Astronomy Chapter 13: Uranus and Neptune

Questions and Answers

When and who discovered the planet Uranus?

The planet Uranus was discovered by British astronomer William Herschel in 1781.

Describe the discovery of Uranus.

This was the first new planet discovered in well over 2000 years. The object appeared as a disk in Herschel's 6-inch telescope and moved relative to the stars, indicating it was a planet.

When was the planet Neptune discovered?

A British astronomer, John Adams, reached the solution in September 1846; in June of the following year, French mathematician Urbain Leverrier came up with the same answer.

Describe the discovery of Neptune.

Astronomers charted Uranus' orbit and discovered a discrepancy between the predicted position and the observed position. Signup and view all the answers

How far (in AU) are Uranus and Neptune from the Sun?

Both A and B Signup and view all the answers

How big are Uranus and Neptune in radius compared to Earth?

Both A and B Signup and view all the answers

Why do Uranus and Neptune rotate differentially?

Uranus rotates sideways. Signup and view all the answers

What is the rotation speed of different parts of Uranus?

Uranus's atmosphere rotates faster at the poles (14.2 hours) than near the equator (16.5 hours). Signup and view all the answers

Why is Uranus's rotation classified as retrograde?

Because the north pole lies below the ecliptic plane, the rotation of Uranus is classified as retrograde. Signup and view all the answers

Based on Uranus's axial tilt, why does Uranus have extreme seasons?

At the height of northern summer, the Sun appears to move in a small circle near the north celestial pole, causing extreme seasonal variations. Signup and view all the answers

Why on Uranus during the spring and autumn equinox is the day and night each 8.5 hours long; and during the summer and winter, they are each about 20 years long?

Due to the axial tilt, as Uranus moves along its orbit, the length of day and night changes dramatically, with extremes reaching 20 years. Signup and view all the answers

What are the average rotation speeds of Neptune's atmosphere and its interior?

Neptune's atmosphere rotates once every 17.3 hours, while its interior rotates once every 16.1 hours. Signup and view all the answers

Based on rotation, how is Neptune unique among the jovian planets?

Neptune's atmosphere rotates more slowly than its interior. Signup and view all the answers

What are Uranus and Neptune composed of?

They are composed primarily of hydrogen (84%), followed by helium (14%) and methane. Signup and view all the answers

What are the dominant gases in the atmospheres of both planets?

The most abundant element is hydrogen. Signup and view all the answers

Explain how the amount of ammonia and methane varies among the jovian planets moving outward from the Sun.

The more distant planets have steadily decreasing amounts of ammonia and greater amounts of methane. Signup and view all the answers

Why are Uranus bluish-green and Neptune blue in color?

The increasing amounts of methane absorb red light, giving both planets their characteristic colors. Signup and view all the answers

Study Notes

Discovery of Uranus and Neptune

Uranus was discovered by British astronomer William Herschel in 1781, making it the first planet found telescopically.
Herschel observed Uranus as a disk in his 6-inch telescope, noting its slow movement, which distinguished it from a comet.
Neptune was discovered through calculations by British astronomer John Adams in September 1846 and confirmed by French mathematician Urbain Leverrier in June 1847.

Orbital Characteristics and Distance

Uranus is located approximately 19 AU from the Sun, while Neptune is around 30 AU away.
Uranus has a radius about 14.5 times that of Earth, and Neptune's radius is approximately 17 times greater.
Uranus has an axial tilt of 98 degrees, resulting in its unique sideways rotation, whereas Neptune has a tilt of 30 degrees.

Rotation and Seasons

Uranus experiences differential rotation, with a faster rotation period at the poles (14.2 hours) compared to the equator (16.5 hours).
Uranus's rotation is classified as retrograde due to its north pole being below the ecliptic plane.
Extreme seasons on Uranus cause the sun to circle the sky during northern summer, leading to day lengths of up to 20 Earth years during winter.

Neptune's Unique Rotation

Neptune's atmosphere rotates with a period of 17.3 hours, while its interior rotates once every 16.1 hours, making it unique among jovian planets.
This slower atmospheric rotation compared to the interior is distinct for Jupiter and Saturn.

Atmospheric Composition

Both Uranus and Neptune are primarily composed of hydrogen (84%), helium (about 14%), and methane (2% on Uranus and 3% on Neptune).
The dominant gases in their atmospheres are primarily hydrogen, with methane affecting their colors.

Coloration and Chemical Variations

The blue hues of Uranus and Neptune are due to increasing amounts of methane, which absorbs longer wavelengths of red light.
As the distance from the Sun increases, the amount of ammonia decreases and methane becomes more prevalent, contributing to the characteristic blue coloration of these outer planets.

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Explore the fascinating discoveries of Uranus and Neptune with this quiz. Learn about the history and significance of these distant planets, including the role of William Herschel in discovering Uranus. Test your knowledge of key facts and definitions related to these celestial bodies.