AST study guide
AST · Work through your exam, one topic at a time.
The Astronomy Subject Test (AST) is a standardized, multiple-choice examination that assesses a candidate's grasp of astronomy at the undergraduate level, spanning astrophysics and cosmology, stellar structure and evolution, galaxies, planetary science, instrumentation, celestial mechanics, the interstellar medium, and the underlying physics. It is typically taken by students preparing for graduate study or by candidates who need an external, comparable measure of their astronomy knowledge. The AST study guide has 8 sections and about 1,723 words.
01Astrophysics and Cosmology
A candidate must be fluent in the distance ladder (parallax, main-sequence fitting, Cepheids, Type Ia supernovae), redshift and the Hubble-Lemaître law, the thermal history of the universe, nucleosynthesis, and the evidence base for dark matter and dark energy. Know the cosmic microwave background's blackbody temperature (about 2.725 K) and its acoustic peaks, the meaning of the scale factor, and the difference between luminosity distance and comoving distance.
262 words, about 1 min02Stellar Structure and Evolution
Master the four stellar structure equations (hydrostatic equilibrium, mass continuity, energy transport, and energy generation), the equation of state across regimes, opacity sources, and the Hertzsprung-Russell diagram. Know the main sequence's mass-luminosity relation (roughly L ∝ M^3.5), the proton-proton chain versus the CNO cycle, and the endpoints of evolution: white dwarfs, neutron stars, and black holes, with the Chandrasekhar limit near 1.4 solar masses.
231 words, about 1 min03Galaxies and Galactic Structure
Know Hubble's morphological classification, the Milky Way's components (thin and thick disk, bulge, stellar halo, dark-matter halo), rotation curves, and the Tully-Fisher and Faber-Jackson relations. Understand spiral density waves, the role of mergers in ellipticals, active galactic nuclei and their unification, and the metallicity and kinematics that separate populations.
221 words, about 1 min04Solar System and Planetary Science
Understand solar system formation from a protoplanetary disk, the frost line, accretion and differentiation, Kepler's laws applied to orbits, and the terrestrial versus giant planet dichotomy. Know orbital resonances, tidal locking, the Roche limit, impact cratering, and atmospheric escape.
221 words, about 1 min05Observational Astronomy and Instrumentation
Know telescope optics (refracting versus reflecting, focal ratio, plate scale), resolution limits from diffraction and seeing, detector characteristics (quantum efficiency, read noise, dark current), and photometric systems and filters. Understand spectroscopy basics: dispersion, resolution R = λ/Δλ, and line broadening.
192 words, under 1 min06Celestial Mechanics and Dynamics
Master Newtonian gravity, Kepler's laws, orbital elements, the vis-viva equation, and energy and angular momentum conservation. Understand two-body and restricted three-body problems, Lagrange points, perturbations, precession, and tidal forces.
188 words, under 1 min07Interstellar Medium and Star Formation
Know the phases of the interstellar medium (molecular clouds, cold and warm neutral gas, ionized regions, hot corona), dust extinction and reddening, and the Jeans criterion for collapse. Understand molecular cloud structure, turbulence, magnetic support, and the stages from core collapse to protostar, disk, and outflow.
210 words, about 1 min08Physics Fundamentals Applied to Astronomy
Be solid on mechanics, thermodynamics, radiation, and atomic physics as applied to astrophysics: blackbody radiation and the Planck, Stefan-Boltzmann, and Wien laws; the Doppler effect; atomic energy levels and spectral lines; the ideal gas law; and conservation laws. Understand radiative transfer basics, optical depth, and the difference between emission and absorption.
198 words, under 1 min