By the numbers
93 billionlight-years across (observable)
13.8 billionyears since the Big Bang
100s of billionsof galaxies, perhaps trillions
8 minfor sunlight to reach Earth
A light-year is the distance light travels in a year, about 5.9 trillion miles.
Looking out is looking back
- The MoonLight left it about 1.3 seconds ago
- The SunAbout 8 minutes ago
- The nearest starJust over 4 years ago
- The farthest galaxiesMore than 13 billion years ago
Why 93, not 27?
Space itself has stretched while the light was traveling, so the most distant galaxies are now much farther away than when the light left.
Our cosmic address
| Place | Size |
|---|---|
| Earth | About 8,000 miles wide |
| Solar system to Neptune | About 2.8 billion miles from the Sun |
| Milky Way | About 100,000 light-years across, 100–400 billion stars |
| Observable universe | About 93 billion light-years across |
Beyond the observable edge there is almost certainly more universe; its light hasn't reached us.
Sources: NASA; European Space Agency
Remember
Every time you look up at night, you are seeing the past, and the universe is far bigger than what we can see.
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Answer key
- About how wide is the observable universe?93 billion light-yearsExpansion makes it about 93 billion light-years across.
- How old is the universe?13.8 billion yearsThe Big Bang was about 13.8 billion years ago.
- What is a light-year?The distance light travels in a yearIt's a distance, about 5.9 trillion miles.
- How long does sunlight take to reach Earth?About 8 minutesAbout 8 minutes and 20 seconds.
- Why is the observable universe wider than 13.8 billion light-years in each direction?Space has expanded while light traveledDistant galaxies have been carried farther away by expanding space.