Reasons for the Seasons Chapter 17.1

Nearly 150 million kilometers separate the sun and Earth, yet solar radiation drives Earth's weather. At it’s Surface, the earth maintains an average temp of 59F With a wide range of temperature readings -121F during the Antarctica night 122F in deserts Figure 1.1

Does the distance from the Sun make the Seasons? NO The Earth is actually farther away from the Sun when we have our Summer.

Perihelion- Earth is closer to the Sun January 3rd

Aphelion- Earth is farthest from the Sun July 6th

Reason for the Seasons 1. The Earth’s tilt causes the seasons It is tilted at 23.5 degrees

The angle of the sun’s radiation (Insolation) hitting the Earth impacts the climate or temperature.

If the tilt were the only factor, then every location on Earth would have one season and it would never change.

2. Earth’s Revolution Causes the Suns rays to strike at different locations as the Earth orbits the Sun.

When northern hemisphere is facing the sun: •Summer Solstice (June 21st or 22nd )

SUMMER SOLSTICE Most direct rays over Northern Hemisphere •Striking at Tropic of Cancer 23.5° N. Light = 15 hours (about 14.27 (NC) Dark = 9 hours

Antarctica is completely dark for 24 hours and the Arctic is completely light for 24 hours!!!

Fall Equinox (September 22 or 23)

Direct rays over Equator: EQUAL amounts of daylight and darkness everywhere. Direct rays over Equator: Light = 12 hours Dark = 12 hours

Winter Solstice - December 21-22 SHORTEST DAY !!! Most direct rays over Southern hemisphere •Striking at Tropic of Capricorn 23.5°S Light = 9 hours Dark = 15 hours

Spring Equinox (March 21 or 22)

Direct rays over Equator: EQUAL amounts of daylight and darkness everywhere. Direct rays over Equator: Light = 12 hours Dark = 12 hours

The Southern Hemisphere has opposite Seasons than us . . . WHY?

Now on to stars for a brief moment!

Star Characteristics The color of the star can be a clue to its temperature. The hotter the star the shorter the wavelength the star emits.

Parallax Basic way to measure a stars distance from the Earth. Slight shifting of the apparent position of a nearby star due to the rotation of the Earth.

The closer the star the more it “moves” in the sky!

Remember this is an apparent motion…. like the Coriolis Effect Remember this is an apparent motion….like the Coriolis Effect ►caused by the Earth’s Revolution …not Rotation.

Light - Year The unit used to measure stellar (star) distance. The distance that light travels in one year. 9.5 x 1012 kilometers a year. 180,000 miles per second.