Distance → delay
1 km takes light about 3.34 µs
The calculation uses the exact SI value c = 299,792,458 m/s in vacuum.
Light time3.34 µs
Light-travel time3.34 µs0.000003 seconds
Distance in meters1,000 mtime = distance ÷ c
Exact constant, approximate astronomy
What the number means
The speed of light in vacuum is exactly 299,792,458 m/s because the SI metre is defined using that fixed value. Real astronomical distances change continuously, so Earth–Moon and Earth–Sun presets are representative average distances rather than a live ephemeris.