The ReasonS for the Seasons Lesson 4

In which direction does Earth’s axis point as it revolves around the Sun?

Approximate Distance to Polaris: 434 Light Years 2,386 Trillion Miles

In which direction does Earth revolve around the Sun?

A resource guide for finding the material for the back page.

This diagram is greatly over exaggerated Perihelion (Closest) =147,098,291 km Aphelion (Furthest) =152,098,233 km

The relative to scale size of the Earth’s elliptical (oval shaped) orbit: (Would you have called it a circle?)

Perihelion (closest to the Sun) January 4th Aphelion (farthest from the Sun) July 4th January 4th July 4th So why do we have such a strong misconception about the cause of the seasons?

The Angle of the Sun’s Solar Radiation

Less Direct/Intense More Direct/Intense

Northern Hemisphere is pointed more toward the Sun. pointed more away from the Sun.

This data is pretty close for our location: (Seattle is close to 47°N latitude) Summer – 16 hrs of daylight, angle of sun 63°, average high temp 71°F Fall – 12 hrs day, angle 40°, high temp 67°F Winter – 8 hrs day, angle 16°, high temp 47°F Spring – 12 hrs day, angle 40°, high temp 58°F

Big Ideas: Yes it is true that the seasons are caused by the tilt of the earth, but . . . The tilt of the earth determines how much solar radiation (sun’s energy) we receive. And. . . Where we are in our orbit determines whether we are tilted toward or away from the Sun. When the Northern Hemisphere is tilted toward the sun (summer solstice/June 21st) we not only receive more solar radiation (longest day of the year), but we are being hit by a more direct angle increasing the intensity of the solar radiation.

Big Ideas (Continued) During our winter solstice (Dec. 21st) we receive less solar energy (shortest day of the year) and the solar energy is hitting us at a less direct angle so the energy is spread out more and as a result weaker. Solstice - longest/shortest day of the year. Equinox - equal day and night world wide. (Continued)

Big Ideas (Continued) March 21st Spring (Vernal) Equinox (NH) June 21st Summer Solstice (NH) Sept. 21st Fall (Autumnal) Equinox (NH) Dec. 21st Winter Solstice (NH) NH = Northern Hemisphere. The seasons are reversed for the Southern Hemisphere.