Mastering Astronomy Chpt. 3
The shadow cast by a simple stick or obelisk allowed ancient people to
tell the time of day
An original observation of Galileo's that helped to overturn the ancient Earth-centered model was
the phases of Venus
Orbital period around the sun depends on
the planet's average distance from the sun
A planet is discovered orbiting the star 51 Peg with a period of four days (0.01 years). 51 Peg has the same mass as the Sun. Mercury's orbital period is 0.24 years, and Venus's is 0.62 years. The average orbital radius of this planet is
less than mercury's
Galileo's contribution to astronomy included
making observations and conducting experiments that dispelled scientific objections to the Sun-centered model
The Moon takes roughly 28 days to complete one orbit around Earth. If the orbital radius of the Moon were twice its actual value, its orbital period would be
more than 56 days
In Ptolemy's Earth-centered model, when would Venus appear directly behind the Sun as viewed from Earth?
never
You discover an asteroid that orbits the Sun with the same 1-year orbital period as Earth. Which of the following statements must be true?
The asteroid's average (semimajor axis) distance from the Sun is 1AU
As a comet orbits around the Sun, its maximum speed is twice its minimum speed. What can we say about its orbit?
The comet is twice as far from the Sun at aphelion as at perihelion
Kepler's First Law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
Kepler's Third Law
The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
All of the following statements are true. Which one can be explained by Kepler's third law?
Venus orbits the Sun at a faster orbital speed than Earth.
When Einstein's theory of gravity (general relativity) gained acceptance, it demonstrated that Newton's theory had been
incomplete
If an astronomer claims to have discovered an object with a very eccentric orbit, which of the following best describes the orbital trajectory of the object?
it looks like a very squashed oval
Why wasn't the Sun-centered model of Copernicus immediately adopted after he proposed it?
it was not noticeably more accurate than the old Ptolemaic model
Kepler's Second Law
As a planet moves around its orbit, it sweeps out equal areas in equal times
Three Key Hallmarks of Science
-Modern science seeks explanations for observed phenomena that rely solely on natural causes -Models must make testable predictions that will force us to revise or abandon the model if they do not agree with observations -Science progresses through the creation and testing of models of nature that explain the observations as simply as possible
Which of the following is not true about a scientific theory?
A theory is essentially an educated guess
Why do the planets orbit the Sun (i.e. why don't they crash into the Sun)?
Although the planets experience a force of gravity from the Sun, since they are moving, their trajectories bend around the Sun rather than lead directly into the Sun
Suppose two comets, comet A and comet B, were orbiting the Sun, having the same average orbital radii. If comet A had a higher eccentricity than comet B, which comet would, during some portion of its orbit, have the highest orbital speed?
Comet A
Two planets are observed going around a star. Planet Xoron has an orbital period that is twice as long as planet Krypton. Which planet has a shorter average orbital radius?
Krypton
All of the following statements are true. Which one can be explained by Kepler's second law?
Mars moves faster in its orbit when it is closer to the Sun than when it is farther from the Sun.
Which of the following is not true about scientific progress?
Science advances only through the scientific method
Earth is slightly closer to the Sun in January than in July. How does the area swept out by Earth's orbit around the Sun during the 31 days of January compare to the area swept out during the 31 days of July?
both of the areas are the same
Tycho Brahe's contribution to astronomy included
collecting data that enabled Kepler to discover the laws of planetary motion.
Consider a planet with an elliptical orbit around the Sun. Its average distance from the Sun is __________
half the distance along a line from the nearest to the farthest points in its orbit
Based on the video, which Venus phase would be impossible to see (from Earth) if Venus orbited Earth as described in Ptolemy's Earth-centered model?
gibbous (nearly full)
If Earth's orbit were very eccentric, but the average distance from the Sun were still 1 AU, its orbital period
would still be one year
