© 2014 Pearson Education, Inc. The Science of Astronomy

© 2014 Pearson Education, Inc. 3.1 The Ancient Roots of Science Our goals for learning: –In what ways do all humans use scientific thinking? –How is modern science rooted in ancient astronomy?

© 2014 Pearson Education, Inc. In what ways do all humans use scientific thinking? Scientific thinking is based on everyday ideas of observation and trial-and-error experiments.

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? Many of our current systems had their roots in the achievements of ancient astronomy –Daily timekeeping –Tracking the seasons –Calendar –Monitoring lunar cycles –Monitoring planets and stars –Predicting eclipses –And more…

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? Ancient people of central Africa (6500 BC) could predict seasons from the orientation of the crescent Moon.

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? Days of week were named for the Sun, Moon, and visible planets.

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? Egyptian obelisk: Shadows tell time of day.

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? England: Stonehenge (completed around 1550 B.C.)

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? England: Stonehenge (1550 B.C.)

© 2014 Pearson Education, Inc. Mexico: Model of the Templo Mayor How is modern science rooted in ancient astronomy?

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? New Mexico: Anasazi kiva aligned north-south

© 2014 Pearson Education, Inc. SW United States: "Sun Dagger" marks summer solstice How is modern science rooted in ancient astronomy?

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? Scotland: 4,000-year-old stone circle; Moon rises as shown here every 18.6 years.

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? Peru: Lines and patterns, some aligned with stars.

© 2014 Pearson Education, Inc. Macchu Pichu, Peru: Structures aligned with solstices. How is modern science rooted in ancient astronomy?

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? South Pacific: Polynesians were very skilled in art of celestial navigation.

© 2014 Pearson Education, Inc. How is modern science rooted in ancient astronomy? France: Cave paintings from 18,000 B.C. may suggest knowledge of lunar phases (29 dots)

© 2014 Pearson Education, Inc. Bone or tortoise shell inscription from the 14th century BC. "On the Xinwei day the new star dwindled." "On the Jisi day, the 7th day of the month, a big new star appeared in the company of the Ho star." How is modern science rooted in ancient astronomy? China: Earliest known records of supernova explosions (1400 B.C.)

© 2014 Pearson Education, Inc. What have we learned? In what ways do all humans use scientific thinking? –Scientific thinking involves the same type of trial and error thinking that we use in our everyday live, but in a carefully organized way. How is modern science rooted in ancient astronomy? –Many of our modern timekeeping systems have ancient roots

© 2014 Pearson Education, Inc. 3.2 Ancient Greek Science Our goals for learning: –Why does modern science trace its roots to the Greeks? –How did the Greeks explain planetary motion?

© 2014 Pearson Education, Inc. Artist's reconstruction of the Library of Alexandria. 3.2 Ancient Greek Science

© 2014 Pearson Education, Inc. Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or the supernatural. Greek geocentric model (c. 400 B.C.) Why does modern science trace its roots to the Greeks?

© 2014 Pearson Education, Inc. Special Topic: Eratosthenes Measures Earth (c. 240 B.C.) Measurements: Syene to Alexandria distance ≈ 5000 stadia angle = 7° Calculate circumference of Earth: 7/360  (circum. Earth) = 5000 stadia  circum. Earth = 5000  360/7 stadia ≈ 250,000 stadia Compare to modern value (  40,100 km): Greek stadium ≈ 1/6 km  250,000 stadia ≈ 42,000 km

© 2014 Pearson Education, Inc. How did the Greeks explain planetary motion? Underpinnings of the Greek geocentric model: –Earth at the center of the universe –Heavens must be "perfect": Objects moving on perfect spheres or in perfect circles.

© 2014 Pearson Education, Inc. But this made it difficult to explain apparent retrograde motion of planets… Review: Over a period of 10 weeks, Mars appears to stop, back up, then go forward again.

© 2014 Pearson Education, Inc. Ptolemy But this made it difficult to explain apparent retrograde motion of planets… The most sophisticated geocentric model was that of Ptolemy (A.D ) — the Ptolemaic model: – Sufficiently accurate to remain in use for 1,500 years. – Arabic translation of Ptolemy's work named Almagest ("the greatest compilation")

© 2014 Pearson Education, Inc. But this made it difficult to explain apparent retrograde motion of planets… So how does the Ptolemaic model explain retrograde motion? Planets really do go backward in this model..

© 2014 Pearson Education, Inc. Thought Question Which of the following is NOT a fundamental difference between the geocentric and Sun-centered models of the solar system? A.Earth is stationary in the geocentric model but moves around Sun in Sun-centered model. B.Retrograde motion is real (planets really go backward) in geocentric model but only apparent (planets don't really turn around) in Sun-centered model. C.Stellar parallax is expected in the Sun-centered model but not in the Earth-centered model. D.The geocentric model is useless for predicting planetary positions in the sky, while even the earliest Sun-centered models worked almost perfectly.

© 2014 Pearson Education, Inc. Thought Question Which of the following is NOT a fundamental difference between the geocentric and Sun-centered models of the solar system? A.Earth is stationary in the geocentric model but moves around Sun in Sun-centered model. B.Retrograde motion is real (planets really go backward) in geocentric model but only apparent (planets don't really turn around) in Sun-centered model. C.Stellar parallax is expected in the Sun-centered model but not in the Earth-centered model. D.The geocentric model is useless for predicting planetary positions in the sky, while even the earliest Sun-centered models worked almost perfectly.

History of Astronomy Early Astronomy –2500 BCE –Akkadians made the first astronomical observations and records. Chinese astronomers recorded the conjunction of bring planets at about the same time. © 2014 Pearson Education, Inc.

History cont. Early Astronomy –1800 BCE –Stonehenge was erected. Used to mark the summer solstice and Chinese, Babylonians, and Egyptians developed the first accurate calendars from astronomical observations. © 2014 Pearson Education, Inc.

History of Astronomy 1300 BCE Chinese astronomers chart stars positions and recorded eclipses of the Sun and the moon. 700 BCE Babylonians are able to accurately predict positions of planets. 400 BCE Chinese astronomers produce the earliest known atlas of comets. © 2014 Pearson Education, Inc.

Ancient Model of the World Egypt The Earth is flat, the sky is like a flat plate, supported at four places by mountains. The Sun is carried across the sky in a boat from east to west. At night, the Sun carried back to the east through the Underworld. © 2014 Pearson Education, Inc.

Ancient Model India The Earth is a circular disk, surrounded by the ocean. In the center of the world is a great mountain. The Sun goes around the mountain once a day. In the evening, the Sun goes behind the western side of the mountain. It travels behind the mountain at night, and comes out on the eastern side in the morning. © 2014 Pearson Education, Inc.

Ancient History China The sky is a round dome, surrounding a flat square-shaped Earth. The Sun travels in a big tilted circle. At night, the Sun is not under the Earth, but rather on the side of the Earth. © 2014 Pearson Education, Inc.

Ancient Model Greece Most ancient Greeks believed that the Earth floated in the ocean like a cork in water. One person, named Anaximander, thought that the Earth was a cylinder with a round top, floating in the air, the sky surrounded the Earth, and beyond the sky was a region of fire. The sun, moon, and stars were holes in the sky, through which the fire could be seen. © 2014 Pearson Education, Inc.

Ancient Models 497 BC Pythagoras Greek philosopher who developed a model of the universe, which placed the Earth at its center. Each of the “wanderers” rotated around the Earth on their own glass sphere. These wanderers, were the Sun, moon, Mercury, Venus, Mars, Jupiter, and Saturn. © 2014 Pearson Education, Inc.

Ancient Models 322 BC Aristotle –Greek philosopher who showed that the Earth was round. He pointed out that during a lunar eclipse the Earth casts a curved shadow, and that travelers going North or South saw different stars at night. © 2014 Pearson Education, Inc.

Aristotle: Earth casts a curved shadow, thus Earth is a sphere. © 2014 Pearson Education, Inc.

Ancient Model 230 BC Aristarchus Greek astronomer who incorrectly measured the distance to the Sun, but was one of the first to introduce the idea that the Earth revolves around the Sun. © 2014 Pearson Education, Inc.

Ancient Model 195 BC Eratosthenes Greek astronomer who accurately measured the diameter of the Earth. By using the angles of the shadows cast in wells in two different places on the first day of summer, and the distance between them, he was able to then calculate the circumference of the Earth, and from that, the diameter of the Earth. © 2014 Pearson Education, Inc.

Eratosthenes: How circumference was figured out. © 2014 Pearson Education, Inc.

Ancient Model 127 BC Hipparchus Greek astronomer who erected an observatory and compiled a star catalog of about 850 entries. Along with the star’s coordinates (altitude and azimuth). He set six categories for their apparent magnitudes. He also discovered, by comparing his observations with older observations, that the Earth was wobbling on its axis. © 2014 Pearson Education, Inc.

Ancient Model He accurately calculated that the Earth’s precession took about 26,000 years to go through one cycle. The moon and Sun’s gravitational pull causes this to happen. © 2014 Pearson Education, Inc.

Precession © 2014 Pearson Education, Inc.

Ancient History 140 AD Ptolemy Greek astronomer who developed an Earth centered, geometrical model of the solar system. Though complicated, it was accurate, and explained how some planets seemed to reverse themselves in orbit around the Earth. This retrograde motion was explained by an elaborate circle on circle system using equant points, epicycles, and deferents. © 2014 Pearson Education, Inc.

Ancient History Ptolemy’s model was accepted as the correct model of our solar system for over 1400 years (Until the 16 th century). Even though it was completely wrong. Ptolemy was the last great astronomer of the ancient world. © 2014 Pearson Education, Inc.