History of Astronomy – Guided Notes
Part 1 Astronomy: The oldest science?
– As far back as the Stone and Bronze Ages, human cultures realized the cyclical nature of the
______________ in the sky
– Monuments dating back to ~3000 BCE show alignments with astronomical significance that
might have been used as _______________________ or ancient observatories
• Mesopotamian Astronomy ~ 1200 BCE
– Earliest Babylonian __________ catalogues recorded observations on clay tablets
– Babylonian astronomy was the basis for much of what was done in _____________
astronomy later
Greco-Roman Astronomy
• Major Greek Astronomers
– Aristotle (384-322 B.C.E.) – major authority in ancient Greece, promoted the idea of a
geocentric universe and _____________________________
– Eratosthenes (276 - 194, B.C.E.) – calculated the circumference of Earth using shadows and
trigonometry
– Ptolemy (85--165 C.E.) -- Wanted to create a mathematical model of the universe and
explain ___________________ (backward) motion of the planets
•
Astronomy in ancient Greece
– Greek models were based on “first principles”, believed to be _______________________
and not questioned:
•
______________________ Universe: Earth at the center of the Universe.
•
“Perfect Heavens”: Motions of all celestial bodies described by motions involving
objects of “perfect” shape, i.e., _________________ or circles.
•
“Unchanging Heavens”: always was and always will be the same
• Aristotle’s Model of the Universe
– Earth was at the ________________ of the universe
– The heavens were literally composed of 55 crystalline spheres to which the celestial objects
were attached
– Each sphere __________________ at a constant velocity (although some spheres rotated
faster than others)
• Motions of the “Wanderers”
– The ancient Greeks tracked __________ objects that seemed to move against the
background of fixed stars in the sky: the Sun, the Moon, Venus, Jupiter, _____________,
Mercury, and Mars
– They named them “planets” (the Greek word for wanderers), and Aristotle’s model could
not explain the motion of these wanderers who sometimes even appeared to move
backwards from one night to the next.
• 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! It could predict the __________________ of a planet to within 2°.
•
It accounted for the observed planetary motions, including retrograde motion and
variations in brightness.
•
It placed the _____________ 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
– Ptolemaic system of epicycles (still ________________________ ) was the “standard
model” up until the Renaissance
Part 2 Astronomy in the Renaissance
•
Nicolaus Copernicus (1473 – 1543)
– Polish lawyer, physician, and mathematician
– Studied the planets and proposed a new model for the universe
– His model caused controversy by “changing our place in the universe”, leading to what is
known as the Copernican Revolution
•
Copernican Model of the Universe
– The Heliocentric Universe
• ______________ at the center
•
Earth was a planet, and the _____________ revolved around Earth while the earth
revolved around the sun
•
Original model still accepted Aristotle’s ideas of uniform motion and circular orbits,
so it _________ __________ perfectly predict the motion of the planets
•
•
Arrangement of the Planets
– Copernicus made observations that allowed him to determine the ________________ of
the 5 planets known at that time
•
Mercury and Venus can only be observed fairly __________ to the sun at dawn or
dusk (their orbits must lie inside of Earth’s orbit, since they are always in the same
direction as the sun)
•
Mars, Jupiter and Saturn can be observed at night when the sun is far below the
horizon (only possible if _______________ is between the sun and these planets, so
they must lie outside Earth’s orbit)
•
By measuring the ___________ it took planets to return to the ______________
position in the sky, he determined their distances from the sun
Copernican explanation of retrograde motion in a heliocentric universe
– Retrograde (backward) motion of a planet occurs when the Earth “passes” the planet as
they both orbit the sun
Kepler and Galileo: Refining Heliocentric Cosmology
•
Johannes Kepler (1571-1630)
– Kepler used Tycho Brahe’s meticulous observations to deduce a
__________________________ explanation for the motion of the planets
– Determined that Copernicus made a ______________-- planets do not orbit the sun in
perfect circles!
•
Kepler’s Laws of Planetary Motion
1. The orbits of the planets are ellipses with the _________ at one focus
2. A line from a planet to the sun sweeps over equal areas in equal intervals of time.
3. A planet’s orbital period (P) squared is proportional to its average distance from the sun
(a) cubed
http://science.sbcc.edu/physics/flash/Keplers%20Laws.html
– Kepler’s First Law (orbital shapes)
 Orbits of planets are _________________________ with the sun at one focus
•
Eccentricity = how _________________________________ an ellipse is
•
Planet’s orbits are very close to circular with __________ eccentricities
– Kepler’s Second Law (changing speeds)

A line from a planet to the sun sweeps over ____________ areas in equal intervals
of __________________

Planets move ________________ when closer to the sun
– Kepler’s Third Law (length of years)
–
–

There is a mathematical relationship between the __________________ from the
sun and the _______________ it takes the planet to complete its orbit.

P 2 = a3
Galileo Galilei (1564- 1642)

Greatly improved upon the newly invented telescope and made discoveries in
________________ of the Heliocentric model of the solar system

Galileo discovered
•
Four _____________ of Jupiter
•
Surface structures on the moon (not a perfect _______________ )
•
Sun Spots
•
Phases of _______________, proving it orbits the Sun and not Earth
Conflict of Religion and Science

Galileo’s observations and evidence in support of the Copernican Theory created a
___________________ between a faith-based system and the scientific ways of
thinking based on observation and evidence

His methods and conclusions are considered the birth of the __________
__________________________________
Part 3: A New Era of Science
– Astronomy continued to evolve after the Renaissance
– Mathematics as a tool for understanding the _________________ of the universe became
the central focus
– Isaac Newton (1643 - 1727)

Added physics interpretations to the mathematical descriptions of astronomy by
Copernicus, Galileo and Kepler

Invented __________________ as a necessary tool to solve mathematical problems
related to motion

Discovered the three laws of _______________

Discovered the universal law of mutual _____________________
– Newton’s Laws of Motion

Newton’s 1st Law of Motion - A body at rest continues to rest, and a body in motion
will continue in uniform motion in a straight line unless it is acted upon by some net
force. (AKA- ____________________)

Newton’s 2nd Law of Motion - Acceleration (a) of a body is inversely proportional to
its mass (m), directly proportional to the net force (F), and in the same direction as
the net force. (F = m a)

Newton’s 3rd Law of Motion- to every action there is an equal and opposite
______________________
– Newton’s Universal Law of Gravity

More Mass = ____________ gravitational force

More Distance = _____________ gravitational force
– Mass vs. Weight

Your weight is a measure of the force of gravity acting on your body
•

Your weight will be _________________ on the moon
Your mass is a measure of how much matter you contain.
•
Your mass will be __________________ on the moon
– Newton’s Laws of Motion and Law of Universal Gravitation helped explain WHY the
planets move the way that they do