Astronomy Quiz

Cepheid variable stars are critical for measuring cosmic distances because:

• Their period is inversely proportional to their brightness.

• The period of variation is proportional to their luminosity.

• They have identical brightness regardless of location.

• Their distance is determined through parallax.

Answer explanation

Cepheid variable stars have a well-defined relationship where their period of variation is directly proportional to their luminosity. This allows astronomers to determine distances based on their observed brightness.

If a Cepheid star in a spiral nebula is 100 times dimmer than a local Cepheid star, the spiral nebula is approximately:

• 2 times farther.

• 10 times farther.

• 100 times farther.

• 1,000 times farther.

Answer explanation

The brightness of a star decreases with the square of the distance. If a Cepheid star is 100 times dimmer, it is 100 times farther away, as brightness is inversely proportional to the square of the distance.

If the orbital distance of a planet doubles, how does the orbital period change?

• It doubles.

• It increases by a factor of 2√2.

• It increases by a factor of 22√2.

• It increases by a factor of 888.

Answer explanation

According to Kepler's Third Law, the square of the orbital period (T) is proportional to the cube of the semi-major axis (a). If the distance doubles (a becomes 2a), T increases by a factor of (2^3)^(1/2) = 2√2, making the correct answer 22√2.

Tags

NGSS.HS-ESS1-4

NGSS.HS-PS2-4

Which of the following correctly describes elliptical galaxies?

• Disk-like, blue, and luminous.

• Elliptical shape, dusty, and luminous.

• Elliptical shape, redder, and lacking star formation.

• Irregular shape, chaotic, and star-forming.

Answer explanation

Elliptical galaxies are characterized by their elliptical shape, a redder color due to older stars, and a lack of significant star formation, distinguishing them from other galaxy types.

Why do massive blue stars have shorter lifetimes compared to smaller stars?

• They burn through their fuel much faster despite having more fuel.

• They lack hydrogen fusion, leading to faster collapse.

• Their luminosity decreases rapidly over time.

• Gravity pulls them inward too quickly for stable fusion.

Answer explanation

Massive blue stars have higher temperatures and pressures in their cores, leading to rapid fusion of hydrogen into helium. This accelerated fuel consumption results in shorter lifetimes, despite having more fuel available.

Tags

NGSS.HS-ESS1-1

The spiral structure of galaxies is primarily explained by:

• Gravitational collapse with angular momentum conservation.

• Star formation occurring in specific elliptical regions.

• Black hole dynamics in galaxy cores.

• Irregular interactions with dark matter.

Answer explanation

The spiral structure of galaxies is primarily due to gravitational collapse, where matter clumps together under gravity while conserving angular momentum, leading to the formation of spiral arms.

Tags

NGSS.HS-PS2-4

Which observation provides direct evidence for the existence of dark matter?

• Gravitational lensing of distant galaxies.

• The brightness of Cepheid variable stars.

• Absorption spectra from nebulae.

• Angular momentum of collapsing gas clouds.

Answer explanation

Gravitational lensing of distant galaxies occurs when massive objects bend light, providing direct evidence of dark matter's presence, as it indicates unseen mass influencing light paths.

What is the surprising result of measuring orbital velocities at increasing distances from galaxy centers?

• Velocities decrease significantly as predicted by Newtonian dynamics.

• Velocities remain constant, suggesting unseen mass.

• Velocities fluctuate irregularly due to chaotic star motions.

• Velocities depend solely on visible luminous matter.

Answer explanation

The surprising result is that orbital velocities remain constant at increasing distances from galaxy centers, contrary to Newtonian predictions. This suggests the presence of unseen mass, such as dark matter, influencing the galaxy's dynamics.

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-4

Elliptical galaxies contain fewer blue stars because:

• Blue stars burn out quickly, and no new stars are forming.

• Elliptical galaxies lack the dust needed for blue star formation.

• Mergers destroy blue stars.

• Blue stars are hidden by dark matter.

Answer explanation

Blue stars burn out quickly, typically within a few million years, and elliptical galaxies have exhausted their gas supply, leading to no new star formation. This results in fewer blue stars compared to other galaxy types.

Tags

NGSS.HS-ESS1-3

Why is the parallax method ineffective for measuring very distant galaxies?

• Distant galaxies do not move relative to background stars.

• Parallax angles become too small to detect.

• Light from distant galaxies cannot penetrate the interstellar medium.

• Cepheid variable stars are too faint at those distances.

Answer explanation

The parallax method relies on measuring small angles. For very distant galaxies, these angles become exceedingly small, making them difficult to detect accurately, which is why this method is ineffective at such distances.