Astronomers cannot see what our Galaxy looks like from inside the disk, so they map its shape by measuring how far stars are, how bright they shine, and how they move. By combining these clues with the distribution of gas and dust, they infer a spiral form with several winding arms. The exact number of spiral arms has been a long‑standing topic of debate as new data refine the model of our Galaxy’s structure.
In the 1950s, radio telescopes mapped giant clouds of gas where new stars form, revealing four main spiral arms. NASA’s Spitzer Space Telescope, which hunts infrared light that can pass through dust, looked at the Galaxy in a different way. In 2008 it was announced that Spitzer had scanned around 110 million stars, yet the infrared view highlighted only two prominent arms in that part of the Galaxy.
Today, a twelve‑year study of massive stars has confirmed that the Milky Way indeed has four spiral arms, aligning with earlier ideas and putting to rest the two‑arm interpretation suggested by infrared surveys. This longer view reconciles the various maps and helps astronomers understand how spiral arms organize where stars are born and how they influence the evolution of the disk.
“The Milky Way is our galactic home. By studying its shape we can understand how other spiral galaxies work. For example, we can find out where in these galaxies stars are born and why,” said Professor Melvin Hoare from the University of Leeds. He is one of the scientists who helped map the Milky Way’s third and fourth spiral arms.
Cool Fact
Our Solar System sits in the Orion Arm, a minor spur between the larger arms. It is not at the center of the Galaxy, nor at its edge. It takes roughly 230 million years for the Sun to orbit the galactic center once. Space Scoop.