ANCIENT ASTRONOMY Chapter 1

ANCIENT ASTRONOMY In the British Isles, stones were used to keep track of the Sun and Moon. In the British Isles, stones were used to keep track of the Sun and Moon. Stonehenge

ANCIENT ASTRONOMY The Chinese developed a working calendar and kept careful track of comets, eclipses sun spots and variable objects The Chinese developed a working calendar and kept careful track of comets, eclipses sun spots and variable objects Early Chinese Star Chart

ANCIENT ASTRONOMY The Mayans also developed a very accurate calendar, later adopted by the Aztecs. The Mayans also developed a very accurate calendar, later adopted by the Aztecs. The Mayan culture was able to accurately predict solar and lunar eclipses. The Mayan culture was able to accurately predict solar and lunar eclipses. This structure, called the Caracol, at Chitzen Itza may have been used as a Venus Observatory This structure, called the Caracol, at Chitzen Itza may have been used as a Venus Observatory Dresden Codex Aztec Calendar The Caracol

EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC) Shape of Earth (circa 400 BC)

LUNAR ECLIPSE GEOMETRY

LIGHT RAYS FROM THE SUN

LUNAR ECLIPSE

Shape Earth: Erastothenes’ Method Shape Earth: Erastothenes’ Method

EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC) Shape of Earth (circa 400 BC) Size of Earth (Erastothenes circa 200 BC) Size of Earth (Erastothenes circa 200 BC) l 7/360 = AS/Circumference l AS = (5000 Stadia) 800 km l Circumference = 40,000 km Knowing  Knowing  l Radius = 6370 km

FLASHCARDFLASHCARD SUPPOSE THAT ERASTOTHENES HAD MEASURED THAT THE SUN WAS OVERHEAD AT SYENE AND 9 DEGREES AWAY FROM OVERHEAD AT ALEXANDRIA. WHAT WOULD HE HAVE CONCLUDED FOR THE RADIUS OF EARTH IF THE SYENE-ALEXANDRIA DISTANCE WAS 1200 KM? A) 7639 km B) 15,278 km C) 24,000 km D) 48,000 km

EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC) Shape of Earth (circa 400 BC) Size of Earth (Erastothenes circa 200 BC) Size of Earth (Erastothenes circa 200 BC) Relative Size of Earth and the Moon (Aristarchus circa 280 BC) Relative Size of Earth and the Moon (Aristarchus circa 280 BC) l From lunar eclipse ~1/3

LIGHT RAYS from the SUN

LUNAR ECLIPSE

EARLY GREEK ASTRONOMY Shape of Earth (circa 400 BC) Shape of Earth (circa 400 BC) Size of Earth (Erastothenes circa 200 BC) Size of Earth (Erastothenes circa 200 BC) l Relative Size of Earth and the Moon (Aristarchus circa 280 BC) l Size of the Moon, Distance to the Moon l Radius = 1730 km (0.27 Earth) l Distance = 380,000 km – from size and angular size

EARLY GREEK ASTRONOMY l Shape of Earth (circa 400 BC) l Size of Earth (Erastothenes circa 200 BC) l Relative Size of Earth and the Moon (Aristarchus circa 280 BC) l Size of the Moon, Distance to the Moon l Distance to the Sun

EARLY GREEK ASTRONOMY l Angular size Sun, Moon did not change (circular) l cos X = D moon /D sun l D moon already known – measure X - failed l X close to 90 o – if 90 Sun infinitely far away l Modern X = 89 o 51’ Sun 380 times farther than Moon X

HELIOCENTRIC SOLAR SYSTEM  Sun is much farther from Earth than the Moon (380 times farther)  Since the Sun and Moon have the same angular size, Sun is 380 times larger than Moon  Earth is 3 times larger than the Moon, thus the Sun is 100 times larger than Earth  Thus, the Sun is much more massive than Earth (assumes both have about the same density)  Hence, the Greeks concluded the the Sun is at the centre of the system (circa 200 BC) l Greek Argument that the Sun is at the Centre of the Solar System