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To convert ly to km: multiply by 9.461 × 10¹². To convert ly to parsecs: multiply by 0.3066.
1 ly = 9.4607 × 10¹⁵ m = 63,241 AU = 0.3066 pc ≈ 9.461 trillion km.
For example, 1 Light Year (ly) = 3.065982e-7 Megaparsec (Mpc).
| Light Year (ly) | Megaparsec (Mpc) |
|---|---|
| 0.1 | 3.065982e-8 |
| 0.5 | 1.532991e-7 |
| 1 | 3.065982e-7 |
| 2 | 6.131964e-7 |
| 5 | 0.000001532990893 |
| 10 | 0.000003065981787 |
| 25 | 0.000007664954467 |
| 50 | 0.00001532990893 |
| 100 | 0.00003065981787 |
| 500 | 0.0001532990893 |
| 1000 | 0.0003065981787 |
The light-year is the distance that light travels in one Julian year (365.25 days) in a vacuum, approximately 9.461 × 10¹⁵ meters.
1 ly = 9.4607 × 10¹⁵ m = 63,241 AU = 0.3066 pc ≈ 9.461 trillion km.
To convert ly to km: multiply by 9.461 × 10¹². To convert ly to parsecs: multiply by 0.3066.
Expressing distances to stars: Proxima Centauri ≈ 4.24 ly, Sirius ≈ 8.6 ly, Vega ≈ 25 ly.
When you see a star 100 light-years away, you're seeing it as it was 100 years ago — you're literally looking into the past.
Thinking a light-year is a unit of time — it's a unit of distance! It's how far light travels in one year.
Light speed = ~300,000 km/s. In one year, light covers ~9.46 trillion km. That distance is one light-year.
The megaparsec is equal to one million parsecs, approximately 3.26 million light-years, used for measuring distances between galaxies and in cosmology.
1 Mpc = 10⁶ pc = 3.0857 × 10²² m ≈ 3.262 × 10⁶ light-years.
To convert Mpc to light-years: multiply by 3.262 × 10⁶. To convert Mpc to meters: multiply by 3.0857 × 10²².
Measuring distances to galaxy clusters, Hubble flow calculations, and large-scale structure mapping.
The Andromeda Galaxy is about 0.78 Mpc away. The Virgo Cluster is about 16.5 Mpc distant.
Confusing Mpc with kpc — they differ by a factor of 1,000. kpc = within galaxies, Mpc = between galaxies.
Hubble's constant links distance (Mpc) to recession speed (km/s): the farther away a galaxy is, the faster it recedes.



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