Unit 2 Lesson 2 "Earth and the Solar System"

Dwarf planets are smaller than planets. What is another way that dwarf planets are different?

• They are not spherical.

• They do not orbit the sun.

• They have large objects in their orbit.

• They move more slowly along their orbits.

As astronomers observe an object in space that has an irregular shape, that orbits the sun in a highly elliptical orbit, and that is made of ice and rock. Which object is the astronomer most likely observing?

• moon

• comet

• asteroid

• meteoroid

An astronomer uses parallax to determine a star’s distance from Earth. Which statement correctly describes parallax?

• A. Stars closer to Earth will have a dimmer appearance.

• B. Stars farther away from Earth will have a dimmer appearance.

• C. Stars closer to Earth will appear to have a greater shift in position.

• D. Stars farther away from Earth will appear to have a greater shift in position.

Which statement describes a limitation of the model?

• A. It cannot show how the planets orbit the sun.

• B. It cannot show the relative sizes of each planet.

• C. It does not show the gravitational force exerted by each planet.

• D. It does not show the order of the planets, from closest to the sun to farthest from the sun.

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Early astronomers noticed that some stars in the sky appeared to move together across the sky as constellations. How do astronomers today explain this motion?

• The sun’s gravity keeps the stars together because they orbit the sun at the same rate.

• The stars appear to move together along a path because of Earth’s rotation on its axis.

• Gravitational attraction between the stars keeps them fixed relative to each other as they move.

• The stars move around Earth in the same way, so their positions relative to each other stay the same.

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Match the event to the order they happened.

• First

• Scientists observe planetary motion that cannot be explained if Earth is the center of the universe

• Third

• Scientists accept the theory that the planets and sun travel around Earth

• Second

• Scientists develop the theory that the planets travel around the sun.

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The dotted lines in the picture show orbital paths of objects. Which object orbits object E?

• object A

• object B

• object C

• object D

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Retrograde motion refers to the apparent backward movement of planets in the sky, which confused early astronomers because it did not fit with the idea that all celestial objects move in perfect circles around the Earth. Which of the following best explains why retrograde motion was confusing to early astronomers?

• It appeared as if planets reversed direction, which did not match the geocentric model.

• It showed that planets always moved in straight lines.

• It proved that the Sun revolved around the Earth.

• It indicated that stars could change their brightness suddenly.

Ptolemy’s concept of epicycles improved on Aristotle’s model of how objects move in the solar system by:

• Explaining retrograde motion by stating that the planets moved in small circles as they orbit the Earth.

• eliminating the need for circular orbits

• proposing that planets move in straight lines

• suggesting that the Sun is at the center of the universe

Copernicus’s heliocentric model of the solar system states that:

• the Sun is at the center of the solar system

• the Earth is at the center of the solar system

• the Moon is at the center of the solar system

• all planets revolve around the Earth

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