In 1994, a major earthquake struck California and triggered a blackout across Los Angeles. Afraid to stay indoors, people walked outside and looked up. They couldn't believe their eyes.
A local observatory reported that several residents called in, alarmed.
"Sir, please tell me—that silvery band stretching across the sky. Is it some kind of sign? A bad omen?"
The astronomer on duty was amused.
"No, sir. That's the Milky Way. The galaxy where our Sun lives. It's always been there."
Have you ever imagined what the world looked like before electricity?
I'm an astrophysicist. I study the Milky Way—the galaxy that contains our Sun. There's something ironic about my profession. I grew up in Kuala Lumpur, where the night sky is perpetually washed out. Nothing visible. Even when I return to Sibu, where I was born, I can only occasionally glimpse a few of the brightest constellations. When I tell friends back home that I study the night sky, they're often puzzled: "Really? What's out there to study?"
We focus so much on the benefits of technology that we forget the costs.
Technology has given us the splendor of cities. But that splendor has a shadow. Progress moves so fast that we lose perspective—it's hard to remember that electric lighting is barely 150 years old. For most of human history, a brilliant star-filled sky was the norm. Only in the last century has light pollution swallowed the night, blocking out the stars, replacing wonder with an empty orange glow.
As the saying goes, when one door closes, another opens. But today, that new door is much farther away—even if the real starry sky is still out there, somewhere.
Most large telescopes are built in the most remote places on Earth, forcing astronomers like me to make difficult journeys. To travel from my home in Princeton, New Jersey, to an observatory in Chile, I have to take three flights and then drive for hours across the Atacama Desert.
And yet, the moment I arrive and see what the Milky Way truly looks like, every hardship feels worthwhile.
I often wonder: written history goes back only a few thousand years. But for hundreds of thousands of years before that—before writing, before language—how many people sat in caves and stared at this same sky? And how fortunate am I to live in an era when we can finally begin to understand what we're seeing?
Tracing the Footsteps of Stars
Ancient Greek mythology held that the Milky Way was the breast milk of the goddess Hera—hence the name. We now know it's not mythical milk but a vast collection of stars, including our own Sun.
We've long understood that the Sun is not unique. It's an ordinary star, one of roughly a trillion in the Milky Way. That's ten times more stars than all the humans who have ever lived—including every one of your ancestors. And the galaxy's size is equally staggering: about 100,000 light-years from one end to the other.
To put that in perspective: if you shot a beam of light from one edge of the Milky Way, it wouldn't reach the other side for 100,000 years. And remember, that same beam of light can circle Earth seven and a half times in a single second.
How do we know this? While technology stole the night sky from most people, it also gave us new ways to see what was always invisible. In principle, measuring the size and mass of our galaxy shouldn't be too hard. We can't physically reach the Sun, but we can measure how fast the Earth orbits it. That orbital speed tells us the Sun's gravitational pull, which tells us its mass. The same logic applies to the Milky Way: if we can track how stars move, we can infer the galaxy's mass and structure.
The problem is that measuring stellar motion is fiendishly difficult. As a kid, I loved watching planes crawl across the sky. They look slow, but they're actually traveling ten times faster than highway speed limits. The apparent slowness comes from distance—when something is far away, even rapid motion looks tiny. Now imagine trying to measure the motion of stars thousands of light-years away. The challenge is immense.
A Revolutionary Telescope
As Kennedy said: "We choose to go to the Moon not because it is easy, but because it is hard."
To understand the Milky Way, the European Space Agency launched the Gaia telescope in 2013. How precise is Gaia? Imagine detecting the movement of a single human hair from tens of kilometers away. That's the level of resolution we're talking about. Gaia has measured the positions and motions of billions of stars, revolutionizing our understanding of the galaxy.
And Gaia is just the beginning. Many other surveys are collecting different kinds of data about the Milky Way's stars. Our interest goes far beyond simply measuring the galaxy's size. Research on the Milky Way has exploded in recent years, producing discovery after discovery. In future columns, we'll explore some of these findings.
I live in Princeton, not far from New York City. Here, as in most of the world, the Milky Way is invisible. But not seeing it with my own eyes doesn't limit my research. Modern astronomy has long surpassed our five senses—even our imagination.
Our technology has split one sky into two. The first is drowned in light pollution, so dull that most people never think to look up. The second exists beyond ordinary perception, revealed only through instruments. As an astrophysicist, I have the privilege of moving between these two skies.