Science & Technology

You've Never Seen a Picture of the Entire Milky Way

Search the internet for pictures of the Milky Way — our home galaxy — and you'll find all sorts of images: bright smudges across the night sky taken by high-end cameras, a horizontal streak taken by powerful telescopes, and an entire spiral galaxy taken by — wait a second. If we live inside of the Milky Way, how do we have pictures of the entire Milky Way? Spoiler alert: we don't. Not real ones, anyway.

This isn't the Milky Way. It's actually NGC 4414, a typical spiral galaxy in the constellation Coma Berenices that's about 55,000 light-years in diameter and approximately 60 million light-years from Earth.

That's Here, That's Home

Earth is located in the Milky Way, but it's nowhere near the middle. We're about 25,000 light-years from the supermassive black hole at the center, and also 25,000 light-years from the outer edge. As Matt Williams writes for Universe Today, if the Milky Way were a vinyl record, we'd be in the groove halfway between the center and the edge. The galaxy itself is shaped like a disc, with a bulge in the center and some warping thanks to the pull of the galaxies nearby.

If you head for an area mostly free of light pollution, like a Dark Sky Park, you can gaze up at and see a faint glowing band streak across the night sky. That's the cross-section of the Milky Way we can see from our vantage point on Earth. (To return to the metaphor, if you were sitting on the outer edge of a vinyl record, you would see it as a flat line, not a circle. Same goes for our galaxy.)

The Milky Way from the International Space Station

But that's from ground level. What about from a spacecraft?

So Close and So Far

The spacecraft that has traveled the farthest from Earth is Voyager 1. On the 40th anniversary of its launch in 2017, the craft was 13 billion miles (21 billion kilometers) away. To put that in perspective, one light-year is about 5.9 trillion miles (9.5 trillion kilometers), and our region of the Milky Way is 1,000 light-years thick. It's safe to say we're not going to leave our galaxy in your lifetime.

But that's not to say we don't have some awesome pictures of what we can see — and even some dependably accurate artist's renderings of what we can't. Powerful telescopes like Hubble, Chandra, and Spitzer (and soon, James Webb) capture images of our galaxy in many different light wavelengths, which astronomers piece back together so they can see past the gas and dust as far into the center as possible. And those same telescopes can see other galaxies in their entirety, gathering data that artists use to inform their estimations of what our galaxy actually looks like.

In that way, the images you've seen of the Milky Way are a lot like the ones you've seen of living dinosaurs. No one has seen either with their own eyes, but decades of research has enabled us to make a pretty accurate guess of what they look like.

Want some drool-worthy space images? Check out "Hubble's Universe: Greatest Discoveries and Latest Images" by Terence Dickinson. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity gets a share of the sale.

Written by Ashley Hamer February 21, 2018

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