Describing Chandra's High Energy Visuals

Kimberly Arcand, Megan Watzke

The Chandra visual description program is an accessible digital project to help connect users — particularly those who are blind, have low vision, or have different learning needs — with the science of NASA’s Chandra X-ray Observatory. Launched in January 2021, the project provides detailed verbal descriptions of Chandra and multiwavelength data (primarily images and data-driven movies or sonifications, as well as illustrations when required) as they are released in real-time. The information is provided in both text and audio formats, and used as alternative texts for web and social media platforms. The audio recordings have also been concatenated into a podcast XML feed after obtaining user feedback. (XML feed)

This project was created with J.J. Hunt and Christine Malec (subject matter experts in science communication, verbal description and/or the blind and low vision communities), Chandra visualization scientist Dr. Kimberly Arcand, and Chandra press scientist and astrophysicist Dr. Peter Edmonds. These user-tested materials have been informing how other Chandra captions or descriptions for non-experts are written for overall improvement to accessibility and inclusion.


The Chandra team has had many years of experience creating descriptions of visualizations that were verified by astrophysics experts. However, the nature and complexity of the Chandra images, including those combined with data from other telescopes, provided additional challenges to usefully portray them for people who are blind or have low vision. In consultation with an audio description consumer and writer who is also blind, it was clear that a unique approach was required to best serve those communities. The project members went through layers of experimentation and revision to refine several elements for this project.

For example, in describing the world around us, there is a shared lexicon of meaning for objects and spatial concepts. When describing images that result from data normally not visible to humans, specifically, and that describe sometimes esoteric or abstract processes, mainstream description techniques fell flat, according to our project research.

Two main issues became clear: First, simply describing the image as it appears, without its scientific meaning, was not helpful and was unsatisfying for audiences who are blind or low-vision. A more useful approach resulted from integrating Chandra’s verbal explanations of the scientific phenomena along with descriptions of what the visual viewer was seeing in the presented image. Typically, descriptions can exist alongside, but be displayed separately, from the scientific narrative. In order to be comprehensible to someone experiencing the image without sight, however, the visual description and explanation has to be integrated in a unique way.

Second, style is extremely important. For a non-scientist, these data can be dense, rich, complicated, abstract, or, in short, challenging to comprehend. Pairing this kind of information with visual description complicates the process further. In consultation over several images, we developed a writing style with short sentences, numerous commas, and frequent use of proper nouns. This style helps by delivering ideas in discrete packages that are easier for listeners to parse. Relatively small changes such as minimizing use of the word “it” and replacing it with the proper name of the object freed the user’s mind from focusing on the meaning of the sentence itself, enabling more concentration on understanding the concepts being discussed. Likewise, shorter sentences with built-in pauses created by commas helps the mind have time to take in what is being presented. Such changes can also help search engine optimization (SEO) results for websites.

Since we began implementing these visual descriptions in Chandra Communications releases, we have continued to survey the results among the audiences we are trying to reach. We have presented the project at numerous community events, particularly for participants who are blind or low vision, with highly positive feedback. As we learn more about the needs and wants of these communities, we will adapt further to refine our best practices. Moreover, we have begun to share what we have learned with other NASA and astronomy communications professional groups and are developing a “master class” workshop to help other groups apply these techniques for their own programs. There is a keen interest throughout the field to be more responsive to what have traditionally been underserved audiences. We are excited that Chandra is helping to address some of those needs and provide new paths to communication and engagement.


  1. Cat’s Eye sonification
    The Cat’s Eye video features a static image of an ethereal shape surrounded by concentric circles. The shape is the Cat’s Eye nebula, a huge cloud of gas and dust blown off of a dying star. The concentric circles are bubbles expelled by the star over time. The dust cloud resembles a translucent pastry pulled to golden yellow points near our upper right and lower left, with a blob of bright purple jelly inside the bulbous pale blue core. The jelly-like center represents X-ray data from Chandra.

    The outer cloud and translucent circles represent visible light data from the Hubble Space Telescope. As the video unfolds, a white line emanating from the center of the nebula scans the image in a circle, like the second hand on a clock, or the radial arm on a radar screen. The more of the nebula that’s in its path, the richer the accompanying sound. Light that is farther from the core has a higher pitch than light that is close to the core. X-rays are represented by a harsher sound, while visible light data sound smoother. The concentric circles create a constant hum interrupted by a few sounds from spokes in the data. Additional videos feature Cat’s Eye images and audio from separated X-ray and optical data sets.
  2. V404 Cygni image
    This composite image features a series of incomplete concentric rings in a black field dotted with gleaming white, yellow, and golden stars. The giant rings are light echoes, a phenomenon similar to echoes from sound waves bouncing off of hard surfaces. These light echoes were produced when X-rays burst from gas near a black hole at the center of the image and bounced off of cosmic dust clouds. Black holes themselves, like this one in the V404 Cygni binary system, are invisible.

    Here, the X-rays are rendered as hazy neon blue rings. The smallest, near the center, is the brightest and the most substantial. The remaining concentric rings are somewhat wispier, but are much larger, and extend beyond the edges of the image. These rings are not clearly defined like the clean ridges on a record album. Instead, they appear vague and blurred, resembling curving tire marks left in wet snow. The rings are incomplete, with gaps at our upper right, and upper left. A string of gaps appears in a horizontal line across the middle of the image, as if portions of the neon blue X-ray rings were removed with a straight swipe of an eraser. These gaps show the edges of Chandra's field of view during the observations, or the sections of the field Chandra did not observe.