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
What is Newton’s universal law of gravitation?
* 3 laws
- Every mass attracts every other mass
- Attraction is directly proportional to the product of their masses
* Increase the mass of M1, the gravitational pull will be larger - Attraction is inversely proportional to the square of the distance between their centres
* Increase distance, the gravitational pull will be smaller
What is centre of mass?
The mass of the two objects determines their orbit which will create the centre of mass
* If earth was larger in mass, the centre of mass would be closer to earth, then planets closet will orbit around earth
Objects orbit around their centre of mass, where most of the mass is
How does Kepler’s 3rd law help us determine the mass of something in space?
Newton’s laws of gravity and motion showed that the relationship between the orbital period and average orbital distance of a system tells us the total mass of the system
- Earth’s orbital period (1 year) and average distance (1 au) tell us the Sun’s mass
- Orbital period and distance of a satellite from Earth tell us Earth’s mass
What is Mass? Gravity? Weight?
Mass: An object is the sum of all its atoms
Gravity: general force of attraction between all material bodies
Weight: the strength of gravity exerted by a planet (or moon, star, etc) on an object in the planet’s gravity field
What are Newton’s laws of motion?
- An object moves at constant velocity unless a net force acts to change its speed or direction
- The acceleration (a) of an object due to a force (F) is related to the object’s mass
- For every force, there is always an equal and opposite reaction force
What is science? what is non-science?
define hypothesis, scientific theory
Science: seeks explanations that rely solely on natural causes; progresses through the creation and testing of models of nature; models must make testable predictions
+ hypothesis: making an educated guess
+ scientific theory: is a fact; be supported by a compelling body of evidence, has NOT have failed any crucial test of its validity
What are some ‘hallmarks’ of science?
three hallmarks
Hallmarks of Science #1
* Modern science seeks explanations for observed phenomena that rely solely on natural causes
(A scientific model cannot include divine intervention)
Hallmarks of Science #2
* Science progresses through the creation and testing of models of nature that explain the observations as simply as possible
Hallmarks of Science #3
* A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations
What is the definition of cosmology?
Cosmology: the basic structure and origin of our structure of the cosmos
Why did Aristotle know that the Earth was round, over 2000 years ago?
two points (Hint: moon, traveling from north to south)
- The Moon enters or emerges form Earth’s shadow during an lunar eclipse - shape of shadow is always round
- He explained that travelers would go to the south and notice stars from the north were not visible anymore - traveller must have moved over a curved surface of the Earth
Which early Greek philosopher believed the Earth to be orbiting the Sun (ie, aheliocentric universe)?
Aristarchus of Samos
From Astronomy Basics, understand the three reasons why we know the Earth is spherical.
three points (ship, ISS, sun location)
- ships sinks below the horizon, with the hull disappearing first and the mast remaining visible for a while longer.
- the International Space Station circles Earth once every 90 minutes or so. Photographs taken from the shuttle and other satellites show that Earth is round from every perspective.
- the Sun would be high in the sky in other time zones the sun would be rising, setting, or completely out of sight
Explain how Eratosthenes was able to measure, not only that the Earth was round, but the size of the sphere of the Earth.
Hint: sun rays
Eratosthenes measured the size of Earth by observing the angle at which the Sun’s rays hit our planet’s surface.
Who is Hipparchus, and what is precession?
(hint: star brightness and make an discovery about earths axis)
Hipparchus, was a astronomer who divided the stars into apparent magnitudes: a stars ranked by their apparent brightness
Made the discovery: the position in the sky of the north celestial pole had altered over the previous century and a half
Precession: the direction in which Earth’s axis points does indeed change slowly but regularly
define Retrograde motion
The temporary apparent westward motion of a planet as Earth swings between it and the Sun
How did Ptolemy’s model of the universe (a geocentric model) explain the apparent retrograde motion of planets on the sky?
he created the Epicycle: a circle in which a planet moves and which has a center that is itself carried around at the same time on the circumference of a larger circle
What is an ellipses major axis? what is its semimajor axis?
Major axis: widest diameter of the ellipse
Semimajor axis: the distance from the centre of the ellipse to on end
* Is equal to the planets average distance to the sun
What are the positions of the two pins affects the size/shape/ellipticity of the ellipse.
Two points inside the ellipse are called its foci (singular: focus)
* The ‘roundness’ of the eclipse depends on how close the foci are compared to these axis
What is orbital speed?
Orbital speed: the speed of each planet along with the ellipse
What is momentum?
mass in motion, not likely to stop / remains unchanged
What is inertia?
matter that is moving unless an external unbalanced force acts upon it
What is angular momentum? What is the conservation of angular momentum?
Angular Momentum: a measure of rotation of a body as it revolves around some point
* As a planet approaches the Sun on its elliptical orbit and the distance to the spin center decreases, the planet speeds up to conserve the angular momentum. Similarly, when the planet is farther from the Sun, it moves more slowly.
Conservation of Angular Momentum: an object’s spin remains constant unless an external torque acts upon it
Torque: force that can cause an object to rotate about an axis
