Chapter 13 – Atmosphere and Climate Change Section 1a – Climate - Seasons

What causes Seasons? The Earth is tilted 23.5° on its axis. This tilt allows for different seasons and for different amounts of daylight and night time.

Seasons in Different Hemispheres The tilt of the Earth also allows for the Northern and Southern Hemispheres to have different seasons at the same time.

Earth Movement Earth rotates around its axis once per day, causing day & night. Earth revolves around the Sun on an elliptical orbit every year. This revolution and the Earth’s tilt cause seasons. The North Pole always points toward the North Star.

Summer in Northern Hemisphere Earth is positioned so that the Northern Hemisphere is tilted towards the Sun. Most of the direct rays from the Sun are hitting the Northern Hemisphere. This causes increased temperatures and longer days.

Fall/Spring In Northern Hemisphere Earth is positioned so that the north pole is neither pointed towards or away from the Sun. The Northern and Southern Hemispheres received equal amounts of direct rays from the Sun.

Winter in Northern Hemisphere Earth is positioned so that the North Pole is now pointed away from the Sun. Most of the direct rays from the Sun are hitting the Southern Hemisphere. This causes lower temperatures and shorter days.

Summer Solstice (June 20/21) Solstice when the Sun reaches its highest or lowest point in the sky at noon. Usually occurs on June 20/21. It is the longest day of the year in the Northern Hemisphere.

Autumnal Equinox (Sept 22/23) Equinox from Greek words meaning equal and night, an equinox is a day in which there is equal amounts of daylight and night time. Usually on September 22/23

Winter Solstice (Dec 21/22) Usually occurs on Dec 21/22. Shortest day of the year in the Northern Hemisphere.

Vernal Equinox (Mar 20) One of two days where there is equal amounts of daylight and night. Usually occurs on March 20.