At some point as children, many people learn to identify one or two star patterns: The Big Dipper, Scorpius, Orion’s Belt. As adults, they see those same shapes again, the star patterns seeming distant and eternal. So it’s easy to forget that the seemingly immutable shapes in the sky are, in fact, always changing. Stars haven’t always been in the position in the sky as they are now, nor will they be in that position forever.

At a recent hackathon at the American Museum of Natural History, one team made an app to remind us of that fact. Using Space Time, users can travel forward and back in time (using a little Delorian slider) to see how the stars, and their corresponding constellations, transform throughout the years.

Here’s hacker Robby Kraft demonstrating how the app works:

Not only does Space Time reveal that in the 1800s B.C., when the Babylonians were first developing the star charts that the Greeks later adopted and passed down to us, the stars were in slightly different places. And when anatomically modern humans arose in the form of Homo sapiens 200,000 years ago, the stars were in vastly different places. Should we humans manage to not destroy ourselves in the coming 200,000 years, our ancestors will look up into the sky and see not a scorpion and a bear, but a totally different arrangement of stars. The constellations we see today (which already, if we’re honest, don’t actually look like bears or scorpions or any of those things) will be even harder to identify.

Jana Grcevich, a post-doctoral researcher in astrophysics at the museum who worked with the team to develop the app, says that the projections have some limitations. “Each star has a complicated orbit within our galaxy that we're approximating as a straight line through space from the perspective of a viewer on earth,” Grcevich told me in an email. “Many stars don't orbit nicely around the center of galaxy in an ellipse, some have crazy spirograph orbits that take them out of the plane and alter how far they are from the center of the galaxy.” And the app shows the stars moving on a single plane, but in reality they’re actually moving in three dimensions. And, of course, the way people see stars when they simply look up isn’t quite the same as what astronomers see when they look through their telescopes.

All that said, Grcevich still thinks the app is showing interesting and useful data. “Despite all my caveats, you can definitely get a sense for how the constellations will change shape over time with the app,” she said, “and I think ancient Egyptians or even the first modern humans could recognize the sky we plot, if you taught them to use a computer.”

The team hopes to release their app to the iTunes store soon.