The Seasons

Why do we have seasons? Earth’s distance from the sun varies throughout the year – doesn’t that cause the seasons? This was the most commonly given answer during a poll taken at a recent Harvard graduation Tilt! Because of the tilt of Earth’s axis, the amount of Insolation (incoming solar radiation) received by Northern and Southern Hemispheres varies seasonally A. Northern Hemisphere has summer when it tilts toward the sun, winter when it tilts away When it is summer in the northern hemisphere, it is winter in the southern hemisphere, and the other way around.

Insolation

What Causes the Seasons? The angle of the Sun matters: when the Sun is at a low angle, it does not heat as efficiently as it does when it is high angle.

For this reason, it’s warmer near the equator than at the poles. Seasons on Earth Angle of incidence… equator vs. poles North Pole Equator Earth South Pole Thus, Insolation is more intense near the equator compared to the poles. For this reason, it’s warmer near the equator than at the poles.

Earth North Pole South Pole Earth’s Seasons Tilt of the Earth’s axis towards or away from the sun creates the seasons When the north pole tilts toward the sun, it gets more radiation – more warmth during the summer SUMMER (Northern Hemisphere) North Pole Earth When the north pole tilts toward the sun, the south pole tilts away So when it’s summer in the north, it’s winter in the south South Pole WINTER (Southern Hemisphere)

Earth North Pole Equator South Pole Earth’s Seasons Tilt of the Earth’s axis towards or away from the sun creates the seasons WINTER (Northern Hemisphere) When the north pole tilts away from the sun, it gets less Insolation – So it’s colder during the winter North Pole Equator Earth South Pole When the north pole tilts away from the sun, the south pole tilts toward it… When it’s winter in the north, it’s summer in the south SUMMER (Southern Hemisphere)

What Causes the Seasons?

Because of the tilt of the Earth’s axis, the altitude of the Sun changes during the year: It gets higher above the horizon during the summer than it does during the winter. Summer: The combination of a long daytime and a Sun that is relatively high above the horizon leads to much more heating in the day, plus a shorter period of cooling at night. Overall, it is warmer

SEPTEMBER AND MARCH 22 Equinox

JUNE 21

DECEMBER 21