Download Understanding the Development of Hellenistic and Copernican Cosmological Models - Prof. Ti and more Study notes Astronomy in PDF only on Docsity! EVENING LABS @ 6:30, not 6:00 model develop an explanation of how/why for the observation or experiment. use geometry, math, "cause & effect" Models must be testable they must make predictions that can be checked by observation or experiment. (This idea being testable also means that observations/experiments can be repeated by other observers.) Models may be disproved by making wrong predictions and not standing up under testing. Models cannot be proved only verified; the goal is not "right vs. wrong," but "accurate vs. inaccurate." hypothesis a model that has had little or no testing theory a model that has been tested many times and found to accurately explain many phenomena law a model that has been tested many, many times and found to accurately describe a great many phenomenato the point that we accept it to hold universally. Predict A scientific model will imply specific natural phenomena or consequences that can be tested. This means that more observation and experimentation will be done. Occam's Razor If there is more than 1 satisfactory model to explain some phenomenon, choose the simplest one. Title: May 12 9:02 AM (1 of 10) We have all these observations of the movements of the heavens. Can we develop a model that accurately describes these motions? Geocentric model of Ptolemy (c 140 AD) geocentric Earth fixed at the center. He refined the concept of an epicycle & deferent to explain retrograde motions of the planets. All planets (and the Sun & Moon) orbit the Earth. A planet actually moved on a small circle an epicycle that was centered on the larger, main orbit the deferent. (You get the brightness variation associated with retrograde motion "for free." Title: May 12 9:51 AM (2 of 10) So, in 1550, we had 2 equallyvalid models of the cosmos based on mutuallyexclusive ideas. Both do a good job of accurately predicting/modeling the motions of the heavens as good as any measurements available at the time. How can you tell which one is the better model? You need better data. Enter Tycho Brahe In the last quarter of the 16th century (15761597), Tycho made careful observations of the planets' motionaccurate to 1' Neither Ptolemy's model nor Copernicus' model could predict the positions of the planets to this precision. Johannes Kepler (literally) inherited Tycho's data/observations. Kepler was able to develop a model that was much more accurate than Ptolemy's or Copernicus'. It is stated in his 3 laws of planetary motion. Title: May 12 11:02 AM (5 of 10) Kepler's 1st Law (of Planetary Motion)(1609)
Each planet orbits the Sun following an ellipse with the Sun <
one focus of the ellipse.
Major axis
Semimajor axis Semimajor axis
The geometry of an ellipse
2nd Law (1609)
A line drawn from the Sun to a planet covers the same area
in a given time regardless of where the planet is in its orbit.
"Closer to the Sun = moving faster
Farther from the Sun = moving slower"
Example: An asteroid orbits the Sun with an orbit whose
semimajor axis is 9.0 AU. How long does it take to orbit th
Sun?
a:4oAe =) a +721
Pi!
| Pfr
P: 4024
? © 2°) Yeers
Attachments
