AST 1002 Chapter 3
An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun?
8 years We need to find p so that p2 = a3. Since a = 4, a3 = 43 = 64. Therefore, p = 8, p2 = 82 = 64.
How did Copernicus challenge the Earth-centered model
Proposed a Sun-centered model (published 1543) Used model to determine layout of solar system (planetary distances in AU) But . . . The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles.
How did Galileo solidify the Copernican revolution?
Galileo overcame major objections to the Copernican view. Three key objections rooted in Aristotelian view were: Earth could not be moving because objects in air would be left behind. Non-circular orbits are not "perfect" as heavens should be. If Earth were really orbiting Sun, we'd detect stellar parallax
Overcoming the first objection (nature of motion):
Galileo's experiments showed that objects in air would stay with Earth as it moves. Aristotle thought that all objects naturally come to rest. Galileo showed that objects will stay in motion unless a force acts to slow them down (Newton's first law of motion).
Hallmark of Science: #2
Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (Simplicity = "Occam's razor")
Does astrology have any scientific validity?
Scientific tests have shown that astrological predictions are no more accurate than we should expect from pure chance.
Egyptian obelisk
Shadows tell time of day
Overcoming the third objection (parallax):
Tycho thought he had measured stellar distances, so lack of parallax seemed to rule out an orbiting Earth. Galileo showed stars must be much farther than Tycho thought — in part by using his telescope to see the Milky Way is countless individual stars. If stars were much farther away, then lack of detectable parallax was no longer so troubling
Overcoming the second objection (heavenly perfection):
Tycho's observations of comet and supernova already challenged this idea. Using his telescope, Galileo saw: Sunspots on Sun ("imperfections") Mountains and valleys on the Moon (proving it is not a perfect sphere)
Hallmark 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.
Darwin's theory of evolution by natural selection meets all the criteria of a scientific theory. This means:
After more than 100 years of testing, Darwin's theory stands stronger than ever, having successfully met every scientific challenge to its validity.
What is an ellipse?
An ellipse looks like an elongated circle.
Kepler's Second Law
As a planet moves around its orbit, it sweeps out equal areas in equal times. This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.
How is astrology different from astronomy?
Astronomy is a science focused on learning about how stars, planets, and other celestial objects work. Astrology is a search for hidden influences on human lives based on the positions of planets and stars in the sky.
How did Tycho, challenge the Earth-centered model?
Compiled the most accurate (one arcminute) naked eye measurements ever made of planetary positions. Still could not detect stellar parallax, and thus still thought Earth must be at center of solar system (but recognized that other planets go around Sun). Hired Kepler, who used Tycho's observations to discover the truth about planetary motion.
Many of our current systems had their roots in the achievements of ancient astronomy
Daily timekeeping Tracking the seasons Calendar Monitoring lunar cycles Monitoring planets and stars Predicting eclipses And more...
How can we distinguish science from non-science?
Defining science can be surprisingly difficult. Science from the Latin scientia, meaning "knowledge." But not all knowledge comes from science.
Underpinnings of the Greek geocentric model
Earth at the center of the universe Heavens must be "perfect": Objects moving on perfect spheres or in perfect circles
Why does modern science trace its roots to the Greeks?
Greeks were the first people known to make models of nature. They tried to explain patterns in nature without resorting to myth or the supernatural.
What was Galileo's role in solidifying the Copernican revolution?
His experiments and observations overcame the remaining objections to the Sun-centered solar system model.
How did Kepler challenge the Earth-centered model?
Kepler first tried to match Tycho's observations with circular orbits But an 8-arcminute discrepancy led him eventually to ellipses. "If I had believed that we could ignore these eight minutes [of arc], I would have patched up my hypothesis accordingly. But, since it was not permissible to ignore, those eight minutes pointed the road to a complete reformation in astronomy."
Hallmark of Science: #1
Modern science seeks explanations for observed phenomena that rely solely on natural causes. (A scientific model cannot include divine intervention)
Kepler's Third Law
More distant planets orbit the Sun at slower average speeds, obeying the relationship p^2 = a^3 p = orbital period in years a = avg. distance from Sun in AU
How was Greek knowledge preserved through history?
The Muslim world preserved and enhanced the knowledge they received from the Greeks. Al-Mamun's House of Wisdom in Baghdad was a great center of learning around A.D. 800. With the fall of Constantinople (Istanbul) in 1453, Eastern scholars headed west to Europe, carrying knowledge that helped ignite the European Renaissance.
Ptolemaic model
The most sophisticated geocentric model was that of Ptolemy (A.D. 100-170) — the Ptolemaic model: Sufficiently accurate to remain in use for 1,500 years. Arabic translation of Ptolemy's work named Almagest ("the greatest compilation")
Kepler's First Law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
What is a scientific theory?
The word theory has a different meaning in science than in everyday life. In science, a theory is NOT the same as a hypothesis, rather: A scientific theory must: Explain a wide variety of observations with a few simple principles, AND Must be supported by a large, compelling body of evidence. Must NOT have failed any crucial test of its validity.
Foci
focus point of an ellipse
paradigm
general pattern of thought
Major axis
long axis of an ellipse
perihelion
planet's closest point to sun (Greek)
aphelion
planet's most distant point from sun (greek)
eccentricity
quantity that describes the amount by which an ellipse is stretched out compared to a perfect circle
