How Scientists Use Images of the Sky to Time Travel to Stars
It's no secret that I'm a big fan of the American Museum of Natural History's series Shelf Life, which gives viewers a behind-the-scenes look at the museum's collections. This month's episode, "How to Time Travel to a Star," is a little different than previous episodes, because the collections of astrophysicists look a lot different than traditional natural history collections.
"One of the differences between natural history collections and astro collections is that because ours live on hard drives, instead of in cabinets, they take up a whole lot less room," says Ashley Pagnotta, a Davis Scholar at AMNH. These collections are composed of outputs from formulas created by theoretical and computation astrophysicists and, for observational astrophysicists, images of the sky. These days, the images are mostly digital, but more than a century ago, astronomers would snap photos of the sky using glass plates coated with a photo emulsion.
The astronomers would take photos of the sky in a regular, orderly fashion, giving us a good record of what the sky looked like in the past—and, in a way, allowing us to travel back in time to see what the skies looked like then. "We simply have one record of the universe streaming by us,"says Mike Shara, a curator of Astrophysics at the museum who studies exploding stars, "and because astronomers a century or more ago were snapping pictures, we have a continuous record over an enormously long period of time."
Harvard has the largest glass plate collection of astronomical photos, which dates back to 1860, and is working to digitize them. At AMNH, Pagnotta and Shara worked with high school students in the museum's Science Research Mentorship Program (SRMP) to bring catalogs of distances to stars in the Magellanic Clouds around our galaxy—which were created by Henrietta S. Leavitt in the early 1900s and updated by Cecila Payne-Gaposchkin in the 1950s—into the present day. The distances were only accurate for the eras in which they were created, so the students created a computer program that would account for 3D space and the wobbling of the Earth's axis. The data will be published and made available to the scientific community. "Once this catalog is complete—and it's almost finished—we will have a digital, fully accessible catalog that anyone in the world can use," Pagnotta says. "And then from there, you can start to do science—see how these stars change over time. We think that they probably do change over a hundred years, but we don't really know what they do. Nobody's ever looked before."