Earth’s Orbit Earth’s Orbit 4/29/144/29/14

IN: What causes the IN: What causes the different seasons on different seasons on the Earth?the Earth?

Remember…Remember…

The axis around which the Earth rotates is The axis around which the Earth rotates is tilted by 23.5 degrees with respect to the tilted by 23.5 degrees with respect to the ecliptic.ecliptic.

It is the tilt of the Earth that causes the It is the tilt of the Earth that causes the different seasons.different seasons.

The angle of the tilt never changes.The angle of the tilt never changes. It is the direction of the tilt that changes.It is the direction of the tilt that changes.

The sun’s rays The sun’s rays strike the strike the

Earth’s surface Earth’s surface at different at different

angles angles because the because the

surface is surface is curved.curved.

Indirect rays – light rays that do not hit the earth straight on.

Direct rays – light rays that do hit the earth straight on.

Sun's Rays Simulator

SeasonsSeasons

Earth-Sun RelationsEarth-Sun Relations

Tilt of the Earth’s AxisTilt of the Earth’s Axis

The axis around which the Earth rotates is The axis around which the Earth rotates is tilted by 23.5 degrees with respect to the tilted by 23.5 degrees with respect to the ecliptic.ecliptic.

It is the tilt of the Earth that It is the tilt of the Earth that causes the different seasons.causes the different seasons.

Summer SolsticeSummer Solstice

On June 21, the North Pole points directly On June 21, the North Pole points directly toward the sun.toward the sun.

On this day the North Pole has 24 hours of On this day the North Pole has 24 hours of sunlight.sunlight.

Summer SolsticeSummer Solstice

Midnight SunMidnight Sun

Winter SolsticeWinter Solstice

On December 21, the North Pole points On December 21, the North Pole points away from the sun.away from the sun.

On this day, the North Pole has 24 hours On this day, the North Pole has 24 hours of darkness.of darkness.

Winter SolsticeWinter Solstice

EquinoxesEquinoxes

On March 21 and September 21, neither On March 21 and September 21, neither hemisphere leans towards the sun.hemisphere leans towards the sun.

On these days, every place on earth has On these days, every place on earth has 12 hours of daylight and 12 hours of 12 hours of daylight and 12 hours of darkness.darkness.

EquinoxesEquinoxes

The angle of the tilt never changes. It is the direction of the tilt that changes.

Seasons MisconceptionSeasons MisconceptionMany people carry the misconception that the Many people carry the misconception that the

seasons are due to the distance of the Earth seasons are due to the distance of the Earth from the Sun. However, consider the following from the Sun. However, consider the following facts:facts:The Earth’s orbit around the Sun is nearly a perfect The Earth’s orbit around the Sun is nearly a perfect

circle. The Earth is slightly closer to the Sun in circle. The Earth is slightly closer to the Sun in January and farther from the Sun in July.January and farther from the Sun in July.

Seasons MisconceptionSeasons Misconception

While it is winter in the Northern While it is winter in the Northern hemisphere it is summer in the Southern hemisphere it is summer in the Southern hemisphere. If the seasons were due to hemisphere. If the seasons were due to our distance from the Sun both our distance from the Sun both hemispheres would have the same hemispheres would have the same seasons at the same time.seasons at the same time.

* Gravitation 3.8 Home Page — Normal * Gravitation 3.8 Home Page — Normal DisplayDisplay

OUT: Why do you think it is important to study the Earth’s orbit around the sun?