CHAPTER 25 Study Guide
25.1 Exploring the Solar System
Key Concepts
In a geocentric model, Earth is stationary while objects in the sky move around it.
In a heliocentric model, Earth and the other planets revolve around the sun.
Gravity and inertia combine to keep the planets in orbit around the sun.
Our solar system consists of the sun, the planets, their moons, and a variety of smaller objects that revolve around the sun.
Modern technology, including complex telescopes, piloted spacecraft, and space probes, has allowed scientists to explore the solar system.
Vocabulary
geocentric, p. 791; heliocentric, p. 791; ecliptic plane, p. 792; moon, p. 792; astronomical unit, p. 793; space probe, p. 794
25.2 The Earth-Moon System
Key Concepts
The lack of an atmosphere allows the moon's surface temperature to vary tremendously.
The major surface features of the moon are maria, highlands, and craters.
Scientists hypothesize that the moon formed after an enormous collision early in Earth's history.
The moon's phases are caused by changes in the relative positions of the moon, sun, and Earth as the moon revolves around Earth.
A solar eclipse occurs when the moon casts a shadow on a portion of Earth's surface.
A lunar eclipse occurs when Earth casts a shadow on the moon.
Tides are caused mainly by differences in the moon's gravitational pull on Earth.
Vocabulary
maria, p. 797; crater, p. 797; meteoroids, p. 797; phases, p. 798; eclipse, p. 799; umbra, p. 800; penumbra, p. 800; tides, p. 801; spring tide, p. 801; neap tide, p. 801
25.3 The Inner Solar System
Key Concepts
The four inner planets are all relatively small and dense, and have rocky surfaces.
Scientists now hypothesize that asteroids are remnants of the early solar system.
Vocabulary
terrestrial planets, p. 803; asteroids, p. 809; asteroid belt, p. 809
25.4 The Outer Solar System
Key Concepts
The four gas giants are thought to have small, dense cores, and thick atmospheres that are mostly hydrogen and helium.
A dwarf planet is spherical and orbits the sun, but has not cleared the neighborhood around its orbit.
Comets are dusty pieces of ice and rock. Meteoroids are pieces of rock moving through space.
The Kuiper belt is a doughnut-shaped region near the ecliptic. The Oort cloud is a reservoir of comets.
Vocabulary
gas giants, p. 811; ring, p. 811; Kuiper belt, p. 815; Oort cloud, p. 815
25.5 The Origin of the Solar System
Key Concepts
The nebular theory states that the solar system formed from a rotating cloud of dust and gas.
The terrestrial planets are small and rocky because the inner solar system was too hot during their formation for ice-forming compounds to condense. The gas giants are large and have low densities because the outer solar system was much cooler.
Vocabulary
solar nebula, p. 818; protoplanetary disk, p. 819; planetesimals, p. 819; accretion, p. 819
Thinking Visually
Compare-and-Contrast Table Make a table comparing and contrasting the terrestrial planets, gas giants, and Pluto.
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