The Aesthetics of Astrophysics: How to Make Appealing Color-composite Images that Convey the Science

Astronomy has a rich tradition of using color photography and imaging, for visualization in research as well as for sharing scientific discoveries in formal and informal education settings (i.e., for "public outreach.") In the modern era, astronomical research has benefitted tremendously from electronic cameras that allow data and images to be generated and analyzed in a purely digital form with a level of precision not previously possible. Advances in image-processing software have also enabled color-composite images to be made in ways much more complex than with darkroom techniques, not only at optical wavelengths but across the electromagnetic spectrum. And the internet has made it possible to rapidly disseminate these images to eager audiences. Alongside these technological advances, there have been gains in understanding how to make images that are scientifically illustrative as well as aesthetically pleasing. Studies have also given insights on how the public interprets astronomical images, and how that can be different than professional astronomers. An understanding of these differences will help in the creation of images that are meaningful to both groups. In this invited review we discuss the techniques behind making color-composite images as well as examine the factors one should consider when doing so, whether for data visualization or public consumption. We also provide a brief history of astronomical imaging with a focus on the origins of the "modern era" during which distribution of high-quality astronomical images to the public is a part of nearly every professional observatory's public outreach. We review relevant research into the expectations and misconceptions that often affect the public's interpretation of these images.