Astronomy Stack Exchange
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Question-and-answer site where working astronomers and physicists answer technical questions about orbits, stellar physics, observation and cosmology. Browsing highly voted answers shows how practitioners reason through problems and where common misconceptions break down.
More resources on Astrophysics
PBS Space Time
A long-running PBS YouTube series hosted by astrophysicist Matt O'Dowd, working through black holes, general relativity, quantum field theory, and cosmology at a level that uses real equations and cites the underlying papers.
nasa.gov
NASA.gov is the official site of the U.S. space agency, offering mission news, research results, data, and STEM education resources. It features engineering articles, technical briefs, simulations, multimedia, and classroom materials for students and educators.
The Astrophysical Journal
Peer-reviewed journal published by the American Astronomical Society through IOP, carrying primary research on stars, galaxies, cosmology and high-energy phenomena. Reading it exposes you to how astrophysical results are actually reported, argued and cited.
NASA Astrophysics
NASA's astrophysics division portal, covering current missions such as Hubble, Webb and Chandra alongside mission data archives and science summaries. Useful for tracking what instruments are observing now and finding the datasets behind published results.
Cosmic Origin of the Chemical Elements (MIT RES.8-007)
Twelve short lecture videos, about 1.4 hours in total, on where the elements came from: light nuclei made in the Big Bang, fusion in stars, supernova nucleosynthesis, and how spectra of the oldest stars record the universe's chemical enrichment.
An Introduction to Modern Astrophysics
Comprehensive undergraduate textbook covering stellar structure, evolution, binary systems, the interstellar medium, galaxies and cosmology. Working through it gives you the physics and mathematics needed to read research-level astrophysics and to solve quantitative problems about stars.