Ask HN: How can I get basic astrophysics knowledge?

Armchair astrophysics lover here. FWIW: I've always felt like PBS Space Time on youtube is one step short of a bachelors in astrophysics, at least, it's very good for picking up the abstract ideas around many of the major principles and then you can go research them deeper via reading papers.

Search youtube for the theoretical minimum https://youtu.be/iJfw6lDlTuA its a whole playlist for quantum mechanics, Wilberger also has videos on hyperbolic geometry and relativity

I would suggest “An Introduction to Modern Astrophysics” by Bradley W Carroll and Dale A Ostlie.

It's hard to know what your current knowledge level is without more information, but it sounds like you're trying to develop a good background more just to dive into areas that seem fun to explore as a hobby, rather than focused study-- so I'm suggesting things that lead to more exploration.

A few of the resources below are good backgrounds, and Wikipedia is great for filling in your knowledge. Then to find interesting things to spark your hobby interest, I'd recommend following astronomers and astrophysicists on twitter, which will also help point you to interesting papers (which may take a lot of referencing Wikipedia to understand).

You'll need at least a little quantum physics to have some things make sense, so it's worth getting that from some of the links people mentioned below if you don't already.

If you don't know the topics below in detail, learn it from wikipedia to make sure you understand topics well enough to explore (in rough order): https://en.wikipedia.org/wiki/Astrophysics - links to all the rabbit hole topics you may want to explore https://en.wikipedia.org/wiki/Astronomical_spectroscopy https://en.wikipedia.org/wiki/Redshift https://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_di... then look at all the "see also" topics on the last one to go over basic star physics Then for dramatic events: https://en.wikipedia.org/wiki/Nova https://en.wikipedia.org/wiki/Luminous_red_nova https://en.wikipedia.org/wiki/Supernova https://en.wikipedia.org/wiki/Gravitational_wave

Some twitter folks for key topics (and you can find interesting papers and other twitter folks from there): @badastronomer (great for pointers/explanations for lots of topics) @astrokatie (cosmology) @nasaSun (the Sun) @jannaLevin (black holes, gravity astronomy) @matt_of_earth (host of PBS Spacetime, which someone else mentioned) @ajpizzuto (neutrino astronomy)

Well, originally astrophysics involved staring at the sky for long periods and coming up with hypotheticals and maybe even theories about the movement of celestial bodies? it was very inexpensive and led to the fame of people like Galileo. Later, staring at the night sky was eclipsed a little. Folks like Gerard P. Kuiper used telescopes and made more detailed observations. The feild then rapidly became more complicated, but staring at the sky and eventually mastering the skill of designing and building your own detectors (what we in the feild refer to as "remote sensing") remains a proven method.

I wish you all the good luck in the universe :)