This document provides an overview of the history and development of astronomy. It describes some of the key figures throughout history and their contributions, including: - Plato and Aristotle, who proposed early models of the universe with Earth at the center - Aristarchus, who first proposed a heliocentric model of the solar system - Copernicus, who revived Aristarchus' heliocentric theory - Kepler, who discovered his three laws of planetary motion providing strong evidence for the heliocentric model - Galileo and Newton, who provided further evidence for the heliocentric model and proposed gravity as the force governing planetary motion.

1. WHAT IS
ASTRONOMY?

2. • Astronomy is a science that encompasses the
study of all extraterrestrial objects and
phenomena.
• It is the science of space beyond Earth’s
atmosphere.
• Derived from the Greek root astron for star, and
nomos for arrangement or law.

3. ASTRONOMERS AND
THEIR CONTRIBUTIONS

4. PLATO /play·tow/
• 427 BC to 347 BC
• believed that the universe was
made of five types of matter: earth,
air, fire, water, and cosmos
• posited the shapes of the building
blocks of the universe. According to
him, the earth was formed of cubes

5. ARISTOTLE /eh·ruh·staa·tl/
• 384 BC to 322 BC
• believed the Earth was round
• first to attempt to create a scientific
model of the universe
• He believed that the Earth was the
center of the universe and the Sun,
Moon, planets, and all the fixed stars
revolved around it.

6. ARISTOTLE UNIVERSE

7. ADDITIONAL FACTS:
• He was an admired pupil of famed olden Greek
philosopher Plato.
• Aristotle tutored Alexander the Great and also taught
Ptolemy and Cassander, who were both eventually
crowned kings.
• While he was still alive he was known as “the man
who knew everything“.
• Aristotle was the father of Physics and Astronomy
and the founder of zoology.

8. ARISTARCHUS /eh·ruh·staar·kuhs/
• About 310 BC to 230 BC
• Most noted for proposing the idea of a
heliocentric universe with the earth as
one of the planets 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

9. ERATHOSTHENES /eh·ruh·taas·thuh·neez/
• 276 BC to 194 BC
• Developed a calendar with a leap
year.
• Measured the circumference of the
Earth in 325 BC and achieved an
accuracy of about 90% of the actual
number

10. HIPPARCHUS /huh·paar·kuhs/
• 190 BC to 120 BC
• consider the first great astronomer
and scientist
• Based on measurements during an
eclipse, he is able to place a range on
the distance to the moon.
• He estimated it to be between 59 and
67 Earth diameters. The actual
number is 60.

11. PTOLEMY /TOLL-uh-mee/
• About 85 AD to 165 AD
• Great proponent of the geocentric model
now known as the Ptolemaic system
• He is a great admirer of Hipparchus and
his rigorous method of verifying ideas
with empirical data

12. PTOLEMAIC SYSTEM

13. NICOLAUS COPERNICUS
• February 19, 1473 - May 24, 1543
• proposed his theory that the planets
revolved around the sun – Heliocentric
System
• Earth is a planet that besides orbiting
the Sun annually, also turns once daily
on its own axis

14. COPERNICAN MODEL

16. TYCHO BRAHE
• December 14, 1546 - October 24, 1601
• well known for his accurate and detailed
measurements of astronomical objects
• He combined the ideas of Ptolemy and
Copernicus with his own accurate
measurements to create a new geo-
heliocentric model.

17. BRAHE MODEL

19. JOHANNES KEPLER
• December 27, 1571 - November 15, 1630
• Discovered three major laws of
planetary motion
• His conclusions about the universe were
aligned with Copernicus’ model that had
the six known planets orbiting the Sun

20. KEPLER’S THREE LAWS OF
PLANETARY MOTION
(1) planets move in elliptical orbits with the Sun as a focus,

21. A MAJOR AXIS A MINOR AXIS
SEMI-MAJOR AXIS
Perihelion Aphelion
AN ELLIPSE ALSO HAS…
• Perihelion: When a planet is closest to the sun
• Aphelion: When a planet is farthest from the sun

22. (2) a planet covers the same area of space in the same amount of
time no matter where it is in its orbit
Faster when closer to the sun
Slower when farther from the sun

23. (3) a planet's orbital period is proportional to the size of its orbit
(its semi-major axis).

24. WHAT DOES THIS MEAN?
• If you know the distance from the sun and the year of planet A,
and you know the distance from the sun for planet B you can
find the year of planet B.
OR
• If you know the distance from the sun and the year of planet A
and planet B, you can find the distance from the sun for planet
B.

25. WHEN WE COMPARE THE ORBITS OF THE PLANETS
Planet P(yrs) a(au) P2 a3
Venus 0.62 0.72 0.38 0.37
Earth 1.00 1.00 1.00 1.00
Mars 1.88 1.52 3.53 3.51
Jupiter 11.86 5.20 141 141

26. GALILEO GALILEI
• February 15, 1564 - January 8, 1642
• First to point the refracting TELESCOPE
towards the heavens
• Studied the movement and orbits of many
nearby planets in our solar system
• Offered PROOF to Copernicus’s
Heliocentric Model of our Universe.
• Led to the discovery of the moons of
Jupiter

28. ISAAC NEWTON
• December 25, 1642 - March 20, 1727
• Proposed that all objects in the Universe
pulled on each other through gravity
• 3 laws of motion explain how the inertia
of a planet with gravity causes orbital
motion.
• Also, developed the reflecting telescope.

29. PREPARED BY:
Ms. Lianne Grace S. Parreñas, LPT