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Chapter 14: Problem 1

Could astronomers in antiquity have seen Uranus? If so, why was it not recognized as a planet?

Short Answer

Expert verified
Yes, Uranus would have been visible to the naked eye under very clear, dark skies. However, it was not recognized as a planet due to its slow apparent motion and the inability of early astronomers to resolve its disk or observe its moons. Without these pieces of evidence, it would have been indistinguishable from a star.

Step by step solution

01

Analyze the Visibility of Uranus

Uranus, being the seventh planet from the Sun, is just about visible to the naked eye under very dark skies. Its apparent magnitude is around +5.7 at opposition, which is within the limit of visibility to the naked eye in areas with low light pollution.
02

Differentiate Between Stars and Planets

Although Uranus might have been seen by ancient astronomers, it would have been recognized as just another star, rather than a planet. This is because planets were distinguished from stars by their movements. Planets move relative to the stars over the course of nights or weeks, hence their name from the Greek 'planetes', which means 'wanderer'.
03

Uranus' Movement and Limitations of Ancient Astronomers

Uranus moves very slowly against the background stars due to its distance from the Earth, taking about 84 years to complete one orbit around the Sun. Its motion would not have been noticeable to the naked eye over a period of a few days or weeks. Additionally, without telescopes, ancient astronomers would not have been able to resolve the disk of Uranus or observe its moons. They also lacked the mathematical tools needed to interpret its motion.

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Most popular questions from this chapter

Compare the rings that surround Jupiter, Saturn, Uranus, and Neptune. Briefly discuss their similarities and differences.

It is thought that Pluto's tenuous atmosphere may become even thinner as the planet moves toward aphelion (which it will reach in 2113), then regain its present density as it again moves toward perihelion. Why should this be?

Briefly describe the evidence supporting the idea that Triton was captured by Neptune.

Why do you suppose the tilt of Uranus's rotation axis was deduced from the orbits of its satellites and not by observing the rotation of the planet itself?

Use the Stary Night Enthusiast \({ }^{\text {TM }}\) program to observe the five large satellites of Uranus. Open the Favourites pane and click on Guides \(>\) Atlas to display the entire celestial sphere. Open the Find pane and double- click the entry for Uranus to center this planet in the view. (Clicking once on the Space bar will speed up this centering). You can reduce the confusion in this view by removing the background stars by clicking on View \(>\) Stars \(>\) Stars and by ensuring that the celestial grid is removed by clicking on View > Celestial Grid. Using the controls at the right-hand end of the toolbar, zoom in to a field of view of about \(2^{\prime} \times 1^{\prime}\). In the toolbar, set the year to 1986 and the Time Flow Rate to 1 hour. Then click on the Run Time Forward button, the right-pointing triangle on the toolbar. You can scroll on and off the labels for the moons by clicking on Labels > Planets-Moons. (a) Describe how the satellites move, and relate your observations to Kepler's third law (see Sections 4-4 and 4-7). (b) Set the year to 2007 and again click on the Run Time Forward button. How do the orbits look different than in (a)? Explain any differences.
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