I've collected a considerable library of references over the years. Many of them are stored on my phone. The first three below are great places for ideas for projects on any of the sciences.
Aimed toward school kids developing science projects, the many ideas on this website are useful for any explorer of the sciences.
I've mentioned this site before. One cool thing about it is their repository of manuals from old science kits, back when they were not lame.
All of MIT's course materials including many of the textbooks, lecture notes, lecture videos, and even a few lab guides.
Olcott, William (1907) A Field Book of the Stars (available in various forms at the Gutenberg Project site).
A nice thing about old do-it-yourself books is that they were printed back when people had to use what they had at hand to do things. You won't find out anything about black holes but there is all kinds of observational information.
NASA Imagine the Universe Dictionary online at https://imagine.gsfc.nasa.gov/resources/dictionary.html useful for figuring out what you're talking about and how to talk about it.
Astronomy Merit Badge Handbook
What do you need to know to prove you know the Stars? Ask the Boy Scouts! You can look at their merit badge guides at https://www.scouting.org/programs/scouts-bsa/advancement-and-awards/merit-badges
The Wikipedia offers textbooks on many topics including astronomy at https://en.wikibooks.org/wiki/Main_Page
Astro-Tom provided a list of New General Catalog objects and their observational data at http://www.astro-tom.com/technical_data/files_to_download.htm . It's an Excel spreadsheet so you'll need a spreadsheet app that's compatible with Excel.
Tonkin, Stephen (2007) Binocular Astronomy, Springer-Verlag, London. A guide to exactly what I'll be doing in 2020 - low power astronomical observation.
Also from Astro-Tom (see BEST-NGC.XLS above for the link), a list of data for the brightest stars in the sky.
Cambridge Illustrated Dictionary of Astronomy
Mutton, Jacqueline (2007) Cambridge University Press.
A beautifully Illustrated dictionary of astronomical terms and bodies.
Dictionary of Geophysics, Astrophysics, and Astronomy
Matzner, Richard A. Ed.(2001) CRC Press. Articles by 52 acknowledged experts in the field.
Geometry_of_science.xls (https://www.csun.edu/science/ref/spreadsheets/xls/) among many useful Excel spreadsheets, this one has a section of the intensity of light on the planets.
HERSCH.xls (http://www.astro-tom.com/technical_data/files_to_download.htm) another spreadsheet from Astro-Tom. It's the Herschel 400 listing.
Isaac Asimov's Guide to Earth and Space
Asimov, Isaac (1991) Fawcett Books
A lot of astronomical, physical, and geological information from the master of scientific popularization.
And more spreadsheets from Astro-Tom providing much observational data.
Your New Telescope: The Good, The Bad, and the Ugly
This is a page by Tom Koonce on the Astro-Tom website (http://www.astro-tom.com/download/presentations/new_telescope.pdf).
Physics - From Stargazers to Starships
Stern, David P. And Alex A. Zaliznyak (2023) CK-12.
This CK-12 textbook focuses on the physics of space, written at a beginner's level and in a very readable style. How did astronomy get started and how did it get to where it is today?
Schaum's Outline: Astronomy
Palen, Stacey (2002) Schaum's Outlines: Astronomy. McGraw Hill.
As always, Schaum's Outlines are great study resources, dense with information, examples and problems, worked and unworked.
Taki's 8.5 Magnitude Star Atlas
Toshimi Taki (2006) Can be downloaded from Taki's website with lots of other information here http://www.takitoshimi.shop/
MIT 12.409 Hands-On Astronomy
Among MIT's many other online courses is this beginner's astronomy course. Get it at https://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-409-hands-on-astronomy-observing-stars-and-planets-spring-2002/
Star Date Online
This website is great for keeping up with what's going on I'm the sky and in astronomy.
A Simple Guide to Backyard Astronomy Using Binoculars or a Small Telescope
Beigel, Carol (2007) available at www.carolrpt.com/astroguide.htm (accessed 10/17/19)
This is a nicely packaged reference for the amateur astronomer.
Night Sky - A Falcon Field Guide
Nigro, Nicholas (2012) Morris Book Publishing.
All the Falcon Guides are fairly complete, portable, and inexpensive. Not a lot of technical information, but that's why all the other references.
Sky Watching. The Teaching Company
Alex Filippenko (2011)
I highly recommend the lecture series (buy it when it's on sale). It's beautiful and packed with information from someone who knows what they're talking about, but the course guide that comes with the videos should definitely go with you into the field.
A Visual Guide to the Universe
The Teaching Company
David M. Meyer (2014)
A gorgeous guide to the Universe through the lenses of our orbiting telescopes.
Understanding the Universe: An Introduction to Astronomy
The Teaching Company
Alex Filippenko (2007)
The astronomy course from the teaching company. It's a great start to you career in astronomy.
I'm all about getting out of the house to learn about the world, but the best place to start is in the library...yours or the one down the street. Get a preview before you hit the trail.