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# Preface
I am writing this book because I want to learn quantum astronomy.

At first I looked for a textbook that began with observations: real astronomical data first, then coherence functions, photon statistics, quantum estimation, and instrumental limits introduced as the data demanded them. I did not find that book. The relevant material certainly exists, and many papers and monographs are excellent, but the subject is scattered across statistical optics, quantum optics, interferometry, high-energy astrophysics, cosmology, and quantum information.

So I decided to write the book myself, and to treat the writing as part of the learning. The book is still being revised because I am still learning.

<div class="signature">Yu Wang<br>July 2026</div>