Mr Ross Brown Brooklyn School for Law and Technology Aim How did early astronomers study our universe 21 March 2016 Do now What evidence do you have that our Earth is round Use nakedeye observations ID: 526738
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Slide1
Introduction to Classical Astronomy
Mr. Ross Brown
Brooklyn School for Law and TechnologySlide2
Aim: How did early astronomers study our universe?
21 March 2016
Do now: What evidence do you have that our Earth is round? Use “naked-eye” observations.Slide3
We knew the Earth was round
Pythagoras, 500 BC (
Before Christ, or BCE, Before Common Era
) suspected it
Aristotle (384-322 BC)
observed itNaked-eye observationsSlide4
Aim: How did early astronomers study our universe?
22 March 2016
Do now: Why does the Moon appear so much larger at the horizon? Why do the Sun and Moon appear similar in size in our sky?Slide5
Angular sizeSlide6
Ponzo Illusion
The human mind judges an object’s size based on its background.Slide7
Ebbinghaus IllusionSlide8
Angular size of Sun and MoonSlide9
Calculating the Earth’s Circumference
Eratosthenes
(276-195 BC)
Used measurement and geometry
Parallel lines and their
transversal (a line that passes through 2 parallel lines)Slide10
Eratosthenes’ calculationsSlide11
Relative sizes of Sun and Moon and Distances to Each
AristarchusSlide12
Homework
Provide examples of observational evidence that the Earth is round.Slide13
How did classical astronomers explain planetary motion?
Do now: How does the Earth’s motion through space compare to Mercury? Or to Mars? Is the Earth moving faster or slower?Slide14
The Planets
Ancient Greeks noticed five bright “stars” in the night sky that didn’t stay fixed like stars
We named them
planets
from the Greek word for “wanderers”
Planets seemed to move independently, so they were named after godsSlide15
Where is the center of the Solar System?
Geocentric: Earth is the center
Heliocentric: Sun is the centerSlide16
Retrograde Motion Worksheet
You can work with a partner
Please take your time and use care with this work.Slide17
A Flaw in the Geocentric Model
Retrograde Motion
: planets beyond Earth relative to Sun sometimes appear to move backwards. This is due to slower paths around Sun and being “lapped” by Earth.Slide18
Homework #5
What was Nicolaus Copernicus’ theory about the Solar System?
What did
Tycho
Brahe design and build?
What did Johannes Kepler learn about planetary orbits?Slide19
Aim: How did our study of the universe advance?
Do now: How did retrograde motion illustrate the likelihood of a heliocentric universe?Slide20
Nicolaus Copernicus (1473-1543)
Used retrograde motion to show that planets closer to the Sun overtake planets further away, indicating heliocentric model
Calculated distances to other planets based on an
astronomical unit
(AU)
Showed that the universe was much, much larger than thought. People began thinking other stars might be suns with other planets orbiting them.Slide21
Distance from Sun to its planets
(the universe is HUGE!!!)Slide22
Tycho
Brahe (1546-1601)
Danish astronomer, and wealthy. Used his power to design better telescopes and made great discoveries.Slide23
Johannes Kepler (1571-1630)
Brahe’s assistant. Used Brahe’s data to create an accurate picture of the path of Mars.
Not a circle, but an
ellipse
(a flattened circle.)
An ellipse has long and short dimensions, its major and minor axes
.
½ the major axis is referred to as the
semimajor
axis.Slide24
Kepler’s Three Laws
Planets move in elliptical orbits with the Sun at one focus of the ellipse
The planet’s orbital speed varies so a line joining the Sun and the planet will sweep equal areas in equal time intervals
There is a relationship between the time of a planet’s solar orbit and its orbit’s size, i.e., the square of the time to orbit (p
2
) is equal to the cube of the
semimajor
axis (a
3
)Slide25
Aim: How did our understanding of the universe continue to develop?
Do now: What keeps the planets of our solar system from colliding?Slide26
Galileo Galilei (1564-1642)
First person recorded to use telescope to study heavens
Saw mountains and features on Moon
Saw sunspots on the Sun
Saw objects orbiting Jupiter (which Kepler named ‘
satellites’)Got in trouble with the Church during the Inquisition. Forced to
recant
and held under house arrest for rest of his life.Slide27
Galileo Galilei (1564-1642)
https://commons.wikimedia.org/w/index.php?title=File%3AApollo_15_feather_and_hammer_drop.oggSlide28
Isaac Newton (1642-1727)
Contributions to math, physics, astronomy
First to truly understand importance of
gravity
as a forceSlide29
Homework
If an asteroid has an average distance from the Sun of 4 AU, what is its orbital period?