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Chapter 2: Problem 8

We always see the same side of the Moon because a. the Moon does not rotate on its axis. b. the Moon rotates on its axis once for each revolution around Earth c. when the other side of the Moon is facing Earth, it is unlit. d. when the other side of the Moon is facing Earth, it is on the opposite side of Earth.

Short Answer

Expert verified
b. the Moon rotates on its axis once for each revolution around Earth

Step by step solution

01

Understand the Question

The problem is asking why we always see the same side of the Moon from Earth.
02

Analyze Option A

Option A states that the Moon does not rotate on its axis. This is incorrect because the Moon does indeed rotate on its axis.
03

Analyze Option B

Option B states that the Moon rotates on its axis once for each revolution around Earth. If the Moon did this, the same side would always face Earth.
04

Analyze Option C

Option C claims that when the other side of the Moon faces Earth, it is unlit. This is not a reason for why we always see the same side from Earth; it describes a different phenomenon.
05

Analyze Option D

Option D claims that when the other side of the Moon faces Earth, it is on the opposite side of Earth. This is not correct because the Moon does not go behind Earth completely in its orbit.
06

Determine the Correct Answer

Since Option B correctly explains the synchronous rotation of the Moon, it must be the correct answer.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lunar rotation
Lunar rotation refers to the Moon spinning around its own axis. Many people mistakenly think the Moon doesn't rotate, but that's not true. The Moon does rotate, but it does so in a special way. It completes one full spin on its axis in the same time it takes to orbit Earth. This means it takes about 27.3 days for one rotation and one orbit. Because these times are the same, we always see the same side of the Moon from Earth. This synchronized spinning and orbiting is called synchronous rotation. Understanding this is key to explaining why we only ever get one view of the Moon from our planet.
Earth-Moon system
The Earth-Moon system describes the gravitational and orbital relationship between our planet and its only natural satellite, the Moon. This system is unique and vital for several reasons:
  • The Moon's gravity affects Earth's tides.
  • The Earth provides the gravitational pull that keeps the Moon in orbit.
In this relationship, Earth and the Moon are locked in a dance due to mutual gravitational pull. The Moon's synchronous orbit is one outcome of this balance. Due to Earth's stronger gravity, the Moon's rotation has gradually slowed down over millions of years, leading to its current synchronous rotation. Therefore, understanding the Earth-Moon system is crucial for realizing why the Moon behaves the way it does.
Synchronous orbit
A synchronous orbit happens when an astronomical body's orbital period matches its rotational period. For the Moon, this means it takes the same amount of time to circle Earth as it does to spin once around its axis. This is why we always see the same side of the Moon—this side is always facing Earth. The Moon's synchronous orbit results from tidal locking, a natural process caused by the gravitational forces between Earth and the Moon over a long time. This orbit creates a stable and consistent view for observers on Earth. Understanding synchronous orbits can help explain similar phenomena observed in other planets and moons in our solar system and beyond.

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Most popular questions from this chapter

Go to the "Earth and Moon Viewer" website (http://fourmilab. ch/earthview). Under "Viewing the Earth," click on "latitude, longitude and altitude" and enter your approximate latitude and longitude, and 40,000 for altitude; then select "View Earth." Are you in daytime or nighttime? Now play with the locations; keep the same latitude but change to the opposite hemisphere (Northern or Southern). Is it still night or day? Go back to your latitude, and this time enter \(180^{\circ}\) minus your longitude, and change from west to east, or from east to west, so that you are looking at the opposite side of Earth. Is it night or day there? What do you see at the North Pole (latitude \(90^{\circ}\) north) and the South Pole (latitude \(90^{\circ}\) south)? At the bottom of your screen you can play with the time. Move back 12 hours. What do you observe at your location and at the poles?

Imagine that you are standing on the South Pole at the time of the southern summer solstice. a. How far above the horizon will the Sun be at noon? b. How far above (or below) the horizon will the Sun be at midnight?

The Sun, Moon, and stars a. appear to move each day because the celestial sphere rotates about Earth. b. change their relative positions over time. c. rise north or south of west and set north or south of east, depending on their location on the celestial sphere. d. always remain in the same position relative to each other.

Polaris was used for navigation by seafarers such as Columbus as they sailed from Europe to North America. When Magellan sailed the South Seas, he could not use Polaris for navigation. Explain why.

Suppose you would like to witness the midnight Sun (when the Sun appears just above the northern horizon at midnight) but you don't want to travel any farther north than necessary. a. How far north (that is, to which latitude) would you have to go? b. At what time of year would you make this trip?
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