SPACE ATLASSTUDENT REFERENCE · GRADES 4–8
Universe · Question

Is a light-year a measurement of time or distance?

Despite the word "year," a light-year measures distance: how far light travels in one Earth year, about 9.46 trillion km. Select a light source below to compare its distance and explore how long its light takes to reach Earth.

Visual model

When did that light leave?

Preparing the comparison controls. The Sun reference below is available now.

Eight sources, vastly different distancesLight-years from Earth · logarithmic scale
10^-8 ly 10^-5 ly 10^0 ly 10^5 ly 10^7 ly Moon: approximately 4.12e-8 light-years away Sun: approximately 0.0000158 light-years away Neptune: approximately 0.000468 light-years away Proxima Centauri: approximately 4.25 light-years away Sirius: approximately 8.6 light-years away Polaris: approximately 433 light-years away Milky Way center: approximately 26000 light-years away Andromeda: approximately 2500000 light-years away

Selected on ruler: Sun · ~0.0000158 light-years from Earth

The Moon is near the left; Andromeda is far to the right. Equal horizontal gaps mean equal distance multipliers, not equal kilometres. Choose a source above and watch its mark move.

8.3 minutes

Sunlight takes about 8.3 minutes to reach Earth. This is the starting reference for comparing light-travel distances.

Follow a single light signalScrub through the trip
Sun · light emittedEarth · observer
Travel time elapsed8.3 minutes
Travel time remaining0.0 seconds

At 100%, light from the Sun is arriving at Earth after approximately 8.3 minutes.

The path always fills the width for one selected journey. It is not a distance scale between different objects. Use the logarithmic ruler above for comparing sources. There is no autoplay or simulated measurement; move the slider to explore travel time.

Measurable fact

The distance ladder.

  • 1.3 light-secondsEarth to the Moon
  • 8.3 light-minutesEarth to the Sun (1 AU)
  • ~4.1 light-hoursEarth to Neptune
  • 4.25 light-yearsTo Proxima Centauri, the nearest star to the Sun
  • ~26,000 light-yearsEarth to the center of the Milky Way
  • ~2.5 million light-yearsTo the Andromeda Galaxy, the nearest large galaxy
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Galactic distance

Where are we in the Milky Way?

Apply light-year distances to the location of our Sun and the galactic center.

Find our galactic location ↗