Why do we have seasons? Are the Seasons caused by the Earth being closer to or farther

away from the sun?

NOCloser to the sun in January, and farther away in July.

Perihelion is the point along Earth’s orbit when Earth is closest to the Sun.

January

Aphelion is the point along Earth’s orbit when Earth is farthest from the Sun.

July

Distance A

Distance B

Distance B (the tilt) is so small that it really does not make us any closer to the sun.

Why do we have seasons?Seasons are caused by different amounts of sunlight reaching earth because of a combination of

1. The tilt of Earth and

2. It’s revolution around the sun

Sun’s Path Across Sky

Sun’s Path Across Sky

Flashlight Activity

Flashlight Activity

NO – The amount of energy leaving the flashlight is the same at all times.

Likewise, the average amount of energy leaving the Earth receives is the same.

The energy is more concentrated in “A” because the energy is in a smaller area, therefor the temperature would be warmer. In B, the energy is spread out over a larger surface, decreasing the concentration and temperature.

In summer, the light hits us more direct, like in part “A”, the concentration is greater, we get a lot of heat therefore temperatures are warmer on average.

In winter, the light hits us indirectly, like in part “B”, the light is less concentrated and spread out, we get a little bit of heat therefore temperatures are cooler on average.

To Student 1: 0 Earth’s orbit is only slightly elliptical; we are

about the same distance from the Sun throughout the year.

0 For the Northern Hemisphere, we are actually closest to the Sun in the winter!

0 Distance from the Sun can’t explain seasons.

To Student 2: 0 You are confusing day and night with the reasons for

the seasons.0 Earth turns on its axis (rotates) once every day (24

hours). 0 When we are turned toward the Sun, it is daytime

(not summer).0 When we are turned away from the Sun, it is

nighttime (not winter).

To Student 3: 0 First, the tilt of Earth’s axis points toward the

North Star, so the December 21 Earth diagram needs to be tilted the other way.

0 Second, you seem to have forgotten that Earth rotates once every 24 hours, not once every 365 days (one year). The revolution of Earth around the sun takes 365.25 days.

TILT The tilt of earth effects the angle at which the sun’s rays

strikes the surface.

When rays strike at high direct angles, they are more intense, concentrated, and warm.

When rays strike at low indirect angles, they are spread out, less concentrated, and cool.

TILT The tilt causes different location to get different amounts of solar

radiation…just like our flashlights. Areas where the rays strike at high, direct angles get more intense

radiation and are warmer.

Areas where the rays strike at low, indirect angles get less intense light and are cooler.

TILT• If the tilt where the only factor, then every location on earth

would have one season and never change.

• One location would always receive the most direct rays and would always be hot. (On this graphic the Southern Hemisphere).

• Another location would always receive less intense rays and would always be cool.

Revolution• In addition to tilt, earth’s revolution is also a factor that

causes seasons.

• Earth’s revolution causes the suns most direct rays to strike at different locations as earth orbits the sun.

• When Northern hemisphere is facing the sun:• Most direct rays over Northern

Hemisphere.• Striking at Tropic of Cancer• Summer Solstice (June 21 or 22)

• When Northern hemisphere is facing away from the sun:• Most direct rays over Southern

Hemisphere.• Striking at Tropic of Capricorn• Winter Solstice (Dec.21 or 22)

• Neither Northern or Southern Hemisphere faces sun.• Direct rays over equator.• Autumnal Equinox (Sept.21 or 22)

• Neither Northern or Southern Hemisphere faces sun.• Direct rays over equator.• Vernal Equinox (March 20 or 21)

Seasons

Seasons

Seasons

Seasons

Length of Daylight• You probably noticed with seasons comes longer and

shorter days. Now you can understand why this is so…

• The main reason for longer and shorter daylight is earth’s tilt

Length of Daylight – Summer Solstice • When the Northern Hemisphere is tilted toward the sun =

Summer Solstice.

• More Sunlight covering the northern hemisphere than darkness.

• LONGER DAYLIGHT!

• June 21 or 22 – Longest Day of the Year

• Light = MORE (15 hours)

• Dark = LESS (9 hours)

Length of Daylight – Winter Solstice• When the Northern Hemisphere is tilted away from the sun =

Winter Solstice.

• More darkness covering the northern hemisphere than sunlight.

• SHORTER DAYLIGHT!• December 21 or 22 –

Shortest Day of the Year• Light = LESS (9 hours)• Dark = MORE (15 hours)

Length of Daylight - Equinox

• When the Northern Hemisphere is not tilted away from or toward the sun = Equinox (Vernal and Autumnal).

• Equal amounts of daylight and darkness everywhere.

• EQUAL DAYLIGHT!

• September 22 or 23 / March 22 or 23

• Light = 12 hours

• Dark = 12 hours

The Sun’s Path• From our perspective here on earth, the sun

“appears” to take a path across the sky as seen on the graphic.

The Sun’s Path• Notice that from March to June, the sun angle travels

high in the sky = warm, summer weather.

• It takes its longest path across the sky at this time, and thus, we have the longest amount of daylight (15 hours).

The Sun’s Path• From June to September, the sun angle gets lower in

the sky again. The lower angle means cooler weather and the start of fall.

• Notice how the path is shorter, and thus, the daylight hours start to get shorter.

The Sun’s Path• From September to December, the sun angle reaches its lowest

point. This means very little solar radiation and cold, winter weather.

• Notice that how the sun’s path is the shortest at this time, and thus the amount of daylight is also the shortest at only 9 hours.

The Sun’s Path• From December to March, the sun angle begins to rise

again, the days start to get warmer, and spring arrives.

• Spring is marked not only by warmer weather from the higher sun angle, but also longer days.

Click Here to View Website for Images

Why are There Seasons?

Season’s Concept Map

Northern, Southern, or Neither

T. Of Cancer, Equator, T. of Capricorn

Highest, Middle (Celestial Equator), or Lowest

0 hrs., 12 hrs., or 24 hrs.

0 hrs., 12 hrs., or 24 hrs.

0 hrs., 12 hrs., or 24 hrs.

Place Date

Draw a profile picture of Earth/Sun- Label N/E/S/W- Place Important Lines of

Latitude- Shade the night side of Earth- Place an “X” where the most

direct sunlight would be.- Indicate the hrs. of daylight at

important lines of latitude

Draw the sun in it’s track along the landscape.