1. Chapter 22
Section 1

2. Astronomy: The First Science
Egyptians studied the motion of the sun 6,000-7,000 years ago!

3. Astrology?
You may have heard of astrology which links the 12 constellations that appear on the ecliptic (known as the signs of the zodiac) to a variety of things. Links are usually made to associate a persons personality with their “zodiac sign”
This practice is not a formally recognized scientific discipline and is not affiliated with the science of astronomy or astrophysics

4. Cultural Connection
Virtually every culture with a written language studied astronomy
The Babylonian’s kept very precise records of celestial events
The supernova that created the crab nebula was recorded by the Chinese in 1054
The Maya tracked the planets, especially Venus, with astonishing accuracy

5. Stonehenge Stonehenge was built by the Druids about 2,500 BC
How it was constructed remains a mystery because the people who built it did not have a written language
Constructed to keep time and track the summer and winter solstice

6. Why Astronomy?
Cultures needed to keep track of time and the seasons to plant and harvest crops properly

7. Greek Contributions to Astronomy
The ancient Greeks noted that some objects in the night sky did not remain in static position as did the rest of the stars
The Greeks called these objects “wanderers”
Planet is the Greek word for Wander

8. Aristotle
Concluded the Earth was round because it always casts a curved shadow on the moon during an eclipse

9. Eratosthenes
Calculated the circumference of the Earth by determining the angular difference in the height of the noon sun in two different cities

10. The Round Earth
The idea of the round Earth was largely abandoned during the Middle Ages

11. The Geocentric Model
Early astronomers, including Ptolemy and Aristotle, thought Earth was the center of the solar system.
This model explained many events very well
The geocentric model was used for over 1000 years

12. THINK – PAIR - SHARE
What is the difference between Astronomy and Astrology?
Why would ancient civilizations track the movement of the sun and moon?
Name some of the civilizations that had calendars.
Why would people place the Earth as the center of the solar system? What is it called?
How did the Greeks change perceptions?

13. Retrograde Motion
Planets do not move in a straight line across the sky throughout the year. Sometimes they reverse direction, and then reverse again!

14. Galileo Galilei Galileo made the first telescope
His observations of the moons of Jupiter and the phases of Venus in 1609 reveled problems within the geocentric model.

15. The Heliocentric Model
Copernicus moved the sun to the center of the model in 1543
This model still had the planets orbiting the sun in perfect circles
Kepler improved the heliocentric model by noting that elliptical orbits fit observable phenomena better

16. Newton
The heliocentric model explained that planets orbited the sun, but no one knew why
Isaac Newton explained that gravity held objects in their orbits
Newton explained that all objects in the universe follow the same rules
All classical physics are based on this assumption

17. Astronomical Units of Measure
Light year: The distance light travels in a vacuum in 1 year.
1 Ly = 9,460,730,472,580.8 km (Aprox 9.5 trillion)
Astronomical Unit: The average distance from the Earth to the sun.
149,597,870,691 meters (aprox. 150 million kilometers or 93 million miles)

18. THINK – PAIR - SHARE What is Retrograde motion?
How does this movement happen?
What did Newton have to do with the model of the Solar System?
Who made the first telescope and what did he use if for?
When do we use Astronomical Units instead of Light years?

19. Summary