Sun’s Path

Part I. Earth’s Rotation Review

A. Proof1. Foucault Pendulum Experiment

a. Pendulum continues to swing in the same plane w/o changing direction

b. Change in direction is caused by the Earth turning beneath it

I. Earth’s Rotation Review

B. Direction of Rotation1. West to East

a. Sun rises generally in the east

C. Speed of Rotation1. 360 degrees / 24 hours = 15 deg/hr

2. Sun appears to move 15 deg/hr

Part 2. Celestial Objects

A. Objects in space that show daily movement as a result of Earth’s rotation

1. Sun = 15 deg/hr

2. Moon = 15 deg/hr

3. StarsA. Star trails

Part 3. Measuring AltitudeA. Maximum

altitude of sun is at solar noon.

Part 4. Measuring Azimuth

http://astro.unl.edu/naap/motion3/animations/sunmotions.html

Part 5. Key Dates

A. Equinox (Sept 21, March 21)1. Equal day, equal night

2. 12 hrs daylight EVERYWHERE on Earth

3. Sun rises in EAST and sets in WEST

4. Sun’s direct rays are hitting the equator (sun is directly overhead)

5. Vernal Equinox – Spring, 3/21

6. Autumnal Equinox – Fall, 9/21

5. Key Dates

B. Winter Solstice (Dec 21)1. Shortest period of daylight in Northern

Hemisphere, sun lowest in altitude2. Rises and sets farther south than any

other day3. Sun’s direct rays are at 23.5º South,

directly overhead at Tropic of Capricorn

4. 1st day of winter5. 24 hours of darkness North of Arctic Circle

5. Key Dates

C. Summer Solstice (June 21)1. Longest period of daylight in Northern

Hemisphere, sun highest in altitude2. Rises and sets farther north than any other

day3. Sun’s direct rays are at 23.5º North,

directly overhead at Tropic of Cancer

4. 1st day of summer5. 24 hours of daylight North of Arctic Circle

Part 6. Pattern of ChangeSept 21 – Dec 21 (Fall) Dec 21 – Mar 21 (Winter)

Sun’s Altitude

Length of Day

Sunrise / Sunset

Direct Ray’s of Sun

Lower

Shorter

Moving south (SE / SW)

Moving to Tropic of Capricorn (23.5º S)

Higher

Longer

Moving back to East and West

Moving to Equator (0º)

Part 6. Pattern of ChangeMar 21 – June 21(Spring) June21–Sept21 (Summer)

Sun’s Altitude

Length of Day

Sunrise / Sunset

Direct Ray’s of Sun

Higher

Longer

Moving north (NE / NW)

Moving to Tropic of Cancer (23.5º N)

Lower

Shorter

Moving back to East and West

Moving to Equator (0º)

Part 7. Seasons

WINTERSUMMER

FALL

SPRING

VII. Seasons

A. Caused by the Sun’s rays striking different areas of Earth’s surface

B. Reasons for the Seasons1. Earth REVOLVES around the Sun

2. Earth’s axis is tilted 23.5º

3. Parallelism of the axis (axis stays parallel while it travels around the sun)

http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.html

VII. Seasons

C. Season do NOT depend on the distance

from the sun – orbit is an ellipse!1. Closest to sun (Perihelion)

a. On January 4th

b. 91.5 million miles

2. Farthest from Sun (Aphelion)a. On July 3rd

b. 94.5 million miles