HISTORY OF ASTRONOMY, PART 1. How our understanding of the Universe has changed

Transcription

1 HISTORY OF ASTRONOMY, PART 1 How our understanding of the Universe has changed

2 Focus Question: How and why has our understanding of the universe changed over time?

3 The oldest science? As far back as the stone and bronze ages, human cultures realized the cyclical nature of the motions in the sky. Monuments dating back to ~ 3000 BCE show alignments with astronomical significance. Those monuments may have been used as calendars or even as ancient observatories.

4 Stonehenge, England ( BCE) Alignments with locations of sunset, sunrise, moonset and moonrise at summer and winter solstices Possibly used as a calendar.

5 Pyramid of Khufu, Giza (Egyptian Culture, BCE) Shafts from the King's chamber indicate location of Polaris 5000 years ago Former position of Orion's belt The pyramid is also aligned perfectly N-S and E-W

6 Solstice and equinox alignments Star alignments Alignments with Venus Caracol Temple, Mexico (Mayan culture ~ 1000 CE)

7 Big Horn Medicine Wheel, Wyoming (Plains Indians, approx CE) alignments to the rising and setting of the Sun at summer solstice alignments to rising places of Aldebaran, Rigel, Orion, and Sirius (all bright stars associated with the Solstice)

8 Discussion: Do you think these monuments were intentionally aligned with objects in the sky, or is it just a coincidence? If it was intentional, how were these ancient cultures able to do this?

9 Early Astronomy

10 Mesopotamian Astronomy ~ 1200 BCE Earliest Babylonian star catalogues recorded observations on clay tablets Babylonian astronomy was the basis for much of what was done in Greek astronomy later

11 GRECO-ROMAN ASTRONOMY Identifying the structure of the universe

12 Major Greek Astronomers Aristotle ( B.C.E.) major authority in ancient Greece, promoted the idea of a geocentric universe and first principles Ptolemy ( C.E.) -- Wanted to create a mathematical model of the universe and explain retrograde (backward) motion of the planets

13 Astronomy in ancient Greece Greek models were based on first principles, believed to be obvious and not questioned: 1. Geocentric Universe: Earth at the center of the Universe. 2. Perfect Heavens : Motions of all celestial bodies described by motions involving objects of perfect shape, i.e., spheres or circles. 3. Unchanging Heavens : always was and always will be the same

14 Aristotle s model of the Universe Earth was at the center of the universe The heavens were literally composed of 55 crystalline spheres to which the celestial objects were attached Each sphere rotated at a constant velocity (although some spheres rotated faster than others)

15 Discussion: Based on your observations of the planetarium dome last week, did you see any evidence that could support Aristotle s model of the Universe?

16 Motions of the Wanderers The ancient Greeks tracked seven objects that seemed to move against the background of fixed stars in the sky: the Sun, the Moon, Venus, Jupiter, Saturn, Mercury, and Mars They named them planets (the Greek word for wanderers), Aristotle s model of the universe could not explain the motion of these wanderers, who sometimes even appeared to move backwards from one night to the next.

17 Ptolemaic Model of the Universe Ptolemy created a model that more accurately explained the motions of the sky, including the retrograde (backwards) motion of the planets Ptolemy s model became the standard used by scholars for 1,500 years because: It worked (almost)- It could predict the position of a planet to within 2. It accounted for the observed planetary motions, including retrograde motion and variations in brightness. It placed the Earth in its natural place at the center of things It matched with common sense. We do not feel the Earth move, and we can see the stars and planets move

18 Ptolemy s Epicycles naissance/marsorbit.html The Ptolemaic system (still geocentric) was considered the standard model up until the Renaissance!

19 History of Astronomy Essential Questions: How do astronomers study the universe? How can we make a model to help us understand our universe? How does technology affect our understanding of the universe?