Chapter 22 Section 1

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

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

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

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

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

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

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

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

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

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

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?

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

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.

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

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

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)

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?

Summary