Exam 1 is Feb. 1 (next Tuesday) This will cover everything we have done so far Earth motions The celestial sphere and observations from Earth Seasons

Transcription

1 Ancient Astronomy

2 Exam 1 is Feb. 1 (next Tuesday) This will cover everything we have done so far Earth motions The celestial sphere and observations from Earth Seasons Phases of the Moon Eclipses Ancient Astronomy Nature of science Chapters 1, 2, and part of 3 from the textbook. Make sure you have completed the following Lecture Tutorials and that you understand them: Position, Ecliptic, Seasons, Cause of Moon Phases, Observing Retrograde Motion

3 What causes eclipses? The Earth and the Moon cast shadows. When either passes through the other s shadow, we have an eclipse.

4 When can eclipses occur? Lunar eclipses can only occur at full moon Lunar eclipses can be penumbral, partial, or total Lunar eclipse simulation

5 When can eclipses occur? Solar eclipses can occur only at new moon Solar eclipses can be partial, total, or annular Solar eclipse simulation

6 Why don t we have an eclipse at every new and full moon? The Moon s orbit is tilted by 5 to the ecliptic plane There are two eclipse seasons each year, with a lunar eclipse at new moon and a solar eclipse at full moon Eclipse seasons simulation

7 Two conditions must be met to have an eclipse It must be a full moon (for a lunar eclipse) or a new moon (for a solar eclipse) AND The Moon must be at or near one of the two points in its orbit where it crosses the ecliptic plane (its nodes).

8 Predicting Eclipses Eclipses recur with the 18 year, 11 1/3 day saros cycle, but the type and location may vary.

9 How did astronomical observations benefit ancient societies? Keeping track of time and seasons For practical purposes, including agriculture For religious and ceremonial purposes Aiding navigation

10 Planets Known in Ancient Times Mercury (bottom) Difficult to see; always close to the Sun in the sky Venus (above Mercury) Very bright when visible; morning or evening star Mars (middle) Noticeably red Jupiter (top) Very bright Saturn (above Mars) Moderately bright

11 Days of the week were named for the Sun, Moon, and visible planets.

12 Ancient people of central Africa (6500 B.C.) could predict seasons from the orientation of the crescent moon.

13 What did ancient civilizations achieve in astronomy? Daily timekeeping Tracking the seasons and calendar Monitoring lunar cycles Monitoring planets and stars Predicting eclipses And more

14 Egyptian obelisk: Shadows tell time of day.

15 England: Stonehenge (completed around 1550 B.C.)

16 Mexico: Model of the Templo Mayor

17 New Mexico: Anasazi kiva aligned north south

18 SW United States: Sun Dagger marks summer solstice

19 Scotland: 4000-year-old stone circle; Moon rises as shown here every 18.6 years.

20 Peru: Lines and patterns, some aligned with stars

21 Macchu Pichu, Peru: Structures aligned with solstices

22 South Pacific: Polynesians were very skilled in the art of celestial navigation.

23 France: Cave paintings from 18,000 B.C. may suggest knowledge of lunar phases (29 dots).

24 "On the Jisi day, the 7th day of the month, a big new star appeared in the company of the Ho star." "On the Xinwei day the new star dwindled." Bone or tortoiseshell inscription from the 14th century B.C. China: Earliest known records of supernova explosions (1400 B.C.)

25 Cosmogony A cosmogony is theory about ones place in the universe. A geocentric cosmogony is a theory that proposes Earth to be at the center of the universe. A heliocentric cosmogony is a theory that proposes the Sun to be at the center of the universe.

26 Which is the geocentric cosmogony and which is the heliocentric cosmogony? geocentric (Earth-centered) heliocentric (Sun-centered)

27 Pythagorean Universe time: about 550 bc first recorded attempt at rational explanation of heavens formed foundation for Greek astronomy

28 Philosophical Ideas The heavens represent perfection. The heavens are immutable. The circle is the perfect shape. All heavenly motions must be circular.

29 Pythagorean Model stars reside on stellar sphere stellar sphere rotates about axis in 23 hours 56 minutes Sun follows path called ecliptic going around Earth once in one year accounts for most observations!!

30 North Star Stellar Sphere How the Greeks modeled the heavens Axis of Rotation