1. Causes of Seasons Earth’s Tilt Parallelism of Earth’s Axis
Path of Orbit
Earth’s Tilt – The Earth’s tilt affects the amount of direct & indirect sunlight a particular area of Earth receives. (This causes different temp & pressure changes)
Parallelism – The axis is parallel to itself. The north pole always points towards the same point in space – the star Polaris (also known as the north star)
Parallelism accounts for the intensity and duration of solar radiation an area of Earth receives.
Path of Orbit – The elliptical path is almost a perfect circle, but not quite. This path changes the distance between Earth and the Sun and though is not the main factor in causing seasonality, it can influence the severity of seasons.

2. Earth’s Tilt & Shape (23.45O) tilted sphere
Affects direct/indirect sunlight depending on latitude
What are the results of more or less direct sunlight on climate?
Earth’s Tilt – The Earth’s tilt affects the amount of direct & indirect sunlight a particular area of Earth receives. (This causes unequal heating which causes different temp & pressure changes which cause varying weather/climate conditions & severity based on latitude, proximity to water, proximity to mountain ranges, elevation and the influence of ocean currents.

3. Parallelism of Earth’s Axis
Parallelism – The axis is parallel to itself as the Earth orbits the sun. The axis is reasonably fixed at 23.5 degrees (adjusting for a 26,000-40,000 year wobble). The north pole always points towards the same point in space – the star Polaris (also known as the north star)
Parallelism accounts for the intensity and duration of solar radiation an area of Earth receives & therefore the intensity and duration of seasons. It also makes consistent seasonality possible. We always have the same seasons in the same order. With some exceptions, our climate on Earth has been quite stable for a very long time.

4. Polaris Graphic on left shows Earth’s north pole pointing to Polaris.
Graphic on right shows Polaris’ location in the “little dipper” in relation to the “big dipper.” The big dipper is in the Constellation Ursa Major and the little dipper in Ursa Minor.

5. Path of Orbit Elliptical path
Predict: In which direction (clockwise or counter-clockwise) does Earth orbit the Sun?
Changing distance from the Sun
Predict: How would our distance from the Sun affect seasons?
Path of Orbit – The elliptical path is almost a perfect circle, but not quite. This path changes the distance between Earth and the Sun and though is not the main factor in causing seasonality, it can influence the severity and duration of seasons.
The path of orbit is consistent. We always circle the Sun in a counter-clockwise rotation. This means the order of our seasons is also consistent.
The distance from the sun has no real affect on the seasons other than to change the # of days by a couple.

6. Path of Orbit

7. REVIEW Pair - Share: Establish groups of 3
Each student will share & EXPLAIN what they recorded for notes for 1 factor which causes seasons.
Group will update any omissions, discuss, & offer contributions.

8. Imaginary Lines
The Arctic & Antarctic Circles receive the least amount of sunlight.
The Equator receives the most direct sunlight.
The areas between ON & S latitudes (Arctic & Antarctic Circles) are known as Polar Zones. (Mostly cold. No significant seasonal changes.)
The areas between 23.5ON & S latitude (between the Tropics of Cancer & Capricorn) is known as the Torrid Zone. (Mostly hot & dry, no significant seasonal changes.)
The area between ON latitude (between the Tropic of Cancer & Arctic Circle is known as the Northern Temperate Zone. (Seasonal changes occur here.)
The area between OS latitude (between the Tropic of Capricorn & Antarctic Circle is known as the Southern Temperate Zone. (Seasonal changes occur here.)

9. Equinoxes & Solstices
Near June 21st, the summer solstice, the Earth is tilted such that the Sun is positioned directly over the Tropic of Cancer at 23.5 degrees north latitude. This situates the northern hemisphere in a more direct path of the Sun's energy. What this means is less sunlight gets scattered before reaching the ground because it has less distance to travel through the atmosphere. In addition, the high sun angle produces long days. (Higher sun angle is closer to 90o angle like it usually is at the Equator. Because the sun is shining more directly and for a longer period of time each day in this area of the world, it warms the atmosphere and oceans more and we experience our warmest season. Summer.
The opposite is true in the southern hemisphere, where the low sun angle produces short days. Furthermore, a large amount of the Sun's energy is scattered before reaching the ground because the energy has to travel through more of the atmosphere. Therefore near June 21st, the southern hemisphere is having its winter solstice because it "leans" away from the Sun.
Advancing 90 days, the Earth is at the autumnal equinox on or about September 21st. On the way, days are getting shorter. As the Earth revolves around the Sun, it gets positioned such that the Sun is directly over the equator. Basically, the Sun's energy is in balance between the northern and southern hemispheres and day lengths are equal (12 hours of day/night). The same holds true on the spring equinox near March 21st, as the Sun is once again directly over the equator.
Lastly, on the winter solstice near December 21st, the Sun is positioned directly over the Tropic of Capricorn at 23.5 degrees south latitude. The southern hemisphere is therefore receiving the direct sunlight, with little scattering of the sun's rays and a high sun angle producing long days. The northern hemisphere is tipped away from the Sun, producing short days (shortest day of the year is on 12/21) and a low sun angle.

10. REVIEW
During which events is the Sun directly over the Equator? Describe both how these events affects the amount of sunlight each hemisphere of the Earth receives and how the length of days in the northern and southern hemispheres compare with each other.
What season is it in the Southern Hemisphere if it is Summer in the Northern Hemisphere?
Equator – Spring & Fall Equinoxes (3/21 & 9/21). Both the northern & southern hemispheres of earth are receiving equal amounts of sunlight and the length of days is approximately 12hrs of light & 12hrs of night. This signals the coming of a change in the length of days. Shorter as you approach winter and longer as you approach summer. The tilt of the Earth moves where the direct sun shines. It’s either on the Tropic of Cancer in the Northern hemisphere, directly over the equator, or on the Tropic of Capricorn in the Southern hemisphere.
It is winter in the Southern hemisphere if it is summer in the Northern hemisphere because the southern hemisphere would be tilted away from the sun. This is due to the tilt of the Earth. This means that the direct sunlight falls more on the Tropic of Cancer in the Northern Hemisphere, which also has a high sun angle creating longer days. Longer days (sunrise-sunset) means the sun is available longer to heat the surface/water which happens in summer.

11. Exit Ticket What are the 3 factors that cause seasons?
Explain why days (sunlight hours) are longer in the summer compared to winter in the Northern Hemisphere?
3 factors – Earth’s titlt; parallelism of earth’s axis; path of orbit
Days are longer in the summer in the northern hemisphere because the Earth is tilted toward the Sun. This means the most direct sun is over the Tropic of Cancer and at a higher angle making days longer. A higher angle means the sun will rise earlier and set later making days (sunlight hours) longer.