1. Lunar Phases, Eclipses and Seasons Physics 102 Goderya Astronomy

2. The Phases of the Moon From Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the Moon.

3. Lunar Eclipses Earth’s shadow consists of a zone of partial shadow, the Penumbra, and a zone of full shadow, the Umbra. If the moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse. If the entire surface of the moon enters the Umbra, the lunar eclipse is total.

4. A Total Lunar Eclipse

5. Why the Red Glow? A total lunar eclipse can last up to 1 hour and 40 min. During a total eclipse, the moon has a faint, red glow, reflecting sun light scattered in Earth’s atmosphere.

6. Solar Eclipses The sun appears approx. as large in the sky (same angular diameter ~ 0.5 0 ) as the moon.  When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse.

7. Total Solar Eclipse Prominences Chromosphere and Corona

8. Conditions for Eclipses Eclipses occur in a cyclic pattern.

9. Temperature & Sun Rays

10. The Cause for Seasons Earth’s axis of rotation is inclined vs. the normal to its orbital plane by 23.5°, which causes the seasons.

11. Season Markers The seasons due to inclination of spin axis Aphelion Perihelion January 3 July 4 September Equinox March Equinox December Solstice June Solstice

12. Sun Rays & Incidence Angle They are not related to Earth’s distance from the sun. In fact, Earth is slightly closer to the sun in (northern- hemisphere) winter than in summer. Light from the sun Steep incidence → Summer Shallow incidence → Winter The Seasons are only caused by a varying angle of incidence of the sun’s rays.

13. Daylight Hours Northern summer = southern winter Northern winter = southern summer

14. Variation of Daylight hours

16. Common Misconception Earth’s distance from the sun has only a very minor influence on seasonal temperature variations. Sun Earth in July Earth in January Earth’s orbit (eccentricity greatly exaggerated)