Office HoursTue: 12:30 PM to 2:30 PMWed: 9:00 AM to 10:30 AM & 12:00 PM to 2:00 PMThr: 9:00 AM to 10:30 AM

Course Syllabus can be found at:

http://www.wx4sno.com/portfolio/BSU/Fall_2011/

This lecture will be posted AFTER class at:

http://www.wx4sno.com/portfolio/BSU/Fall_2011/Lectures/

Lesson 10Earth-Sun Relationships

Hess, McKnight’s Physical Geography, 10 ed.

15-21 pp.

Terms to KnowRotation: Earth completes one

rotation every 24 hours giving us day and night.

Terms, cont.Revolution: Earth completes one

revolution around the sun every 365 ¼ days.

Terms, cont.Revolution is not a perfect circle, more

of an elliptic. When revolution brings earth closest to sun:

perihelion When revolution takes earth furthest from sun:

aphelion

Point 1: Earth at aphelion

Point 2: Earth at perihelion

Point 3: Sun

Perihelion and Aphelion, cont.

Terms, cont.Ecliptic plane: This is the level, or

plane, of Earth’s orbit around the sun…Earth’s orbital path.◦ Astronomically, this is the primary plane

referred to when discussing the revolution of other planets around the sun

Terms, cont.Inclination: Relative to the ecliptic

plane, Earth is tilted 23.5° from vertical at all times.

Terms, cont.Polarity: Because Earth is always

tilted 23.5°, it’s axis is always pointed in the same direction…towards the star Polaris.◦ Because of this regular tilt, when the Earth

revolves around the sun, the North pole is either tilted towards the sun (June) or tilted away from the sun (December)

◦ DO NOT confuse this with Earth’s magnetic field!

Earth’s EquinoxesEquinox: Earth is positioned so that

its is neither towards nor away from the sun…giving the entire planet equal amounts of day and night.◦ Occurs twice each year, around March 20

and September 22.

Earth’s Solstices Solstice: Earth is positioned where its tilt is either

towards or away from the sun.◦ Occurs twice a year, just like the Equinoxes, around June

21 and December 21.

◦ The direct rays from the sun hit the earth at 23.5°N on June 21, while the tangent rays hit the earth around 66.5°N and 66.5°S.

Sun’s Rays during Equinoxes

Sun’s Rays during Summer Solstice

Sun’s Rays during Winter Solstice

Video on Seasonshttp://

www.youtube.com/watch?v=taHTA7S_JGk

Powers of ten:◦http://youtu.be/vRjGarICal4◦http://youtu.be/0fKBhvDjuy0