The Many Colors of Galaxies:
YOU Can Help NASA Decode the Cosmos
In this talk, Rochester Institute of Technology astrophysicist and PhD candidate Sadie Coffin explores what the light from distant galaxies can tell us about the universe—how old a galaxy is, how far away it lies, and what the cosmos looked like in its earliest epochs. Her presentation, “The Many Colors of Galaxies: YOU Can Help NASA Decode the Cosmos,” traces how astronomers read a galaxy’s history from the pattern of colors in its light, and how curious members of the public—no telescope required—are now helping make those discoveries possible.
Coffin begins by placing galaxies on a cosmic timeline that runs from the Big Bang, through the “Dark Ages” when neutral hydrogen blocked all starlight, to the “Cosmic Dawn” when the first galaxies flickered into view, and on to the present day. To locate a galaxy on that timeline, astronomers need its distance—and to find distance, they turn to spectroscopy. She walks the audience through how a spectrograph spreads a galaxy’s light into a spectrum much as a prism spreads sunlight into a rainbow, and how the resulting pattern of bright and dark lines serves as a fingerprint of the elements present. The key measurement is redshift: as the universe expands, light from distant galaxies is stretched toward longer wavelengths—the same effect that lowers the pitch of a siren as it speeds away—and the size of that stretch reveals how far away, and how far back in time, a galaxy lies. The challenge is scale. In a single two-square-degree patch of sky known as the COSMOS field, her team has cataloged roughly 1.8 million galaxies and collected over a quarter-million spectra—far more than any research group can work through on its own.
That is where citizen science comes in. Through Redshift Wrangler, the NASA-funded project Coffin designed and leads as part of her doctoral work, anyone with a computer and an internet connection can take part. Hosted on the Zooniverse platform, the project asks volunteers to box the spectral features in real galaxy data; a clustering algorithm then combines everyone’s markings into a consensus measurement, which Coffin uses to identify line patterns—such as the hydrogen and oxygen emission lines—and calculate each galaxy’s redshift. Since launching in May 2023, Redshift Wrangler has drawn thousands of volunteers, who have contributed over 400,000 classifications across more than 11,000 galaxies. Comparing those volunteer-derived redshifts against an expert catalog, Coffin has found that well-marked spectra hold up remarkably well against professional measurements—a result she stresses depends heavily on the training and support volunteers receive. For her, that community is the point: participants have taken on roles in data analysis, training, and outreach, and the most dedicated have contributed enough to earn authorship on forthcoming publications.
Sadie Coffin is a fifth-year PhD candidate in Astrophysical Sciences and Technology at RIT, where she works with Dr. Jeyhan Kartaltepe on galaxy evolution. A recipient of NASA’s Future Investigators in Earth and Space Science and Technology (FINESST) award for her work using citizen science to identify galaxy pairs, and a former NASA/AAS Citizen Science Leaders Series Fellow, she is also a devoted science communicator who hosts the Rochester chapter of Astronomy on Tap and leads outreach wherever she can. “Projects like Redshift Wrangler prove that big-science discoveries don’t have to stay locked away in academic labs,” she says. “By collaborating with volunteers to analyze galaxy light, we are making astronomical research more open and accessible.”
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