One light year (abbreviated ly) was a unit of measurement used for establishing distance from one location to another in space. The length of this unit was standardized by the UFP Standards Measurement Bureau. Other space faring species, such as the Sheliak, had their own unit of distance. (TOS: "Where No Man Has Gone Before"; TNG: "The Ensigns of Command")
Examples
In the Treaty of Armens (2255), it was stipulated, "Third party assistance may be requested from a Federation Starfleet vessel or a Sheliak Corporate spacecraft if the distance from the vessel to the respective homeworld is greater than five thousand (5.0×103) light years. UFP Standards Measurement Bureau Units. Assistance may also be requested if the vessel is less than 1,000 light years from a standard UFP subspace relay booster station." (TNG: "The Ensigns of Command")
When Commander Benjamin Sisko welcomed the first guest from the Gamma Quadrant in the Alpha Quadrant, a Tosk, he told him that he traveled almost ninety thousand light years through the wormhole. (DS9: "Captive Pursuit")
In 2369, a Vanoben transport was raided two light years away from Deep Space 9. (DS9: "Vortex")
The same year, Sisko told Kai Opaka that the Gamma Quadrant is seventy thousand light years away from Bajor. (DS9: "Battle Lines")
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Background information
The light year is the distance that light travels in one Earth year. It is approximately equal to 9.46×1012 kilometers, or 5.88×1012 miles.The exact length of a light year depends on the exact length used for one "Earth year". The IAU uses a Julian year of 365.25 days, while other sources may use a Gregorian year of 365.2425 days, or another year altogether.
| Source | year (days) | light year (kilometers) | light year (miles) |
|---|---|---|---|
| IAU | 365.25 | 9,460,730,472,581 | 5,878,625,373,184 |
| Gregorian | 365.2425 | 9,460,536,207,068 | 5,878,504,662,190 |
| 365.242199 | 9.460 528 4×1012 | 5.878 499 81×1012 | |
| Yahoo | 365.2411‡ | 9.460 5×1012 | 5,878,482,164,161 |
‡ Note that while Yahoo separately reports a year length of 365.24220 days, its rounding of the light year length to five digits works out to a year length of ~365.2411 days.