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OpenStem
@openstem · Joined Jul 2026
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Quiz4 questions
The generalized Kepler's third law for a binary, P² = 4π²a³/[G(M₁+M₂)], differs from the single-planet version primarily by:
AUsing the orbital period squared instead of cubedBIncluding the sum of BOTH stars' masses, since neither can be assumed negligibleCRemoving the gravitational constant G entirelyDApplying only to circular orbits
Astronomy · L4 · Binary Star Systems — 4 Q
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Astronomy · L4 · Binary Star Systems — 4 QQuiz4 questions
The kappa mechanism drives Cepheid pulsation because, in the partial-ionisation zone, compressing the gas:
ADecreases opacity, as in most stellar layers, damping oscillationBIncreases opacity, trapping radiation and driving further expansionCHas no effect on opacity at allDInstantly extinguishes nuclear fusion in the core
Astronomy · L4 · Variable Stars: Cepheids & RR Lyrae — 4 Q
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Astronomy · L4 · Variable Stars: Cepheids & RR Lyrae — 4 QQuiz4 questions
The patched conic approximation makes interplanetary trajectory design tractable by:
AIgnoring gravity entirely during the heliocentric cruise phaseBSplitting the trajectory into separate two-body segments, each dominated by one body's gravity, and matching them at each sphere-of-influence boundaryCAssuming every planet has an identical sphere of influenceDRequiring a full numerical integration of every body's gravity simultaneously
Astronomy · L4 · Interplanetary Trajectory Design — 4 Q
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Astronomy · L4 · Interplanetary Trajectory Design — 4 QQuiz4 questions
The Salpeter initial mass function, dN/dM ∝ M^(−2.35), implies that:
AEvery star-forming region produces exactly the same number of high- and low-mass starsBLow-mass stars vastly outnumber high-mass stars at birthCHigh-mass stars vastly outnumber low-mass stars at birthDOnly stars near 1 solar mass ever form
Astronomy · L4 · Stellar Populations & the Initial Mass Function — 4 Q
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Astronomy · L4 · Stellar Populations & the Initial Mass Function — 4 QQuiz4 questions
Radio telescopes face a harder resolution problem than optical telescopes mainly because:
ARadio waves travel slower than lightBRadio wavelengths are far longer than optical wavelengths, so matching optical resolution needs a far larger dishCRadio dishes cannot be made reflective enoughDThe atmosphere blocks all radio wavelengths
Astronomy · L4 · Radio Interferometry & the EHT — 4 Q
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Astronomy · L4 · Radio Interferometry & the EHT — 4 QQuiz4 questions
In the equilibrium-temperature energy balance, the factor of 4 in T_eq = [(1−A)S/(4σ)]^(1/4) comes from:
AThe planet absorbing sunlight over its cross-sectional area (πR²) but radiating from its full spherical surface (4πR²)BAn arbitrary calibration constant with no physical meaningCThe number of greenhouse gases typically presentDThe planet's rotation period
Astronomy · L4 · Comparative Planetary Atmospheres & Climate — 4 Q
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Astronomy · L4 · Comparative Planetary Atmospheres & Climate — 4 QQuiz5 questions
The restoring force for p-modes is pressure (acoustic waves); the restoring force for g-modes is:
AMagnetic tensionBBuoyancy in a stably stratified regionCCentrifugal force from rotationDRadiation pressure alone
Astronomy · L4 · Asteroseismology & Helioseismology — 5 Q
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Astronomy · L4 · Asteroseismology & Helioseismology — 5 QQuiz5 questions
Astronomers must observe stars near the Galactic Center in the near-infrared, not visible light, mainly because:
AThose stars only emit infrared lightBRoughly 30 magnitudes of interstellar dust extinction make the region essentially opaque at visible wavelengthsCInfrared telescopes have better raw angular resolution than optical onesDSagittarius A* itself only glows in the infrared
Astronomy · L4 · The Galactic Center & Sagittarius A* — 5 Q
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Astronomy · L4 · The Galactic Center & Sagittarius A* — 5 QQuiz5 questions
The coexistence of O₂ and CH₄ in an atmosphere is a stronger biosignature than either gas alone because:
ABoth gases are individually undetectable, so only their sum mattersBThe two gases react and would be destroyed unless something continuously replenishes them — implying an active source, plausibly biologicalCO₂ and CH₄ can only ever be produced by photosynthesisDThe combination has no chemical significance
Astronomy · L4 · Astrobiology & Biosignatures — 5 Q
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Astronomy · L4 · Astrobiology & Biosignatures — 5 QQuiz5 questions
In the lens equation β = θ − (D_ls/D_s)α̂(θ), the term β represents:
AThe observed image position on the skyBThe source's true angular position, had it not been lensedCThe Einstein radius of the lensDThe redshift of the lens
Astronomy · L4 · Gravitational Lensing & Time-Delay Cosmography — 5 Q
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Astronomy · L4 · Gravitational Lensing & Time-Delay Cosmography — 5 QQuiz7 questions
What physical principle underlies electron degeneracy pressure in a white dwarf?
AThe ideal gas law relating pressure and temperatureBThe Pauli exclusion principle, which forbids electrons from sharing the same quantum stateCMagnetic pressure from the star's own fieldDRadiation pressure from residual fusion
Astronomy · L4 · White Dwarfs: Degeneracy Pressure & the Chandrasekhar Limit
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Astronomy · L4 · White Dwarfs: Degeneracy Pressure & the Chandrasekhar LimitQuiz7 questions
What observational property is used to classify young stellar objects into Class 0 through III?
AThe star's total massBThe shape of its spectral energy distribution, tracing how much light escapes at shorter wavelengthsCThe number of planets already formed around itDIts distance from Earth
Astronomy · L4 · Protostellar Evolution: From Collapse to the Main Sequence
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Astronomy · L4 · Protostellar Evolution: From Collapse to the Main SequenceQuiz7 questions
What spectral feature first splits supernovae into Type I versus Type II?
AThe presence or absence of hydrogen linesBThe total explosion energyCThe host galaxy's distanceDThe presence or absence of iron lines
Astronomy · L4 · Supernova Classification: Light Curves & Spectral Types
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Astronomy · L4 · Supernova Classification: Light Curves & Spectral TypesQuiz7 questions
What is a mean-motion resonance?
ATwo orbits with completely unrelated, random periodsBTwo orbital periods forming a ratio of small whole numbers, so gravitational tugs repeat coherently at the same phaseCTwo bodies orbiting in exactly opposite directionsDA resonance that only occurs between stars, never planets or asteroids
Astronomy · L4 · Orbital Resonances, Lagrange Points & the Restricted Three-Body Problem
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Astronomy · L4 · Orbital Resonances, Lagrange Points & the Restricted Three-Body ProblemQuiz7 questions
What does proper motion directly measure?
AA star's true speed through spaceBThe angular rate at which a star appears to move across the skyCA star's speed directly toward or away from the observerDA star's distance from Earth
Astronomy · L4 · Stellar Kinematics: Proper Motion, Radial Velocity & Space Velocity
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Astronomy · L4 · Stellar Kinematics: Proper Motion, Radial Velocity & Space VelocityQuiz4 questions
A planet transiting a star causes a fractional flux dip of ΔF/F = 0.01 (1%). If the star has radius R★ = R☉, what is the planet's radius?
AR_p = 0.1 R☉ ≈ ~11 R⊕BR_p = 0.01 R☉ = 1.1 R⊕ (approximately)CR_p = 0.5 R☉ = 55 R⊕ (approximately)DR_p = R☉ (the planet equals the star in size)
Astronomy · L5 · Exoplanet Detection, Hubble's Law, and the H–R Diagram
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Astronomy · L5 · Exoplanet Detection, Hubble's Law, and the H–R DiagramQuiz3 questions
The net reaction of the pp chain in the Sun converts 4 protons into one helium-4 nucleus and releases approximately how much energy?
A2.2 MeV (a single n–p binding)B8.5 MeV (one alpha decay)C26.7 MeV (total including neutrino losses)D938 MeV (rest mass of one proton)
Astronomy · L5 · Stellar Nucleosynthesis and FLRW Cosmology
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Astronomy · L5 · Stellar Nucleosynthesis and FLRW CosmologyQuiz4 questions
A black hole has mass M = 10 M☉. What is its Schwarzschild radius? (r_s,☉ ≈ 3 km)
A3 kmB30 kmC300 kmD3,000 km
Astronomy · L5 · Schwarzschild Black Holes
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Astronomy · L5 · Schwarzschild Black HolesQuiz4 questions
What physical principle underlies neutron degeneracy pressure?
ACoulomb repulsion between like chargesBThe Pauli exclusion principle forbidding identical fermions from occupying the same quantum stateCThermal (gas) pressure from a hot neutron plasmaDThe strong nuclear force acting attractively at all distances
Astronomy · L5 · Neutron Star Physics
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Astronomy · L5 · Neutron Star PhysicsQuiz4 questions
Why is the mass quadrupole (not the dipole) the lowest-order source of gravitational radiation?
AGravitational dipole radiation is forbidden by momentum conservationBDipole radiation exists but is always too weak to detectCOnly spherically symmetric systems can radiate gravitationallyDThe quadrupole moment is always larger than the dipole moment
Astronomy · L5 · Gravitational Waves
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Astronomy · L5 · Gravitational WavesQuiz4 questions
The horizon problem asks why:
AThe universe is expanding at allBWidely separated, apparently causally disconnected regions of the CMB have nearly identical temperaturesCΩ is measured to be exactly 1DGalaxies are receding from us faster the farther away they are
Astronomy · L5 · Inflationary Cosmology
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Astronomy · L5 · Inflationary CosmologyQuiz4 questions
A flat galactic rotation curve (v(r) ≈ constant at large r) implies which mass profile M(r)?
AM(r) is constant beyond the visible diskBM(r) ∝ rCM(r) ∝ r²DM(r) ∝ 1/r
Astronomy · L5 · Dark Matter Candidates and Evidence
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Astronomy · L5 · Dark Matter Candidates and EvidenceQuiz4 questions
In the ΛCDM hierarchical structure-formation picture, which forms first?
AThe largest structures (superclusters), which later fragmentBSmall dark matter halos, which subsequently merge into larger structuresCFully formed spiral galaxies, directly from the primordial gasDGalaxy clusters, simultaneously with the halos inside them
Astronomy · L5 · Hierarchical Galaxy Formation
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Astronomy · L5 · Hierarchical Galaxy FormationQuiz4 questions
Which line-broadening mechanism has a width that scales with the local gas pressure/density, and so is strongest in dwarf stars relative to giants of the same temperature?
ANatural broadeningBThermal Doppler broadeningCPressure (collisional) broadeningDRotational broadening
Astronomy · L5 · Stellar Atmospheres and Spectral Line Formation
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Astronomy · L5 · Stellar Atmospheres and Spectral Line FormationQuiz4 questions
Roughly what is the Eddington luminosity of a 5 M☉ black hole? (L_Edd ≈ 1.26×10³⁸ erg/s per solar mass)
A~2.5×10³⁷ erg/sB~1.26×10³⁸ erg/sC~6.3×10³⁸ erg/sD~1.26×10³⁹ erg/s
Astronomy · L5 · Accretion Disk Physics
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Astronomy · L5 · Accretion Disk PhysicsQuiz4 questions
What powers the optical/infrared light of a kilonova?
AOngoing nuclear fusion in the ejected materialBRadioactive decay of freshly synthesised, very neutron-rich heavy nucleiCReflected light from the merger's gravitational-wave burstDSynchrotron emission from the relativistic jet alone
Astronomy · L5 · Compact Object Mergers and r-Process Nucleosynthesis
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Astronomy · L5 · Compact Object Mergers and r-Process NucleosynthesisQuiz4 questions
What physically produces the CMB's series of acoustic peaks?
ARandom instrumental noise in CMB telescopesBStanding sound-wave oscillations in the pre-recombination photon–baryon fluid, frozen in at recombinationCDoppler shifts from the Milky Way's own motionDGravitational lensing by foreground galaxy clusters
Astronomy · L5 · The CMB Angular Power Spectrum
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Astronomy · L5 · The CMB Angular Power SpectrumQuiz4 questions
Which observation is most often cited as evidence favouring core accretion over disk instability for giant planet formation?
AGiant planets are found only in binary star systemsBGiant planet occurrence correlates strongly with host-star metallicityCAll giant planets orbit at exactly 5 AUDGiant planets are never found around Sun-like stars
Astronomy · L5 · Exoplanet Formation and Demographics
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Astronomy · L5 · Exoplanet Formation and DemographicsQuiz4 questions
Why are Type Ia supernovae described as a 'delayed' enrichment source, unlike core-collapse supernovae?
AThey occur instantly after star formation beginsBThey require a white dwarf progenitor to first form, then accrete or merge over a broad range of further timescales before explodingCThey only occur in galaxies older than the Milky WayDThey are not actually a source of chemical enrichment
Astronomy · L5 · Galactic Chemical Evolution
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Astronomy · L5 · Galactic Chemical EvolutionQuiz4 questions
What new term appears in the expanding-universe perturbation growth equation that has no analogue in the static Jeans instability analysis?
AA pressure-support termBThe Hubble-drag term 2Hδ̇, which damps perturbation growthCA term for the cosmological constant onlyDThere is no difference between the static and expanding cases
Astronomy · L5 · Cosmological Perturbation Theory
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Astronomy · L5 · Cosmological Perturbation Theory