Anna Rosen · San Diego State University · Spring 2027
Astronomy for Science Majors
A quantitative introduction to astrophysics — learn to extract physical insight from limited observations using mathematics and physics.
ASTR 2015 modules · 24 lessons
Course operations
◆ Due Soon
Homework 1 — Tools of the Trade + Gravity & OrbitsProblem set9 problems2027-02-13
Course method
How you will think in this course
This is not a "tour of the cosmos" course.
◐Decode observations
- ObservableWhat we measure (parallax angle, color, line spectrum, orbital period)
- ModelWhat we believe (geometric, atomic, gravitational, statistical)
- InferenceWhat we can claim (distance, T, M, composition, L)
∑Build a portable toolkit
Dimensional analysis, ratio method, order of magnitude estimation, and unit conversions — reasoning skills that outlast any single equation.
◇Pressure-test models
What we leaned on; where it breaks
The Course · 5 modules
01FoundationsThe shared toolkit and vocabulary every later module assumes — what astronomers measure, the reasoning tools that turn those measurements into physical claims, and the habits (units, ratios, estimation) that keep the physics honest.Weeks 1–34 lessons02Discovering the HR DiagramWhat a star's light reveals about it. From distance and parallax through surface flux, color, spectra, and stellar masses, this module builds the observational toolkit that turns brightness and color into temperature, luminosity, and radius — and assembles them into the Hertzsprung-Russell diagram.Weeks 4–65 lessons03How Stars WorkWhat holds a star up and what powers it. From gravity and force balance we build the equations of stellar structure — hydrostatic equilibrium, the virial theorem, nuclear energy generation, and radiation transport — and read the main sequence as a one-parameter family in mass.Weeks 7–95 lessons04How Stars Live and DieHow stars live and die. The mass limits that bound stardom, the journey off the main sequence, the quantum degeneracy that sets the Chandrasekhar limit, the deaths of giants in supernovae, and the compact remnants where gravity finally wins — white dwarfs, neutron stars, and black holes.Weeks 10–125 lessons05Galaxies & CosmologyZooming out from individual stars to the systems and spacetime that contain them. Galaxies are evolving ecosystems of gas, stars, and feedback; dynamics weighs what light cannot show and reveals dark matter; and the expansion of spacetime — Hubble's law, redshift, the cosmic microwave background, and the Big Bang — sets the stage on which all of it plays out.Weeks 13–155 lessons