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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) = 1.787813e+26 Bohr Radius (a₀).
| Light Year (ly) | Bohr Radius (a₀) |
|---|---|
| 0.1 | 1.787813e+25 |
| 0.5 | 8.939066e+25 |
| 1 | 1.787813e+26 |
| 2 | 3.575626e+26 |
| 5 | 8.939066e+26 |
| 10 | 1.787813e+27 |
| 25 | 4.469533e+27 |
| 50 | 8.939066e+27 |
| 100 | 1.787813e+28 |
| 500 | 8.939066e+28 |
| 1000 | 1.787813e+29 |
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 Bohr radius is the most probable distance between the nucleus and the electron in a ground-state hydrogen atom, approximately 5.292 × 10⁻¹¹ meters.
a₀ = ℏ/(mec α) = 4πε₀ℏ²/(mee²) ≈ 5.29177 × 10⁻¹¹ m, where α is the fine-structure constant.
To convert Bohr radii to meters: multiply by 5.29177210903 × 10⁻¹¹.
Sets the characteristic scale for atomic sizes. Most atoms have radii of 1–3 Bohr radii.
The Bohr radius gives atoms their characteristic size of ~1 Å (10⁻¹⁰ m), explaining why matter has the volume it does.
Confusing Bohr radius with atomic radius — the Bohr radius is specific to hydrogen; other atoms have different sizes.
The Bohr radius tells you 'how big atoms are' — about 0.5 angstroms. It's the atomic analog of a ruler for atomic-scale physics.



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