Lesson 2: The Ancient Roots, Ancient Greek, Copernican Revolution, Galileo, Newton, Nature of Science Flashcards
What are some of humanity’s connections to astronomy socially, philosophically, practically?
what was it used for/practiced
It was often practiced for practical reasons
1. In keeping track of time and seasons
→ For civil organizations (religious, agriculture, etc.)
2. In aiding navigation
How do we know ancient humans had a good grasp of the patterns of astronomy (sunrise/sunset/eclipses/etc)
what did the Egyptians exactly do to keep track of the Sun
Track the constellations that were ahead of the Sun
* Ex. These next 12 constellations need to rise for the Sun to come up again
Our 24 hour day/clock comes from the Egyptians trying to track when the sun is going to come up
Provide some basic examples from other cultures on how we know they understood astronomical ideas.
Egyptians and the Flood
Ancient Egyptians tracked the sky so they could predict when the Nile would flood;
Sirius: brightest star in the sky that rises in Summer
* When they see the star Sirius, they know the river will flood soon
The heliacal rise of Sirius: predicts Nile’s annual flood and therefore marks the New Year; occurs on July 20th
How was the size of the Earth first estimated in 240 BCE?
Eratosthenes (astronomer) took the distance between Syene to Alexandria to find Earth’s circumference
Sun was at 7° from zenith
or about 1/50 of a complete circle
What are the geocentric and heliocentric view of the universe? What did Plato and Aristotle believe? What did their model of the universe have trouble explaining?
Geocentric model: the earth as the center
* Plato and Aristotle both believed that earth is the centre
* didn’t explain the retrograde motion
Heliocentric model: the sun as the center
How was the motions of the planets explained in Ptolemy’s geocentric model?
explain Ptolemy’s model and the motion
The most sophisticated geocentric model was that of Ptolemy — the Ptolemaic Model
- the Ptolemaic model had each planet move on a small circle whose center moves around Earth on a larger circle
- showed that planets really (apparent motion) do go backwards model
How does stellar parallax motion prove that the Earth is moving?
define Parallax as well
Parallax: the perceived shift of an object relative to its background due to the observer’s motion
Stellar Parallax: the shift of stars due to Earth’s motion through space. Closer stars shift more than distant stars
* If earth is moving around the sun, so then stars should shift their positions
* so the geocentric model couldn’t explain why stars were getting closer
How did the rise of the Islamic world contribute to our understanding of astronomy?
vaguely
The rise of Islam and the Muslim world preserved and enhanced the knowledge that received from Greeks
What was the celestial realm?
Hint: heaven
Most ancient Greek philosophers believed the Moon, the Sun, the planets and the stars moved on crystal spheres surrounding an unmoving Earth
* The ‘celestial realm’ is where only ‘perfect’ forms such as spheres and circles are found
What is the Copernican revolution?
- purposed the Sun-centered model
shift in the field of astronomy from a geocentric understanding of the universe, centred around Earth, to a heliocentric understanding, centred around the Sun
What did Copernicus, Tycho, and Kepler contribute to our shift to a heliocentric view of the universe?
2 points (about circles)
○ Perfect circles around the sun is not true
○ Orbits don’t have to be circular
What are Kepler’s 3 laws of motion? Why are they so important?
Kepler’s First Law: Planets move in elliptical orbits with the Sun as a focus
Kepler’s Second Law: When a planet is closer to the Sun, it travels faster and travels slower when its farther from the Sun
Kepler’s Third Law: A planet’s orbital period is proportional to the size of its orbit
* the farther a planet is from the Sun, the longer the orbital period
How did Galileo contribute to our understanding of the universe?
what did he support
- supported the Sun was at the centre
Describe Galileo’s telescope observations and how they challenged the prevailing ideas of a geocentric universe.
aganist the second and third objection (Hint: Moon, Sun, and Stars)
For the second objection (Noncircular orbits are not “perfect” as heavens should be)
Using a telescope, Galileo saw:
* Mountains and valleys on the Moon (proving it is not a perfect sphere)
* Sunspots on the Sun .. “Imperfections”
For the third objection (If Earth were really orbiting the Sun, we should detect stellar parallax )
Using a telescope, Galileo saw:
* the Milky Way has countless individual stars
* Planets and stars looked very different under magnification
→ If stars remained point-like under magnification, they must be MUCH farther away than the planets, lack of detectable parallax was no longer so troubling
How did Galileo definitively prove that Ptolemy’s model was incorrect?
two main things (hint: Jupiter and Venus)
- Galileo’s Observations in Starry Messenger: Jupiter’s 4 brightest moons (showed that if Jupiter can move with its moons, so can Earth)
- Galileo saw gibbous Venus. This is only possible if Venus orbits the Sun, as in the Copernican or Tychonic system; impossible in the Ptolemaic Model, and therefore Ptolemy’s model is obsolete
