SC.8.E.5.2 Universe and Galaxies

Which of the following best describes a galaxy?

• A large collection of stars, dust, and gas bound together by gravity.

• A single star with its planetary system.

• A small cluster of planets orbiting a star.

• A group of asteroids and comets.

Answer explanation

A galaxy is defined as a large collection of stars, dust, and gas bound together by gravity, making the first choice the correct description. The other options refer to smaller astronomical structures.

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How does the number of stars in a galaxy compare to the number of galaxies in the universe?

• There are more galaxies than stars in a galaxy.

• There are more stars in a galaxy than galaxies in the universe.

• The number of stars in a galaxy is roughly equal to the number of galaxies in the universe.

• There are more galaxies in the universe than stars in a galaxy.

Answer explanation

A typical galaxy contains billions to trillions of stars, while the observable universe has around 2 trillion galaxies. Therefore, there are more stars in a galaxy than galaxies in the universe.

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If you were to plan a mission to study a distant galaxy, which of the following factors would be most important to consider?

• The distance to the galaxy and the technology available for travel.

• The number of planets in our solar system.

• The color of the stars in the galaxy.

• The number of moons orbiting Earth.

Answer explanation

The most important factors for a mission to study a distant galaxy are the distance to the galaxy and the technology available for travel, as they directly impact feasibility and mission planning.

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Which statement best explains why galaxies do not collide frequently despite their large numbers?

• Galaxies are stationary and do not move.

• The vast distances between galaxies make collisions rare.

• Galaxies repel each other due to magnetic forces.

• Galaxies are protected by a cosmic shield.

Answer explanation

The vast distances between galaxies make collisions rare. Despite their large numbers, the space separating them is immense, which significantly reduces the likelihood of any two galaxies colliding.

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Which of the following is a characteristic of most galaxies?

• They contain only one star.

• They are composed of billions of stars.

• They are smaller than solar systems.

• They are made entirely of gas.

Answer explanation

Most galaxies are composed of billions of stars, making them vast collections of stellar bodies. The other options are incorrect as galaxies contain many stars, are larger than solar systems, and are not made entirely of gas.

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What is the primary reason that galaxies are classified into different types?

• To determine the age of the universe.

• To understand the structure and formation of the universe.

• To count the number of stars in each galaxy.

• To measure the distance between galaxies.

Answer explanation

Galaxies are classified to understand their structure and formation, which helps astronomers learn about the evolution of the universe. This classification reveals insights into the processes that shape galaxies over time.

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Which strategy would be most effective in identifying the type of galaxy you are observing?

• Count the number of stars visible in the galaxy.

• Analyze the shape and structure of the galaxy.

• Measure the temperature of the galaxy's core.

• Determine the number of planets orbiting its stars.

Answer explanation

Analyzing the shape and structure of a galaxy is crucial for classification, as it reveals whether the galaxy is spiral, elliptical, or irregular, which are key identifiers. Other options do not provide definitive classification.

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What concept explains why galaxies appear to be moving away from each other?

• The gravitational pull of black holes.

• The expansion of the universe.

• The rotation of the Milky Way.

• The collision of galaxies.

Answer explanation

The expansion of the universe explains why galaxies appear to be moving away from each other. This phenomenon, observed as redshift, indicates that space itself is stretching, causing galaxies to recede over time.

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Everything that exists, including all matter and energy. Mostly consists of empty space.

• a galaxy

• a black hole

• the universe

• the multiverse

Answer explanation

The universe encompasses everything that exists, including all matter and energy, and is primarily composed of empty space. This makes 'the universe' the correct choice, as it includes all galaxies, black holes, and more.

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Gas, dust, billions of stars and planets describes what space entity?

• Solar System

• Galaxy

• Moon

• Sun

Answer explanation

A galaxy is a vast collection of gas, dust, billions of stars, and planets, all bound together by gravity. In contrast, the solar system is just one part of a galaxy, while the moon and sun are specific celestial bodies.