Why are There Seasons?

Cause of Seasons Parallelism – Earth is always pointed in the same direction as it orbits the sun. Earth is orbiting the sun on a 23.5 degrees tilted axis Because the Earth is orbiting on a tilted axis the angle of sunlight changes and as the angle of sunlight increases the warmer seasons are approaching. Cause of Seasons The Earth is orbiting the sun on a 23.5 degree tilt always leaning toward the same direction http://www.eram.k12.ny.us/education/components/docmgr/default.php?sectiondetailid=17500&fileitem=4943&catfilter=452

Seasons are NOT caused by distance to the sun Since Earth’s orbit is Elliptical and is not a perfect circular orbit our distance from the sun Changes. BUT THIS IS NOT THE REASON FOR SEASONS Elliptical orbit – slightly flattened circle Perihelion – point when the earth is closest to the sun JANUARY 3RD (WINTER) Aphelion – point when the Earth is furthest from the sun) JULY 4th (SUMMER) I REPEAT: Seasons are NOT caused by distance to the sun

Summer Solstice Solstice – sun Stop ** on the summer solstice the sun stops moving higher in the sky. June 21st – Suns vertical rays (90 degree) are over the Tropic of Cancer 23.5 north North Pole pointed at the sun Sun Rises North due east (off the tropic of cancer and. Sun sets north due West (on the Tropic of Cancer) Northern Observers – Sun is highest in our Sky (highest angles of insolation) Longest day of the year NY observers – 15 hrs of sunlight North pole receives 24 hours of sunlight

Summer Solstice

Winter Solstice December 21st – suns vertical rays are over the Tropic of Capricorn (23.5 south) Winter solstice – Sun stops dropping in the sky Sun rises south (23.5 S) and Sets 23.5 South due West. North pole is pointed away from the sun Lowest angle of insolation Shortest Day – 9 hrs for a NY observer

Winter Solstice

Spring/Vernal Equinox March 21 – suns Direct rays are over the EQUator. Sun Rises and sets on the EQUator There are equal hours of sunlight to night for the entire earth.

Spring Equinox

Fall/autumnal Equinox September 21-23 Sun rises Due East and sets due West on the equator All locations on Earth receive 12 hours of sunlight and 12 hours darkness.

Suns Path Diagrams – Northern Observers

You Must memorize this!!

Suns path – Observer at North pole on June 21st Remember the North Pole is receiving 24 hrs of sunlight and the sun never sets. It’s still not warm b/c even though they are receiving 24 hrs of sunlight they are receiving low angles of insolation

Suns path – Spring and Fall Equinox – observer at the equator