REVIEW The Electromagnetic Spectrum Figure 2.5 Figure 2.6

Solar and Terrestrial Energy Figure 2.7 II. Solar Energy: From Earth to Sun Sun emits: 8% UV, x-ray, gamma radiation 47% visible radiation 45% infrared wavelengths

Distribution of Insolation Tropics receive more concentrated insolation due to the Earth’s curvature Tropics receive 2.5X more than poles Subsolar point REVIEW

Lecture 3: The Seasons Seasonality Reasons for Seasons Annual March of the Seasons The Tides

Seasonality Seasonal changes Sun’s altitude – angle above horizon Declination – location of the subsolar point Daylength

The Suns Position

Reasons for Seasons Revolution Rotation Tilt of Earth’s axis Axial parallelism Sphericity

Reasons for Seasons Revolution Earth revolves around the Sun Voyage takes ? Earth’s speed is 107,280 kmph (66,660 mph) Rotation Earth rotates on its axis once every ? hours Rotational velocity at equator is 1674 kmph (1041 mph)

Revolution and Rotation Figure 2.13

Reasons for Seasons Tilt of Earth’s axis Axis is tilted 23.5° from plane of ecliptic Axial parallelism Axis maintains alignment during orbit around the Sun North pole points toward the North Star (Polaris) Sphericity

Axial Tilt and Parallelism Figure 2.14

Earth-Sun Relations

Annual March of the Seasons Winter solstice – December 21 or 22 Subsolar point Tropic of Capricorn Spring equinox – March 20 or 21 Subsolar point Equator Summer solstice – June 20 or 21 Subsolar point Tropic of Cancer Fall equinox – September 22 or 23 Subsolar point Equator

The Egg and the Equinox Bad Astronomy: Only on the day of the Vernal (spring) Equinox, can you stand a raw egg on its end. Good astronomy: If you can stand a raw egg on end, it has nothing to do with the Equinox.

The Tides What are tides? Tides are periodic rises and falls of large bodies of water. What causes tides? Gravitational pull of the moon and the sun.

The Tides

1. Spring Tides2. Neap Tides

The Tides