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Why looking at space is like looking back in time

Light from the center of the Milky Way takes 25,000 years to reach Earth.

The galaxy we call home is unfathomably enormous. With enough room for an estimated 100 billion planets, the Milky Way stretches about 100,000 light-years across, although estimates of its full size vary. (A light-year is the distance a beam of light travels in one year on Earth, equal to about 6 trillion miles.) Earth is situated approximately two-thirds of the way from our galaxy’s center; we’re essentially in the suburbia of the Milky Way. When we look at celestial bodies, we’re actually looking back in time, because of how far away they are and how long their light takes to reach us. The sun we see, for example, is always about8.3 minutes old, while the light from the North Star, aka Polaris, is about 320 years old. And while we can’t actually see the center of the Milky Way, light from the area takes nearly25,000 years to reach our planet. That means it dates back to when humans were still in the Stone Age. 

What we know about our galaxy is ever-expanding — much like the universe itself. Early astronomy pioneers such as Aristotle believed the Earth was the center of the universe, circled by the sun, moon, and all other cosmic matter. In 1609, Galileo’s first glimpse of the Milky Way through an improvised telescope showed its wispy appearance wasn’t a layer of clouds, as previously thought, but a vast collection of individual stars. His discoveries lent credence to the idea that Earth wasn’t the center of the universe after all. Yet it would take 300 more years for scientists to confirm that we’re not even at the center of our own galaxy — it wasn’t until 1924 that astronomer Edwin Hubble confirmed that the Milky Way is just one of many galaxies in our vast universe. 

Numbers Don’t Lie

Age (in years) of the Milky Way galaxy

13.6 billion

Year the Hubble Telescope was launched into space


Estimated number of galaxies in the universe

2 trillion

Suspected number of planets within 50 light-years of Earth



The Milky Way goes by different names around the world.

The Milky Way is best known by that name, likely thanks to the Greeks, but stargazers elsewhere have used a variety of monikers for the band of stars and dust we call home. The galaxy is called the “Silver River” in China and Vietnam, “Backbone of the Night” in the Kalahari Desert of Southern Africa, and “Winter Way” in the Faroe Islands and some Nordic countries. Regardless of what name you use, the Milky Way is observable from nearly any place on Earth, so long as you find a spot fairlyfree of light pollution. Interstellar medium (aka space dust and gas) can make it tricky to observe significant detail without a telescope, but it's still possible to see a spectacular cosmic show without any magnification.

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