Astronomy
Travel time at a fraction of light speed
Distance in light years divided by the fraction of light speed gives the trip time in years, because a light year is one year of light travel.
The Formula
t = d / f
Distance in light years divided by the fraction of light speed gives the trip time in years, because a light year is one year of light travel.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| d | Distance | light years | In light years. |
| f | Speed fraction | dimensionless | Spacecraft speed as a fraction of light speed, between 0 and 1. |
| t | Trip time | years | Coordinate time in years, ignoring relativistic effects. |
What Each Symbol Means
dlight years
Distance
In light years.
fdimensionless
Speed fraction
Spacecraft speed as a fraction of light speed, between 0 and 1.
tyears
Trip time
Coordinate time in years, ignoring relativistic effects.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate light years page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Light Years, filed under Science. Every number the guide produces comes from substituting into this one line.