1. Cycles of the Sky Chapter 3:

2. The Annual Motion of the Sun Due to Earth’s revolution around the sun, the sun appears to move through the zodiacal constellations. The Sun’s apparent path on the sky is called the Ecliptic. Equivalent: The Ecliptic is the projection of Earth’s orbit onto the celestial sphere.

3. Simulations To study for this chapter review the simulations listed on the web site.

4. The Seasons (I) The Earth’s equator is inclined against the ecliptic by 23.5 o. The different incidence angle of the sun’s rays is causing the seasons on Earth:

5. The Seasons (II)

6. The Seasons (III) Northern summer = southern winter Northern winter = southern summer

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

8. Astronomical Influences on Earth’s Climate (I) Factors affecting Earth’s climate: Eccentricity of Earth’s orbit around the Sun (varies over period of ~ 100,000 years) Precession (Period of ~ 26,000 years) Inclination of Earth’s axis versus orbital plane Milankovich Hypothesis: Changes in all three of these aspects are responsible for long-term global climate changes (ice ages).

9. Astronomical Influences on Earth’s Climate (II) Last glaciation End of last glaciation Polar regions receiving less than average energy from the sun Polar regions receiving more than average energy from the sun

10. Motions of the Planets Pluto Neptune Uranus Saturn Jupiter Mars Earth Venus Mercury All planets in almost circular (elliptical) orbits around the sun, in approx. the same plane (ecliptic). Sense of revolution: counter-clockwise (Distances and times reproduced to scale) The Moon is orbiting Earth in almost the same plane (Ecliptic).

11. Mercury appears, at most, ~28 0 from the sun. It can occasionally be seen shortly after sunset in the west or before sunrise in the east. Venus appears, at most, ~ 46 0 from the sun. It can occasionally be seen for at most a few hours after sunset in the west or before sunrise in the east. Apparent Motion of the Inner Planets

12. The Phases of the Moon (I) As the Moon orbits around Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the Moon.

13. The Tidally Locked Orbit of the Moon The moon is rotating with the same period around its axis as it is orbiting Earth (tidally locked). We always see the same side of the moon facing Earth.