Stars & the Universe — Chapter quiz · Earth & Space Science, Grade 9

Use stellar models, diagrams, and spectra to explain energy, elements, and cosmic history.

Problem 1

Which explains a massive main-sequence star’s short lifetime?
  1. It contains no hydrogen.
  2. Its fuel-use rate is very high.
  3. It receives no gravity.
  4. Its light cannot leave.
Answer and explanation

Its fuel-use rate is very high.

High output can exhaust usable fuel faster despite a larger supply.

Problem 2

Describe the chain connecting fusion in the Sun to warming at Earth’s surface.
Answer and explanation

Fusion releases energy, energy moves through the solar interior, radiation leaves the surface and crosses space, and absorption transfers energy to Earth.

Problem 3

Independent chapter check: Model star B has four times A’s available fuel but eighty times its fuel-use rate. Estimate its lifetime relative to A and explain why this is a ratio model rather than a complete stellar-evolution forecast.
Answer and explanation

The ratio is 4/80 = 0.05, so B’s lifetime scale is one twentieth of A’s. Actual evolution also depends on initial mass, composition, core structure and changing conditions; these supplied ratios are not a universal stellar formula.

The ratio is 4/80 = 0.05, so B’s lifetime scale is one twentieth of A’s. Actual evolution also depends on initial mass, composition, core structure and changing conditions; these supplied ratios are not a universal stellar formula.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

Two stars have equal luminosity with no intervening absorption. The farther one appears…
  1. brighter
  2. fainter
  3. necessarily hotter
  4. necessarily larger
Answer and explanation

fainter

Its radiation spreads over a larger area before reaching the observer.

Problem 5

A star is plotted cool and luminous. Explain why “cool means low luminosity” is not generally valid.
Answer and explanation

Total output depends on emitting area as well as surface temperature; a cool large giant can be luminous.

Problem 6

Independent chapter check: Two ideal stars have equal surface temperature; star B has radius twice A’s. Find B/A luminosity. At the same observer distance and unobscured path, compare received brightness. Name one condition that would break the simple comparison.
Answer and explanation

Luminosity factor is 2² = 4 and received brightness is also four at equal distance/path conditions. Different temperatures, extinction or emission/measurement conditions would require additional factors.

Luminosity factor is 2² = 4 and received brightness is also four at equal distance/path conditions. Different temperatures, extinction or emission/measurement conditions would require additional factors.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 7

A 500 nm line is observed at 600 nm. Find z.
Answer and explanation

0.2

100 ÷ 500 = 0.20.

Problem 8

Why is one nearby galaxy moving toward us not enough to refute cosmic expansion?
Answer and explanation

Local gravitational motions can differ from the large-scale expansion pattern; evaluate many distant galaxies and independent evidence.

Problem 9

Independent chapter check: A 500 nm laboratory line is observed at 575 nm, and a 600 nm line at 690 nm. Calculate z for each. Explain what the agreement supports and what it does not uniquely establish.
Answer and explanation

Both give z = 0.15: 75/500 and 90/600. Agreement supports a common fractional shift of that identified pattern, while the physical cause, distance and full cosmological interpretation need context, calibration and additional evidence.

Compute (575−500)/500 = 0.15.

Compute (690−600)/600 = 0.15.

Interpret the common fractional shift without assigning a unique cause from arithmetic alone.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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