Markus, twelve yeras ago I red the 6th edition of this book
https://www.amazon.de/Astronomie-kos...4955030&sr=8-3
which came with a 12 or 18 months subscription to online tutoring and questionaires, and I really worked through it, quite disciplined and with regular time table per week as if I were studying. It is not a scientific styuding with plenty of mate,matics and abstract physics, more for the ambitous hopbby astronomner and interested layman - but for the usual standards of these ausdience it was - in the 6th edition - on very good niveau. I do not know what the currently actual format of the 9th edition is like, I heard the text suffers from politically correct gender reformulations, but I cannot comment on it, I dont know it. The book I had I oikekd a lot, and the online course ran smooth and well for me.
You might want to check out the English edition of the current version, if you want to examine astronomy a bit deeper and more organised. For not truly professional needs and demand, this book is probably the best the interersted layman can get.
Be adviose dhowever that the English editions now seem to offer various combionations of packages, some only with the book, some only offering access to the online course, some offering both (as I got it 12 years ago, it was the only avialable option back then). Also, apparently they now offer different versions of the book itself. I found the situation quite confusing when I checked for the English books, thats why I give you the German one. In German, 9th edition is the available. From here you can search and check yourself, if you are interested.
Myself, I completed the "curriculum" to maybe around 85%, then real life troubles and a year-long court battle distracted me and took my free energy, and when I came back to it two years later, the online subscription was all consummed up. Still, I liked that approach tremendously. I still have five notebooks (paper) with my own handwritten summaries of every chapter, and answers for the "tests", and my own notes. It was real and true home schooling, imo at its best.If I look at all that paperwork I could fall to the illsuion that I acutally "studied" astronoymn at unioversity!
the letdown is that I never had much to do with astronomy, so I have forgotten so very much of what I have learned back then. Terrible. Knowledge that does not get used, slowly fades again. Its frustrating. Same wioht general books on pohysics I have red. All the details disappeard again in an ocean of "forgetness". Age sucks.
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