History of astronomy

1. Miss Witkowski History of astronomy

2. What is Astronomy • Astronomy- Study of celestial objects, space and the physical universe as a whole • Stars • Planets • Moons • Asteroids • Comets • Etc.

3. History of Astronomy Almost every culture throughout time has studied the universe Egyptians Saw patterns in the Sun, moon, and Venus Developed 365 day year solar calendar Mayans Built temples for worship Practiced astrology Chinese Earliest known atlas of comets

4. History of Astronomy • Eratosthenes (276 - 195 B.C.) • 1st person able to measure the circumference of the Earth • Came within a couple thousand miles of actual value • Used geometry and ratios to determine the size of Earth • Ptolemy (90 – 168 AD) • Worked out a complex system of Epicycles and perfect circles for the orbits of planets, sun, and moon around Earth • Geocentric Model– Earth is center of universe • Lasted for 1400 years

5. Geocentric Model

6. History of Astronomy Aristarchus • First proposed idea that Earth, as one of the planets, is moving around the Sun • First to attempt to measure the relative distance between the Earth-Moon and the Earth-Sun without the aid of trigonometry • Actual angle = 89°not 87°

7. History of Astronomy • Nicolas Copernicus- 1540 • 1stto propose a Heliocentric Model- • Planets and moons revolve around the Sun • Orbits still perfect circles with epicycles • Invented idea of Astronomical Unit (A.U.) – Distance of Earth from the Sun (About 93 million miles)

8. History of Astronomy Tycho Brahe – 1576 • Collected data of position of planets for 20 years • Able to make accurate predictions of positions without telescopes • Had own “Tychonic Universe” • Combination of Ptolemy & Copernicus • Earth is stationary • Believed in circular orbits

9. History of Astronomy Kepler Laws of Planetary Motion • 1st Law- Orbits are elliptical • 2nd Law- A line from a planet to the sun sweeps over equal areas in equal times • Planets travel at different speeds – due to pull of gravity • 3rd Law- the time it takes a planet to orbit the sun is related to how far away it is

10. History of Astronomy Galileo Galilei- Father of Modern Science • Born in 1564 • Supports Copernicus’ theory of heliocentric universe • Used telescope to observe: • Surface of Moon – was not perfect • Phases of Venus • Milky Way Galaxy was made up of many stars • Moons of Jupiter

11. Galileo Moon surface Phases of Venus

12. Isaac Newton • Born in 1654 (year Galileo dies) • Three Laws of Motion • Answered Kepler’s question of what keeps the planets in orbit • Gravity! • Gravitational force between two object decreases as the distance between the objects increases • More Mass = More Gravity

13. Geocentric or Heliocentric? • Of the early philosophers, only Hipparchus favored the heliocentric model • Most philosophers thought that the evidence supported the Geo model more than the Helio model • Everything appears to revolve around the Earth each day (makes sense for it to be at the center)

14. Problems with Geocentric Model • The planets appear to change brightness, implying a change of distance • The Sun, Moon, and Planets do not move at the same speed all the time • Mercury and Venus always appear close to the Sun

15. Evidence of the Heliocentric Model • The changing brightness of the planets is explained by the Earth getting closer and farther from the planets during our orbit of the Sun • Mercury and Venus are always close to the sun because they orbit the sun, just as we do • Stellar Parallax – As the Earth revolves around the sun, the closer stars shift among the background of further stars

16. Problems with the Heliocentric Model • We do not feel the Earth moving or the atmosphere being pulled away as we fly around the Sun • If the Earth were spinning, wouldn’t we be thrown off into space? • No, Gravity

17. So Which is Right? • The ancients favored the geocentric model because it seemed impossible to believe that the Earth was moving • During ancients times, the mathematical and scientific tools were not available to answer the question without dispute • At this time, modern Astronomy supports the Heliocentric Model