Chapters 14–16: Stars, Solar System, and Earth–Moon–Sun System

Flashcards covering key questions and answers from Chapters 14–16 on stars, the solar system, and Earth–Moon–Sun interactions.

What is a light-year?

The distance light travels in one year, about 9.46 trillion kilometers.

Why do astronomers use light-years instead of kilometers or miles?

Because astronomical distances are so large that conventional units would create impractically huge numbers.

What are the three main internal layers of a star?

Core, Radiation Zone, and Convection Zone.

In which part of a star does nuclear fusion occur?

The core.

Which type of star has the longest lifespan?

Low-mass stars.

What property determines a star’s position on the main sequence?

Its mass.

What is the difference between apparent magnitude and absolute magnitude?

Apparent magnitude is a star’s brightness as seen from Earth; absolute magnitude is its intrinsic brightness if all stars were the same distance away.

How does a star’s color relate to its surface temperature?

Blue stars are hotter, while red stars are cooler.

What is the life cycle of an average-mass star?

Protostar → Main Sequence → Red Giant → White Dwarf → Carbon lump.

Where are elements heavier than iron created?

In supernova explosions.

What are two key uncertainties in the protoplanet nebular model?

Why planets formed where they did, and why inner planets are rocky while outer planets are gaseous (also why the original disk did not remain).

What are terrestrial planets?

Rocky planets with metallic cores: Mercury, Venus, Earth, and Mars.

What are giant planets primarily made of?

Hydrogen, helium, and methane, surrounding rocky cores.

Which planets in our solar system have rings?

Jupiter, Saturn, Uranus, and Neptune.

What is unusual about the rotations of Venus and Uranus?

Venus rotates opposite most planets (retrograde), and Uranus is tilted on its side with an extreme axial tilt.

What are asteroids?

Rocky or iron bodies that orbit the Sun mainly between Mars and Jupiter.

Where do most comets originate?

The distant outer regions of the solar system.

What is a meteor?

A streak of light produced when a space particle burns in Earth’s atmosphere.

What is a meteorite?

A fragment of rock or metal from space that survives passage through the atmosphere and lands on Earth’s surface.

What is the formula for converting Celsius to Fahrenheit?

T°F = (9/5) × T°C + 32.

Which motion of Earth is independent of the Sun?

Earth’s rotation on its axis.

What are two pieces of evidence that Earth is spherical?

Curved shadow on the Moon during an eclipse and objects gradually disappearing below the horizon as they move away.

What experiment demonstrates that Earth rotates?

The Foucault pendulum.

What causes the yearly change in daylight hours?

The constant tilt of Earth’s axis relative to its orbital plane.

What causes Earth’s seasons?

The constant tilt of Earth’s axis relative to the ecliptic as Earth orbits the Sun.

What does the word “solstice” mean?

“Sun stand still,” referring to the Sun’s apparent halt in its north–south drift.

What does the word “equinox” mean?

“Equal nights,” indicating roughly equal day and night lengths.

What is precession?

The slow wobble of Earth’s rotational axis over ~26,000 years.

What is the northernmost latitude where the Sun can be directly overhead?

The Tropic of Cancer (about 23.5° N).

Why doesn’t a lunar eclipse occur every month?

Because the Moon’s orbital plane is tilted relative to Earth’s orbital plane, so the Sun, Earth, and Moon don’t align each month.

What is a total solar eclipse?

When the Moon’s umbra (full shadow) completely covers a portion of Earth, blocking the Sun entirely.

What created most of the Moon’s craters?

Impacts from meteoroids, asteroids, and other rock fragments.

What is an annular solar eclipse?

An eclipse in which the Sun appears as a bright ring around the Moon because the Moon is too far away to cover the Sun completely.

What was the primary problem with the Julian calendar?

Its year was about 11 minutes 14 seconds too long, causing gradual drift of dates relative to seasons.

How did the Moon form, according to the giant-impact hypothesis?

From debris ejected when a Mars-sized object collided with the early Earth.