Those of us who write nonfiction often use sidebars to include information that isn’t “on topic” enough to go into the main text but can still provide insight into the topic. In Ancient Maya, my chapter on Maya society includes sidebars on murals that show life in the marketplace and jade. In The Attack on Pearl Harbor, the chapter on US intelligence efforts has sidebars on Japanese censorship, how the US gathered information on Japanese cryptanalysis, the US military belief that an attack was impossible and how long it took the US to decrypt Japanese messages.
Coming up with these sidebar topics can be a lot of fun but sidebars intimidate new nonfiction writers. The most common question? “How do I format them? Where do I include them in the manuscript?” When a book has chapters, I simply include them at the end of the chapter. The sidebars are double spaced and otherwise formatted just like the other text.
The voice of your sidebar is most often the same as the voice in your main manuscript. If, in the book design, the sidebars are printed on the page as inserts from academic notes, newspaper stories or something similar, the tone and voice would be consistent with whatever they were supposed to be. This might mean that the voice would be more academic or, in the case of “yellow” journalism, skewed in that direction.
When it comes to the word count, follow the publisher’s guidelines. For Red Line and ABDO, I include the word count of the sidebars in the count for the chapter. Other publishers may have other requirements.
Sidebars are a great way to give your reader just a bit more information. As I research, I keep track of things that are interesting but are just a bit off topic. Eventually, many of these things end up becoming sidebars.