Lecture 4

Earth/sun relationships

What percent of Earth’s energy is from the sun?

over 99%

The intensity of sunlight striking the Earth varies..

spatially with latitude and varies temporally with the seasons (day length) and btwn night and day.

Variations in sunlight intensity causes…

 __**unequal heating of the Earth’s surface, which transports energy across the globe**__**.**

Earth’s Movemenrts are..

Rotation on its axis and revolution around the Sun

Rotation

 **the spinning of the Earth on its axis**

Does the same side of the Earth always face the sun?

No, so the solar intensity varies

Which direction does the Earth turn?

counterclockwise when viewed above the North Pole.

Circle of illumination

forms between area of light (day) and dark (night)

Revolution

 **movement of the Earth in its orbit around the Sun (orbit is elliptical)**

Perihelion

**when the Earth and Sun and closest to each other. Occurs on January 4th, little higher solar intensity.**

**Aphelion**

**when the Earth and Sun are the furthest apart. Occurs on July 4th. little lower solar intensity**

Earth has seasons because of these 5 things

1. revolution 2. rotation 3. Tilt of Earth’s on Axis 4. Axial parallelism 5. sphericity

Earth has seasons due to

**Earth’s orientation to the Sun thus, the varying angle the Sun’s rays strike the Earth’s surface**

Tilt (inclination) of Earth’s axis is

**23.5º**

**axial parallelism**

orientation of the North Pole of the Earth toward a specific star

**sphericity**

the fact that the Earth is a sphere

Summer characteristics

longer days, higher solar altitude, more intense sunlight, more energy

Winter

shorter days, lower solar altitude, less intense sunlight and less energy

**Solar Altitude (SA)**

**the angle of the Sun above the horizon at any given latitude** **and varies with the seasons**

When is the March Equinox

**March 20-21 (start of Spring in NH and start of Fall in SH)**

When is the June Solstice?

**Jun 20-21 (start of summer in NH and start of Winter in SH)**

When is the September Equinox?

**Sept 22-23 (start of Fall in NH and start of Spring in SH)**

December Solstice

**Dec 21-22 (Start of Winter in NH and start of summer in SH)**

Climatological Winter months in NH

**Dec, Jan, Feb**

Climatological Spring months in NH

**Mar, Apr, May**

Climatological Summer months in NH

**Jun, Jul, Aug**

Climatological Fall months in NH

**Sep, Oct, Nov**