Astronomy
The book is comprehensive in topic with depth of coverage suitable for general education students in either a one or two semester course.
The text includes chapter outlines and overviews, learning objectives for each section within the chapter, and a glossary of key terms and summary following each chapter. In addition there is a list of articles, websites and videos for each of the chapters, and a set of collaborative group exercises and various kinds of review questions to help students understand the material.
There is no glossary at the end of the text, but since the book is designed to be used in modular form it is probably more useful to have a glossary associated with the chapters where the terms appear.
The depth of the coverage is adequate for the general education population, but probably not sufficient for students majoring in astronomy or physics. It includes math where appropriate, but it is not a major focus and not necessary to comprehension of the basic concepts in the book. The coverage of basic physics is less than in some of the other introductory textbooks, but again seems to be adequate for this level. One thing I like is that the authors introduce physics concepts in early chapters, then refer back to them when needed and extend the concepts in chapters where understanding such things as how spectra form and the role of density are crucial.
I found that the index is minimal and lacks important terms that would help the student navigate the text as a whole. It may be because the book is new, it was published in final form near the end of Fall 2016.
The websites and links cited throughout each chapter are very helpful when students read it in pdf on-line and can click directly on the links to get simulations, additional images and relevant web pages. My concern here would be that if the links are not reviewed frequently students will be frustrated with "dead" links and references. However, the linked resources are excellent for students who see themselves as "visual" learners, and are more easily engaged with videos and interesting pictures.
My reading so far hasn't revealed any inaccuracies beyond some minor typos that one would expect with any newly published text.
In general the authors seem to be good at presenting current understanding of astronomical processes, as well as mentioning areas where knowledge is incomplete. Students often wonder why they should study science when what was "correct" today, is discarded tomorrow. The authors deal in a few sentences with the question of Pluto's status as a planet and make a case for it being classified as a dwarf planet. It might have been useful to use this topic as a route into talking about classification systems and their role in scientific understanding and discovery. While this question is not addressed in depth, links to other materials, including a debate about planetary designation, are useful to instructors who want to pursue the idea of definition and classification.
The text is as up-to-date as possible in a field as volatile as astronomy. The text itself includes information about the New Horizons mission to Pluto in 2016, the first measurement by LIDO of gravitational waves. The authors have promised new editions and there is currently an errata list on the textbook OpenStax page. If, as suggested, the book is regularly revised, and the links (which are highly like to move or become outdated) are checked, the book should stay at least as current as any textbook in print.
The book is written at a clear and accessible level for non-science majors. Frequent analogies help those new to astronomy to build useful mental images. Fro example, when discussing the age of the universe, the authors make an analogy where students leave a party and drive home at a constant speed, then by working back can figure out when they left the party.
Technical terms are generally explained in the context of the chapters, which means that, for the most part, chapters, and even sections can stand alone.
The book has a standard format for each chapter which repeats consistently. This makes it easy to know where to start if you want to find something like the definitions or and overview of section learning goals. The technical terminology is at the same level throughout which is very helpful since the number of new words introduced in a typical astronomy course can be daunting. It appears that most terms are defined as they arise, and defined in slightly different terms in new contexts in other chapters.
I used the first half of the text, the solar system chapters, in a course in fall 2016. The text was easy to organize around the topics in the order I wanted to cover them since the table of contents links directly to the chapters. I wanted more background on solar system formation and wa able to pull in part of Chapter 21 which deals with the birth of stars and the discovery of planets outside the solar system, that, combined with a section of Origin of the solar system in Chapter 7 and yet another section on the topic in chapter 14 gave enough reading for the students to begin thinking about how a solar system might form and how we would know. In some ways it might have been better to have just one chapter on this topic. On the other hand, it is useful to have sections on the topic in various chapters so that each can stand alone. I like the feeling of freedom I have with this text for that reason.
One downside is that the text is Pdf making it hard to rearrange in a sequence that might fit my course objects better for some topics. After using the book I may at some point request a "custom" copy, but students seemed to do well with it in the form it has now. The text is easy to use in "bite-sized" chunks, but also has enough from from section to section that it doesn't feel like a random selection of factoids. The themes of science process, how we know, and short biographical portraits of influential people in the field all serve to connect the pieces together and at the same time allow the book to feel unified even when skipping chapters or sections.
For the most part topics are presented in the same order as in any one of a dozen other standard astronomy textbooks. There is perhaps less emphasis on basic classical physics in stand-alone chapters than in most other tests, but much of what is needed in terms of the basics is also woven in where it is relevant. Because I teach a two semester course those chapters must be repeated in each semester which is tedious for students who take the courses in sequence. I like having two chapters on light, one concentrating on spectra and what light is, the other on spectra and how it is used in stellar astronomy. Similarly, the topic of other solar systems comes up twice, once in the first half when discussing solar systems and then again in the last chapter of the text in the context of life in the universe.
I regularly rearrange the order in which students are introduced to material, mostly because I prefer not to spend a large part of the semester preparing students to understand astronomy instead of having them get a good introduction to what they are interested in first, then going back to ask the how and why kinds of questions. This book works well for that when it is in digital form.
The pdf version seems to work very well. I use an LMS extensively and posting the links to the chapters for each week's work seems to be useful. The downside is the problem I see with any e-text, that flipping through pages to look for something to review or study further is not easy. But overall the text is easy to read in pdf form and has the advantage of being able to increase the size of images and graphs to make them more readable.
In print form I see some oddities. There are occasional large expanses of white space for no apparent reason, most likely because an illustration comes before or after. Now and there there are "orphan" ends or beginning of sentences that didn't quite fit on the page before or after. But images and graphs and diagrams are all large enough to read easily and are more or less in line with the text that references them.
The few small errors I found were mostly typos it appears and the errata list on the book's web pages clarifies the ones that have turned up that are more significant.
While the text is not overtly insensitive or offensive, I did find that the majority of faces in the images were European and American males. This is probably to be expected historically, and while there were several nice bios of women, Margaret Gelle and Andrea Glez for example, the women who are documented in historical astronomy, Annie Jump Cannon, Cecilie Payne Gaposchkin, and Caroline Herschel are present in small pictures only, in spite of the fact that there are interesting and relevant stories about each. William and Margaret Huggins appear in a small image as well and I would be interested in knowing more about both of them. Subrahmanya Chandresekhar has a nice picture and story, and John Goodrichke- who was deaf are representatives of those who come from a different culture and overcame physical difficulties to work in the field, but I do think the authors could have done better with this aspect. There are some nice bits of poetry and some questions that relate astronomy to various works of literature and art, but I think even more of that would benefit a readership that often questions how astronomy can possibly be relevant.
I have rated this book at the top in most categories, partly because there really is nothing else quite like it and it sets a high standard. It is certainly time for texts that can be used in a flexible modular way at low, or no cost. I imagine the text will continue to evolve and improve as long as there are resources to support this kind of effort.
One difficulty personally is that we used a different text for our online course and now will need to redo the narrated powerpoints in order to switch to this text. The powerpoints these authors supplied are a good start. I am also looking for a homework resource such as Mastering Astronomy that can be paired with this course at low cost. Re-designing the courses to use Open Educational Resources is a work in progress. I am extremely happy to have found a textbook as useful as this one to begin with.