1. Aim: What causes Seasons?
Notepack 28
Aim: What causes Seasons?
Do Now: What is the difference between revolution and rotation?

2. Earth’s rotation
The Earth rotates on its axis (imaginary vertical line around which Earth spins) every 23 hours & 56 minutes. (counter clockwise)
One day on Earth refers to the length in time that it takes for one rotation of the Earth.
Daytime on Earth is when one side of the Earth faces the sun.
Nighttime on Earth is when the side of Earth we are on faces away from the sun.

3. A Day on other Planets
On Jupiter, a day takes only 9 hours and 50 minutes.
On Venus, a day last 243 Earth days.

4. Earth’s revolution
It takes the Earth 365 days (or rotations) to travel or revolve around the Sun once.
One complete revolution is called a year.

5. A Year on other Planets On Mercury, one revolution takes only 88 days.
On Neptune a revolution takes almost 165 Earth years.

6. Earth’s orbit
The Earth’s orbit around the Sun in not a perfect circle.
The Earth’s orbit has an elliptical shape (oval).
Because the Sun is closer to one side of the ellipse, the Earth’s distant from the Sun changes as it goes around the Sun.

7. Perihelion- When Earth is closest to the sun
Aphelion – When Earth is furthest from the sun

8. Why do we have seasons?
Seasons are not caused by how close the Earth is to the sun.
In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4.

9. Why do we have seasons? (cont)
Seasons are the result of the tilt of the Earth's axis.
Earth’s axis is tilted 23.5°.
This tilting is why we have SEASONS like fall, winter, spring, and summer.
The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun.
The more daylight hours , the more time the ground has to be warmed up by the Sun.

10. ANGLE OF INSOLATION
The angle at which the sunlight hits the Earth is called the Angle of insolation.
The higher the angle the more heat that location receives.
The more heat the ground gets, the warmer the air will be.

12. Why do we have Seasons? (cont)
Because the Earth’s tilt always points towards Polaris and the Earth revolves around the Sun, The Northern and Southern Hemispheres receive different amount of light throughout the year.
When the North pole points towards the Sun, it is Summer in the Northern Hemisphere and Winter in the Southern Hemisphere..
When the North pole points away from the Sun, it is Summer in the Southern Hemisphere and Winter in the Northern Hemisphere.

13. N S N S

14. Why do we have seasons? (cont)
Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter

15. Why do we have seasons? (cont)
Also the days are much longer than the nights during the summer.
During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short.

16. Seasons…in a nut shell

17. The Movement of the Sun across the sky during the change of seasons.
Because the amount of sunlight areas receive between Summer and Winter changes, the Sun appears to travel north and south throughout the year.
This is an apparent movement – The Sun isn’t moving but it is the revolution of the Earth and its tilt that actually cause this affect.

18. The Movement of the Sun across the sky during the change of seasons.
In the Northern Hemisphere, the Sun travels furthest north during the Summer months.(June)
In the Northern Hemisphere, the Sun travels furthest South during the Winter months. (December)
In the Southern Hemisphere it is opposite

20. Solstice
Solstices occur twice a year, when the tilt of the Earth's axis is oriented either directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.
The days of Solstice has either
The longest day of the year – about 16 hours
Or the shortest day of the year – about 8 hours

21. Winter Solstice
Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.

22. Winter Solstice
During the winter solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.
Sunlight strikes the Earth most directly at the Tropic of Capricorn. 23 ½ degrees South Latitude.

23. Summer Solstice
The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer.

24. Summer Solstice
During the summer solstice, the North Pole has a 24-hour Day and the South Pole has a 24-hour night.
Sunlight strikes the Earth most directly at the Tropic of Cancer. 23 ½ degrees North Latitude.

25. Shadows during the Solstice
During the Winter Solstice, shadows are at their longest.
During the Summer Solstice, shadows are at their shortest.

27. Equinoxes
An Equinox is when the northern and southern hemispheres experience 12 hours of day and 12 hours of night.
Equinox literally means "equal night".
Sunlight strikes the earth most directly at the equator.
This occurs twice a year:
The vernal (spring) equinox occurs March 21.
The autumnal (fall) equinox occurs September 21.

28. Equinox