Chapter 22: Origin of Modern Astronomy

1. Chapter 22: Origin of Modern Astronomy Section 1: Early Astronomy Section 2: The Earth-Moon-Sun System Section 3: Earth’s Moon

2. Section 2: The Earth-Moon-Sun System • The two main motions of the Earth are rotation and revolution • Revolution-the movement of the Earth, in its orbit, around the sun • Rotation-the earth spinning on its access • Solar day- 24h, time it takes the Earth to rotate from noon to noon • Sidereal day- 23 hours 56 min, time it takes Earth to rotate from one star and back.

3. Revolution • Moves 107,000 km per hour around the sun. • Average distance is 150 million km • Perihelion- when earth is closest to the sun. January 3 (147 million km) • Aphelion- when the earth is furthest. July 4 (152 million km)

4. Earth’s Axis and Seasons • Earth’s axis is tilted 23.5 degrees • Due to this tilt, we experience seasons.

5. Precession • Motion of Earth’s axis as it traces out a circle on the sky. • Varies between 21.5 and 24.5 degrees. • Currently we point to the North Star Polaris • In about 1300 years, it will point to Vega. • The complete cycle takes 26,000 years

8. Motions of the earth-Moon System solstice • Perigee- when the moon is closest to the Earth • Apogee- when the moon is farthest from the Earth.

9. Phases of the Moon • See Figure 15 on page 626 (will be on test) • The change of the moons appearance as it rotates around the earth. • Starts with new • Waxing-the move from new to full • Waning- The move from full to new • Crescent- or ¼ moon • Gibbous- or ¾ moon • Caused by the changes in how much of the sunlit side of the moon faces earth.

11. Lunar Motions • Synodic month- the cycle of the moon through its phases. It takes 29.5 days • Sidereal month- the time it takes the moon to orbit around the earth once or 27.9 days. • The same side of the moon always faces the earth. • Its orbit is inclined by 5 degrees

12. Eclipses • Solar Eclipse- when the moon moves in the path directly between Earth and the sun. • Lunar eclipse- moon is eclipsed when it moves within Earth’s shadow. • During a new moon or full moon phase, the moon’s orbit must cross the plane of the ecliptic for an eclipse to take place. • See Figure 17 on page 628

13. Section 3: Earth’s Moon • The moon is less dense than the earth. • It has a small iron core. • Gravity is only 1/6 of that on the earth.

14. The Lunar Surface • Two types of land • Dark lowlands, and bright highlands • Maria-Latin for sea, describes dark areas • Craters- round depressions in the surface of the moon. • Formed from meteoroids or space junk

15. continued • See fig. 19 for crater formation • Lack of an atmosphere allows the moon to be bombarded. • Meteors 3m in diameter can create craters 150 meteors wide • Rays-outward splash marks from the craters

16. Highlands • Contains the mountains and large flat areas. • It is the pitted light colored areas.

17. Maria • Dark smooth areas where magma covered the moon’s surface. • Singular-mare, plural maria • Formed by striking asteroids early in the moon’s history. • Riles- look like valleys or trenches that may have carried lava.

18. Regolith • The layer of grey debris on the moon. • The remains of pulverized surface and meteorites

19. Lunar History • Around 4.5 billion years ago, an asteroid the size of Mars struck Earth. • It ejected tons of Earth’s crust and mantle into space. • There it collected together and formed the moon.

20. continued • After the moon formed, it was left to itself and it slowly cooled over time. • It was bombarded by debris and meteorites, leaving its surface speckled. • The moon was struck by several large asteroids forming the giant basin craters on its surface