis is TILTED!
TILT
About 23.5 degrees

15. #14 A more accurate view…
Notice the…
TILT

16. #15 Remember from earlier…
…That the middle of the planet gets the most direct sunlight
(heat).
COLD
medium
HOT

17. #16 So one half of the Earth “tilts” toward the sun!
Yep!
Direct light = Summer!
Slanted down here = Winter!
Which hemisphere of Earth (Northern or Southern) is having
Summer & Winter in this diagram?

18. #17 What’s this mean for Texas?
When our Northern Hemisphere tilts toward the Sun, we
actually get nearly the most direct sunlight of anywhere on the
planet! No wonder we get over 100 degrees so often in July &
August!

19. #18 So…how do we get Winter here???
That happens when our (Northern) hemisphere tilts away from
the sun.
Summer
down
here!

20. #19 And the final piece to the puzzle?
So, the TILT is a big part of it, but something else must
cause us to tilt either away or toward the Sun at different
times during the year…
…and that last bit is something you’ve known for years!
The Earth revolves around the Sun!
Watch the animation…pay
attention to the direction
Earth’s axis points as it
orbits the Sun.

21. #20 So it’s a combination of the TILTed axis and our revolving!
Yeah!!!

22. #21 The Earth reaches 4 important points in its orbit
Summer Solstice
Late June
TX tilted toward Sun
Longest day, shortest night
Begins Summer

23. #22 Three months later… Autumnal Equinox Late September
TX tilt balanced
12 hrs day, 12 hrs night
Begins Autumn/Fall

24. #23 Three months later… Winter Solstice Late December
TX tilted away from Sun
Shortest day, longest night
Begins Winter

25. #24 Three months later… Vernal Equinox Late March TX tilt balanced
12 hrs day, 12 hrs night
Begins Spring

26. #25 And this cycle continues over and over…
…completing every 365 ¼ days, which we call
a “year.” By our best estimation, this process
has happened approximately…
4,500,000,000 TIMES
Yeah, we’re old.

27. #26 So, In Summary…
If somebody asked you, “Why do we have seasons on Earth?” you
could now answer with great confidence…
Fact 1: Round planets heat up wherever they get direct sunlight
and are cooler at the tops and bottoms.
Fact 2: The Earth’s axis is TILTED 23.5o.
Fact 3: As Earth revolves around the Sun, the tilt causes different
parts of it to receive more or less sunlight for a few months,
causing the weather and daylight to change.

28. #27 and…
THAT is the reason for the seasons!
The End!