DSST Astronomy flashcards
DSST Astronomy · Build recall with a focused review session.
34 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Kepler's second law
- A line joining a planet and the Sun sweeps out equal areas in equal time intervals, so orbital speed is highest at perihelion and lowest at aphelion.
- Escape velocity formula
- The minimum speed to escape a body's gravity is v = sqrt(2GM/R), where G is the gravitational constant, M is the body's mass, and R is its radius.
- Roche limit
- The distance from a primary inside which a satellite held together only by gravity is torn apart by tidal forces, forming a ring system.
- Angular momentum conservation
- In a central force field, the product m v r sin θ stays constant along an orbit, so a planet moves faster when closer to the Sun.
- Globular cluster
- A dense, spherical group of 10^5 to 10^6 old, metal-poor stars that orbits in a galaxy's halo; Omega Centauri is a prominent example.
- Eclipsing binary
- A binary star system whose orbital plane is nearly edge-on to Earth, producing periodic dips in brightness that reveal stellar radii and orbital properties.
- Local Group
- The galaxy group containing the Milky Way, Andromeda, Triangulum, and dozens of dwarf galaxies, spanning roughly 3 megaparsecs.
- Open cluster
- A loose group of 10^2 to 10^3 young, metal-rich stars formed together in a galactic disk, such as the Pleiades.
- Rayleigh criterion
- The angular resolution limit of a telescope is θ = 1.22 λ / D radians, where λ is wavelength and D is aperture diameter.
- Light-gathering power
- A telescope's ability to collect light, proportional to the square of its aperture diameter; doubling the aperture quadruples the collected light.
- Adaptive optics
- A technique using a deformable mirror and wavefront sensor to correct atmospheric turbulence in real time, sharpening images from ground-based telescopes.
- Reflecting telescope
- A telescope using a concave primary mirror to gather and focus light; it avoids chromatic aberration and allows very large apertures.
- Nebular hypothesis
- The model that the solar system formed from a collapsing, rotating cloud of gas and dust that flattened into a disk and accreted into planets.
- Terrestrial planets
- Mercury, Venus, Earth, and Mars: small, rocky, dense inner planets with few or no moons and no ring systems.
- Jovian planets
- Jupiter, Saturn, Uranus, and Neptune: large, low-density outer planets rich in hydrogen and helium, with many moons and ring systems.
- Venus greenhouse effect
- A runaway greenhouse warming caused by a thick carbon dioxide atmosphere that raises Venus's surface temperature to about 730 K.
- Main-sequence lifetime
- The time a star fuses hydrogen in its core, roughly 10^10 (M/M_sun)^−2.5 years; more massive stars live shorter lives.
- Chandrasekhar limit
- The maximum mass of a white dwarf, about 1.4 solar masses, beyond which electron degeneracy pressure cannot support the star.
- HR diagram
- A plot of stellar luminosity versus temperature or spectral class; most stars lie on the diagonal main sequence, with giants and white dwarfs off it.
- Type Ia supernova
- An explosion of a white dwarf that accretes too much mass in a binary system; its consistent peak luminosity makes it a standard candle.
- Galactic rotation curve
- A plot of orbital speed versus distance from a galaxy's center; it stays roughly flat at large radii, implying a massive dark matter halo.
- Population II stars
- Old, metal-poor stars found in galactic halos and globular clusters, formed early in a galaxy's history.
- Interstellar reddening
- The preferential scattering of shorter wavelengths by interstellar dust, making distant stars appear redder than their true color.
- Sagittarius A*
- The compact radio source at the Milky Way's center, identified as a supermassive black hole of about 4 million solar masses.
- Hubble's law
- Galaxies recede with velocity proportional to distance: v = H0 × d, where H0 is about 70 km/s/Mpc.
- Cosmic microwave background
- Relic radiation from recombination about 380,000 years after the Big Bang, now cooled to a nearly uniform 2.725 K blackbody spectrum.
- Critical density
- The density ρ_c = 3H0^2/(8πG) that makes the universe spatially flat; current matter and dark energy together nearly equal it.
- Dark energy
- A mysterious component with negative pressure that makes up about 70% of the universe's energy budget and drives accelerated expansion.
- Parallax distance formula
- Distance in parsecs equals 1 divided by the parallax angle in arcseconds; a star with 1 arcsecond parallax is 1 parsec away.
- Distance modulus
- The difference between apparent and absolute magnitude, m − M = 5 log10(d) − 5, where d is distance in parsecs.
- Cepheid period-luminosity relation
- The period of a Cepheid variable star is tightly correlated with its intrinsic luminosity, allowing it to serve as a standard candle.
- Habitable zone
- The range of orbital distances around a star where a planet's surface could sustain liquid water, depending on stellar luminosity.
- Drake equation
- A formula estimating the number of communicating civilizations in the galaxy as the product of star formation rate and several poorly known fractions.
- Fermi paradox
- The contradiction between the high probability of extraterrestrial life and the absence of observed evidence for it.