Textbook views of the Milky Way show a long bar of stars in the middle, with several spiral arms wrapping around it. But that picture is incomplete. And some of it might not be right. In fact, astronomers are still trying to develop a complete and accurate diagram of our home galaxy.
The problem is that they’re trying to map the Milky Way from the inside. It’s like trying to map a million square miles of forest from a single spot deep inside it. Not only can you not see the rest of the forest, you don’t even know how far it extends.
Astronomers began trying to map the Milky Way a few centuries ago. In the late 1700s, for example, William Herschel counted all the stars he could see through his telescope and used their brightnesses to plot their distances. But giant clouds of dust permeate the galaxy. They absorb the light of the stars behind them, making them invisible — hiding large swaths of the Milky Way’s structure.
In the 20th century, astronomers began using radio telescopes to measure clouds of gas, which are abundant in the spiral arms. Radio waves penetrate the dust, so they made it possible to map the galaxy’s overall layout.
Today, new radio surveys provide ever more detailed views of the Milky Way. And astronomers haven’t given up on counting stars. The Gaia spacecraft has mapped more than a billion stars. That provides details on the structure of some of the galaxy — part of the ongoing effort to map our galactic home.
Script by Damond Benningfield