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Chapter 1: Problem 17

A light-year is a measure of a. distance. b. time. c. speed. d. mass.

Short Answer

Expert verified
a. distance.

Step by step solution

01

Determine the Definition of a Light-Year

A light-year is defined as the distance that light travels in a vacuum in one year.
02

Analyze the Units Involved

Since a light-year measures the distance light travels over a period of one year, it involves units of distance rather than time, speed, or mass.
03

Identify the Correct Answer

By understanding the definition and the units involved, determine that the correct answer related to distance.

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Key Concepts

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

Distance Measurement
A light-year is a unit used to measure extremely large distances, typically in space. It represents the distance that light travels in one year. To grasp this better, think about the vastness of the universe and how regular units like kilometers or miles are not practical for such large distances. Instead, astronomers use the light-year.

For example, the nearest star to Earth, Proxima Centauri, is about 4.24 light-years away. This means the light we see from that star took 4.24 years to reach us.

Understanding the scale of a light-year helps us measure and comprehend the enormous distances between celestial objects efficiently.
Light Travel
Light travels incredibly fast. In a vacuum, it moves at roughly 299,792 kilometers per second (km/s). When we say that something is 'light-years' away, we're combining this speed with the concept of time.

To put this into perspective, light from the Sun takes about 8 minutes and 20 seconds to reach Earth. So, when we observe the Sun, we are actually seeing it as it was 8 minutes ago.

This rapid speed is what makes light a reliable measurement tool for vast cosmic distances. By comprehending light's travel time, we can better appreciate and quantify the universe's vast expanse.
Astronomical Units
An astronomical unit (AU) is another distance measurement used in astronomy. One AU corresponds to the average distance between the Earth and the Sun, approximately 149.6 million kilometers.

Astronomers use AUs to simplify the relative distances within our solar system. For example, Jupiter is about 5.2 AUs from the Sun. While the light-year is ideal for interstellar distances, the AU is convenient for shorter, solar system-scale measurements.

Both units index the enormous scales we deal with in astronomy, making it easier to convey information about how far objects are from Earth.
Vacuum Travel
Light travels fastest in a vacuum, where there are no particles to slow it down. In space, which is a near-perfect vacuum, light can maintain its maximum speed of 299,792 km/s.

This constant and unimpeded speed is essential for accurately measuring distances. If light were to travel through a medium like water or air, its speed would decrease due to interactions with particles.

Thus, when we discuss a light-year, it is critical to note that this measurement is based on light traveling in a vacuum, ensuring consistent and precise distance calculations.

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Most popular questions from this chapter

Rank the following in order of increasing size. a. Local Group b. Milky Way c. Solar System d. universe e. Sun f. Earth g. Virgo Supercluster

Suppose you set your keys on the table and left the room. When you came back, they were on the ground. Which of the following is most likely to be true, given the application of Occam's razor? a. Invisible flying elephants carried them to the floor b. They just walked off by themselves. c. Someone bumped the table and knocked them off. d. A violent wind blew them off the table.

Go to the Astronomy Picture of the Day (APOD) app or website (http://apod.nasa.gov/apod) and click on "Archive" to look at the recent pictures and videos. Submissions to this website come from all around the world. Pick one and read the explanation. Was the image or video taken from Earth or from space? Is it a combination of several images? Does it show Earth, our Solar System, objects in our Milky Way Galaxy, more distant galaxies, or something else? Is the explanation understandable to someone who has not studied astronomy? Do you think this website promotes a general interest in astronomy?

If a car is traveling at \(35 \mathrm{km} / \mathrm{h}\), how far does it travel in a. one hour? b. half an hour? c. one minute?

(a) If it takes about 8 minutes for light to travel from the Sun to Earth, and Pluto is 40 times farther from Earth than the Sun is, how long does it take light to reach Earth from Pluto? (b) Radio waves travel at the speed of light. What does this fact imply about the problems you would have if you tried to conduct a two-way conversation between Earth and a spacecraft orbiting Pluto?
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