Astronomy Practice Tests
Free, AI-generated Astronomy practice tests for Science Olympiad. Choose Invitational, Regional, State, or National difficulty, import past exam PDFs, and track your scores over time.
Astronomy runs in Division C for the 2027 season.
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Astronomy Sample Practice Questions
1. Two stars have the same luminosity. If Star B is twice as far away as Star A, how does its apparent brightness compare?
- Half as bright
- One-quarter as bright
- Twice as bright
- Four times as bright
Show answer and explanation
Answer: One-quarter as bright
Apparent brightness follows the inverse-square law. Doubling the distance reduces the received flux to 1/2², or one-quarter.
2. What is the spectral type and luminosity class of the Sun?
- O5V
- G2V
- M0III
- B8V
Show answer and explanation
Answer: G2V
The Sun is a G2 (yellow, ~5,800 K surface) main-sequence dwarf - "V" is the luminosity class for main-sequence stars.
3. A star has a parallax of 0.05 arcseconds. Its distance is:
- 5 parsecs
- 20 parsecs
- 50 parsecs
- 200 parsecs
Show answer and explanation
Answer: 20 parsecs
Stellar parallax follows d(pc) = 1/p(arcsec): 1 ÷ 0.05 = 20 pc (about 65 light-years).
4. A star has apparent magnitude m = 8 and absolute magnitude M = 3. Its distance is:
- 10 parsecs
- 100 parsecs
- 1,000 parsecs
- 10,000 parsecs
Show answer and explanation
Answer: 100 parsecs
The distance modulus m - M = 5 log(d/10) gives 8 - 3 = 5, so log(d/10) = 1 and d = 100 pc.
5. Which of these stars will END its life as a white dwarf?
- A 2 M☉ star
- A 10 M☉ star
- A 25 M☉ star
- A 60 M☉ star
Show answer and explanation
Answer: A 2 M☉ star
Only stars below roughly 8 M☉ shed their envelopes as planetary nebulae and leave white dwarfs. The 10 M☉ star ends as a neutron star; the 25 and 60 M☉ stars collapse into black holes.
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Indexed Astronomy Practice Tests by Difficulty
Reviewed full-length Astronomy practice tests, each with every question and answer choice listed on its own page.
What Astronomy Tests Cover
stellar evolution, HR diagrams, galaxy types, planetary science, celestial mechanics, cosmology, and observational techniques.
Key formulas (verify all calculations)
- Distance modulus: m - M = 5 log(d/10), where d is in parsecs, m = apparent magnitude, M = absolute magnitude
- Parallax: d(pc) = 1/p(arcsec). Example: p = 0.1 arcsec → d = 10 pc
- Stefan-Boltzmann Law: L = 4πR²σT⁴ (σ = 5.67×10⁻⁸ W/m²K⁴). Luminosity ∝ R²T⁴
- Wien's Law: λmax = 2.898×10⁻³/T (meters). Hotter = shorter wavelength (bluer)
- Kepler's 3rd Law: P² = a³ (P in years, a in AU) OR P² = (4π²/GM)a³
- Escape velocity: v = √(2GM/r)
- Orbital velocity: v = √(GM/r)
- Schwarzschild radius: Rs = 2GM/c²
- Hubble's Law: v = H₀d (H₀ ≈ 70 km/s/Mpc)
- Apparent brightness: b = L/(4πd²)
Stellar classification
- Spectral types (hot→cool): O B A F G K M ("Oh Be A Fine Girl/Guy Kiss Me")
- O: >30,000K, blue, ionized helium lines
- B: 10,000-30,000K, blue-white, neutral helium
- A: 7,500-10,000K, white, strong hydrogen lines (Vega, Sirius)
- F: 6,000-7,500K, yellow-white
- G: 5,200-6,000K, yellow (Sun = G2V)
- K: 3,700-5,200K, orange
- M: <3,700K, red, molecular bands (TiO)
- Luminosity classes: I (supergiant), II (bright giant), III (giant), IV (subgiant), V (main sequence/dwarf)
Hr diagram
- X-axis: Temperature (DECREASING left to right) or Spectral type (O→M) or Color index (B-V)
- Y-axis: Luminosity (increasing up) or Absolute magnitude (decreasing up, brighter = more negative)
- Main sequence: Diagonal band, hydrogen fusion, ~90% of stars
- Red giants: Upper right, hydrogen shell burning, expanded cool stars
- White dwarfs: Lower left, hot but dim, Earth-sized, electron degeneracy
- Mass determines position on main sequence: More massive = hotter, brighter, shorter-lived
Stellar evolution
- Low mass (<0.5 M☉): Main-sequence lifetime exceeds the age of the universe, so none have evolved off it yet. The lowest-mass stars (≲0.25 M☉) are predicted to skip the red giant phase and fade into helium white dwarfs.
- Medium mass (0.5-8 M☉): Main sequence → Red giant → Helium flash → Horizontal branch → AGB → Planetary nebula → White dwarf
- High mass (>8 M☉): Main sequence → Supergiant → Supernova → Neutron star (1.4-3 M☉) or Black hole (>3 M☉)
- Main sequence lifetime ∝ M/L ∝ 1/M² (more massive = shorter life)
Solar system
- Terrestrial planets: Mercury, Venus, Earth, Mars (rocky, dense, small)
- Gas giants: Jupiter, Saturn (hydrogen/helium, low density)
- Ice giants: Uranus, Neptune (water, ammonia, methane)
- Asteroid belt: Between Mars and Jupiter
- Kuiper belt: Beyond Neptune, includes Pluto
- Oort cloud: Spherical shell, source of long-period comets
- Planet distances: Mercury 0.4 AU, Venus 0.7, Earth 1, Mars 1.5, Jupiter 5.2, Saturn 9.5, Uranus 19.2, Neptune 30
Cosmology
- Big Bang: ~13.8 billion years ago
- CMB (Cosmic Microwave Background): Radiation from 380,000 years after Big Bang, ~2.7 K
- Dark matter: ~27% of universe, doesn't emit light, detected by gravity
- Dark energy: ~68% of universe, causes accelerating expansion
- Observable universe radius: ~46 billion light-years
Common mistakes
- HR diagram temperature axis is REVERSED (hot on left)
- Confusing apparent vs absolute magnitude
- Forgetting Wien's law gives wavelength in meters
- Using wrong units in Kepler's 3rd law