NATS 1745 Study Guide - Final Guide: Copernican Heliocentrism, Orbital Speed, Ellipse
Course CodeNATS 1745
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Chapter 5 Exam Review
1. What was Tycho Brahe's lifelong goal? Did he achieve his goal in his
lifetime? Who carried on his work to successful completion?
To find the true motion of the planets. No. Kepler
2. What celestial event did Tycho Brahe witness in 1563? What did he observe
about the date of this event, and what did it motivate him to do?
He saw Jupiter, Saturn and venus conjunct. He measured the coordinates of the
planets during the conjunction and he found that the coordinates predicted
by the Ptolemaic and Copernican models were wrong and the dates were
wrong for this conjunction as well. The Copernican date was off by 2 days
and the Ptolemaic was off by a month. It motivated him to find the true
motion of the planets.
3. What discovery did Tycho make about the supernova of 1572, and how did
it contradict Aristotelian beliefs about the heavens?
During his time it was believed that the stars lasted forever, they cant be born
or die. This new star followed the other stars in the constellation. This
implied that stars could appear and disappear. Therefore Aristotle was
wrong, not everything in the sky was eternal.
4. What is parallax? Describe (briefly) how it should affect our view of the
stars. Why can't we see stellar parallax with the naked eye?
The perceived shift of an object relative to its background due to the motion of
the observer. The more distant the object, the smaller its parallax. Lamppost
and building looks like its moved but really the observer has moved.
5. Why did Tycho Brahe believe that the Earth is motionless?
When he observed the stars he couldn’t detect parallax. The nearby stars should
appear to move past us faster than the distant stars. Even with his high
precision instruments, Tycho couldn’t detect the parallax of the stars.
6. What is an astronomical unit?
The distance between the Earth and the Sun ~150 million km
7. Describe the Tychonic system (i.e. what do the planets orbit around? Does
the Earth move? If so, how? Does the Sun move? If so, how?)
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