A new iPhone app lets you find the center Milky Way simply by using your smartphone — and it’s made with ChatGPT.
The free app called Galactic Compass was developed by Matthew Webb and released on the Apple App Store on February 15. It is designed to always point users in the right direction Galactic center, regardless of the position of the Earth in the cosmos. Webb’s inspiration for the app comes from years of teaching himself how to always know where to look for the Galactic Center, which changes as we move through it room. He wrote about the thinking behind the Galactic Compass in post on his personal website, which also announced the release of the app.
“I’d end up pointing my finger through the sidewalk or down the street and think ‘huh, that’s where it is,'” Webb said in the post. “At the end I had this image of myself, and Earthand solar system, and the center of the galaxy that initially revolved around me, and now turned, I revolved around it. It was wildly situated.”
Related: Something strange is happening to the black hole at the center of the Milky Way
The app itself is pretty straightforward: to locate the Galactic Center, open the app and place your iPhone on a flat surface. A large green arrow will then appear pointing in the direction of the Milky Way core, where a supermassive black hole called Sagittarius A* resides. And that’s about it.
Sagittarius A*, or Sgr A* for short, has an estimated mass millions of times that of our sun. While the majority Black holes form from the collapse of the massive stars, Sgr A* is far too massive to have formed from a single star. Instead, a possible explanation is that multiple smaller black holes merged to create this supermassive black hole.
Using a simple application to identify such a puzzling structure in our universe it’s incredibly humbling. It puts into perspective our place in the unimaginable vastness of the cosmos, which is probably not something many people think about often — at least I didn’t before this new app was created.
Now I can easily locate the direction of the core of the Milky Way using a device that is used for almost everything I do during the day. And the simplicity of the app’s interface — a simple green arrow fashioned from an extruded rectangle and a squashed pyramid, Webb says — makes grasping such an inscrutable cosmic structure a little less daunting.
“Back in 2020, Robin Sloan said that an app can be a home-cooked meal,” Webb wrote on his website, noting that it’s enough for a small piece of software to simply meet the needs of its developer. “Now I’ve cooked a meal that anyone with an iPhone can download. Probably only a few dozen people will want it, but I want it in my pocket and I want to share it with my friends, and here we are. And I don’t even know how to cook!”
Webb developed the Galactic Compass interface using the AI tool ChatGPT and integrating complex calculations to locate the Galactic Center relative to the user’s date and location while in the app. This involved a mathematical technique called quaternions, which represents the spatial orientations and rotations of elements in 3D.
Essentially, Webb asked ChatGPT for step-by-step instructions on how to build the app through a series of questions he fed into the chatbot. He then copied and pasted the code from ChatGPT into Xcode, making sure each step was completed before moving on to the next. When he encountered an error, he would ask ChatGPT for a solution and continue piecing together pieces of code to build his Galactic Compass, he explained in his post.
Webb programmed the app so that the 3D arrow rotates in real time in response to the orientation of the device. The phone must be flat in order for the arrow on the screen to orientate correctly pointing towards the direction of the galactic center as a fixed point.
“The Galactic Compass is still pretty inept, for sure,” Webb said in a post on his website. “But it’s not bad for a collaboration between someone who can’t build apps and an AI that’s barely a year old.”