MasteringAstronomy Assignment #8

Discovering Uranus and Neptune (Process of Science)
Part A
Many scientific discoveries are made by chance. While studying one phenomenon, a scientist may discover a different one. Such was the case when William Herschel discovered the planet Uranus in 1781. Herschel was charting faint stars in the sky, when he discovered something that was not a star. How can astronomers tell the difference between a star and a planet?

The following diagram depicts the sky as it would have appeared to Herschel when he first observed Uranus in 1781, as well as the same part of the sky over the next several nights. Label the indicated objects as stars or planets.

Part B
After the discovery of Uranus, astronomers calculated its orbit and predicted its position in the sky using Kepler's laws of planetary motion, which had been known since the early 17th century. However, they soon discovered a small discrepancy between the predicted and actual positions of Uranus. As a scientist, what should you do when presented with such a conflict between prediction and observation?
verify that your observations are correct
think about what else might cause the observed discrepancy
consider that Uranus may not be a planet
consider whether Kepler's laws need to be modified to account for the new observations

Part C
Starting with the hypothesis that a planet near Uranus was the cause of the orbital discrepancy, scientists had to develop a plan to find the unidentified planet. They started with what they knew about the discrepancies in the orbit of Uranus. Rank the steps in the order that scientists would take to discover the planet.

Ranking Task: Planet Temperature, Orbital Period, and Number of Moons
Part A
The following images show five planets in our solar system. Rank these planets from left to right based on their average surface (or cloud-top) temperature, from highest to lowest. (Not to scale.)

Part B
The following images show five planets in our solar system. Rank these planets from left to right based on the amount of time it takes them to orbit the Sun, from longest to shortest. (Not to scale.)

Part C
The following images show four planets in our solar system. Rank these planets from left to right based on the number of moons that orbit them, from highest to lowest. (Not to scale.)

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Why is Saturn's atmosphere almost three times thicker than Jupiter's?
Saturn is less massive than Jupiter; its gravity is weaker.

Which of the following statements is NOT true about Saturn's moon Titan?
Its surface temperature is about the same as that of Earth.

The Roche limit is that distance from a planet where ________.
tidal forces are equal to internal forces

Why did astronomers suspect there was an eighth planet beyond Uranus?
Irregularities in the motion of Uranus suggested that gravity from another planet was affecting it.

All but one of the following properties of Uranus's rings makes them different from the rings of Saturn. Which property is the same for both planets?
They are very thin.

Why is Neptune bluer than Uranus?
It has more methane.

What substance is responsible for the colors of Neptune and Uranus?
Methane

Which of the following statements is NOT true about the magnetic fields of Uranus and Neptune?
They are stronger than the magnetic field of Jupiter.

What evidence suggests that Triton is a captured moon?
It has a retrograde, highly inclined orbit.

Miranda's appearance suggests which of the following statements?
It has been catastrophically disrupted and reassembled several times.

Why are the moons of Uranus and Neptune so dark?
They are subject to radiation darkening.

What is the most significant difference between the Great Dark Spot of Neptune and the Great Red Spot of Jupiter?
The Great Dark Spot has disappeared, whereas the Great Red Spot has been seen for hundreds of years.

As a percentage of their total volumes, how do the cores of Uranus and Neptune compare with those of Saturn and Jupiter?
Their cores are larger than those of Jupiter and Saturn.

What has created Uranus's magnetic field?
A layer of conducting water

In 1781, Uranus was the first new planet to be discovered in how many years?
more than 2000