c in different units
| c (exact) | 299 792 458 m/s |
|---|---|
| km/s | 299 792.458 |
| mi/s | 186 282.397 |
| m/ns | 0.2998 (≈ 1 foot / ns) |
| Light year | 9.461 × 10¹⁵ m ≈ 5.879 × 10¹² mi |
| 1 AU travel time | 499.0 s (8 min 19 s) |
One-way travel times
| From → To | Distance | Time |
|---|---|---|
| Earth ↔ Moon | 384 400 km | 1.28 s |
| Earth → Sun | 149.6 × 10⁶ km | 8 min 19 s |
| Earth → Mars (min) | 54.6 × 10⁶ km | 3 min 2 s |
| Earth → Mars (max) | 401 × 10⁶ km | 22 min 18 s |
| Earth → Jupiter (avg) | 778 × 10⁶ km | 43 min 15 s |
| Sun → Alpha Centauri | 4.24 ly | 4.24 years |
| Milky Way diameter | ~100 000 ly | 100 000 years |
In media (velocity factor)
| Medium | VF | Speed |
|---|---|---|
| Vacuum | 1.0 | 299 792 458 m/s |
| Air (STP) | 0.9997 | ≈ c |
| Glass (n=1.5) | 0.67 | 200 000 km/s |
| Optical fiber | 0.67 | 200 000 km/s |
| Water | 0.75 | 225 000 km/s |
| Coax (typical RG-58) | 0.66 | 198 000 km/s |
| Coax (RG-8) | 0.84 | 252 000 km/s |
| PCB microstrip (FR-4) | ~0.5 | ~150 000 km/s |
Notes
- In vacuum, 1 light-nanosecond ≈ 30 cm (~1 foot).
- In a typical PCB trace on FR-4, signal takes ~150 ps per inch — used for length matching calculations.
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