How big is the universe?

1. 1

   Zib says

   Light is the fastest thing there is, so we measure space in light-years: how far light goes in a year. The nearest star past the sun is about four light-years away. Our galaxy, the Milky Way, is about 100,000 light-years across. The part we can see stretches about 92 billion light-years across, with hundreds of billions of galaxies.

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2. 2

   What's beyond the part we can see?

   The farthest galaxies we've spotted sent their light out about 13.5 billion years ago. That light has been travelling ever since, and it's only just reaching our telescopes. Scientists are pretty sure the universe carries on well past what we can see. Nobody knows yet if it ever ends.

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3. 3

   So how can the part we see be 92 billion light-years across?

   The universe is stretching, so galaxies keep drifting farther apart. While that old light was on its way to us, the galaxies that sent it kept moving off. Now they're much farther away than when the light left. Measure to where they are today, in every direction, and you get about 92 billion light-years across.

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In Lil' Phil, reaching the bottom of this wonder earns a sticker for Zib's collection.

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