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Scientists use the light-year to describe the relationships between objects in space. What does a light-year measure?

• the distance that light can travel in one year

• the brightness of light that travels through space

• the number of years it takes light to travel to Earth

• the time it takes light to travel 1 million km

Answer explanation

A light-year measures the distance that light can travel in one year, making it a unit of distance, not time or brightness. This is why the correct answer is 'the distance that light can travel in one year'.

Tags

NGSS.MS-ESS1-3

The average distance between the Sun and Earth is called ...

• a red shift

• The Astronomical Unit

• a light-year

• a parsec

Answer explanation

The average distance between the Sun and Earth is known as The Astronomical Unit (AU). It is a standard measurement in astronomy, while red shift, light-year, and parsec refer to different concepts in space measurement.

Astronomers use the light-year to describe the relationship between objects in space. For example, the Andromeda galaxy is 2.5 million ly from Earth. Which of the following units is most similar to the light-year?

• gram

• second

• kilometer

• degrees Celsius

Answer explanation

The light-year measures distance in space, similar to how kilometers measure distance on Earth. Therefore, the unit most similar to a light-year is the kilometer, as both quantify spatial measurements.

A light-year (ly) is the distance that light travels in one year. If a star is 3 ly from Earth, how long does it take light from that star to reach Earth?

• 3 minutes

• 3 hours

• 3 years

• 3 light-years

Answer explanation

A light-year is the distance light travels in one year. If a star is 3 light-years away, it takes light 3 years to reach Earth. Therefore, the correct answer is 3 years.

Which two objects in space are located farthest apart?

• Earth and Mars

• Earth and the sun

• Earth and the moon

• the Milky Way galaxy and the Andromeda galaxy

Answer explanation

The Milky Way galaxy and the Andromeda galaxy are approximately 2.537 million light-years apart, making them the farthest objects listed. In contrast, Earth, Mars, the sun, and the moon are all much closer to each other.

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NGSS.MS-ESS1-3

Space exploration has advanced our knowledge of the universe. Which space journey would take the longest?

• a journey from Earth to the sun

• a journey from Earth to the moon

• a journey from Earth to a star in the constellation Centaurus

• a journey from Earth to the farthest planet in our solar system, Neptune

Answer explanation

A journey from Earth to a star in the constellation Centaurus would take the longest, as it is located over 4 light-years away, far exceeding the distances to the sun, moon, or Neptune within our solar system.

Tags

NGSS.MS-ESS1-3

Which object is closest to Earth?

• Barnard’s Star

• Planet Neptune

• Andromeda galaxy

• Triangulum galaxy

Answer explanation

Planet Neptune is the closest object to Earth among the options listed. Barnard’s Star is over 5 light-years away, while the Andromeda and Triangulum galaxies are millions of light-years distant.

Which unit is best to measure the distance to Neptune?

• a red shift

• The Astronomical Unit

• a light-year

• a parsec

Answer explanation

The Astronomical Unit (AU) is the average distance from the Earth to the Sun, making it ideal for measuring distances within our solar system, including to Neptune. Other units like light-years and parsecs are better for interstellar distances.

To measure the distance to the Andromeda Galaxy (the nearest full-sized galaxy), astronomers would use ...

• a red shift

• The Astronomical Unit

• a light-year

• a parsec

Answer explanation

To measure the distance to the Andromeda Galaxy, astronomers typically use a light-year, which is the distance light travels in one year. This unit is suitable for astronomical distances, making it the correct choice.

Which stars in the diagram are the coolest?

• white dwarfs

• super giants

• the stars in the upper left corner on the main sequence

• there is no way to know from the diagram