A parsec is an astronomical measure of length that stands for "parallax arc-second". It is based on the Earth method of measuring interstellar distances using trigonometry. A star located one parsec away from an observer would have a "parallax angle" of one arc-second.
Based on this, one parsec is exactly equal to 360 × 60 × 60 / 2π AU (206,264.8 AU or ~3.26 light years).
Comparative list of lengths
Each of the following gives a conversion to IAU light years, with appropriate use of significant digits.
- The USS Enterprise-D was 2.2 milliparsecs from the USS Lantree. There were no other vessels within two parsecs of there. (TNG: "Unnatural Selection")
2.2 milliparsecs ≈ 0.0072 light years, or 455.326 AU.
- The USS Enterprise was one-sixteenth of a parsec from 892-IV when it identified the SS Beagle debris. (TOS: "Bread and Circuses")
1/16 parsec ≈ 0.2 light years.
- The Enterprise used sensors to scan a one-half parsec radius, then increased to a one parsec radius. (TOS: "The Enterprise Incident")
0.5 parsec ≈ 1.6 light years.
- The Enterprise-D was supposedly thrown 0.54 parsecs from their position near the Paxans' homeworld. (TNG: "Clues")
0.54 parsecs ≈ 1.76 light years.
- The Enterprise was to pass one parsec from a Klingon outpost. Pavel Chekov thought this was "close enough to smell them." (TOS: "The Trouble with Tribbles")
- The Varro generational ship passed within one parsec of the Natori system more than two months before encountering the USS Voyager. (VOY: "The Disease")
1 parsec ≈ 3.2 light years.
- According to Data's reading of inertial guidance, the Enterprise-D traveled 1.4 parsecs in Nagilum's void without finding any sign of an exit. (TNG: "Where Silence Has Lease")
1.4 parsecs ≈ 4.6 light years.
- Zalkon was 2.3 parsecs distant from where the Zalkonian warship met the Enterprise-D. (TNG: "Transfigurations")
2.3 parsecs ≈ 7.5 light years.
- When the interphase began, the Enterprise was thrown 2.72 parsecs from where the Tholians' field captured them. (TOS: "The Tholian Web")
2.72 parsecs ≈ 8.87 light years.
- When Tom Paris broke the warp 10 barrier, Harry Kim was unable to locate his shuttlecraft on sensors within 5 parsecs of the USS Voyager's position. (VOY: "Threshold")
5 parsecs ≈ 16.308 light years.
- The regions of space known as 2279 PL and 2466 PM are both located approximately 22.3 parsecs beyond Cestus III and the Federation's chart limits during the late 23rd century. (TOS: "Arena")
22.3 parsecs ≈ 72.7 light years.
- The Vega Nine probe traveled 23 parsecs beyond the borders of the Federation, as well as any manned expeditions, to explore the Beta Stromgren system. (TNG: "Tin Man")
23 parsecs ≈ 75 light years.
- All Starfleet units and personnel were evacuated from an area covering 100 parsecs from the planet where Lazarus was found. (TOS: "The Alternative Factor")
100 parsecs ≈ 326 light years.
- The unexplored region where the Metrons stopped the Enterprise and the Gorn ship occupied 1,000 cubic parsecs. The Metrons later hurled Enterprise 500 parsecs distant. (TOS: "Arena")
1,000 cubic parsecs ≈ 34.7 thousand cubic light years.
500 parsecs ≈ 1.63 thousand light years.
- At 98% of its pre-temporal flux strength, the Krenim Imperium spanned 5,000 parsecs of the Delta Quadrant. (VOY: "Year of Hell")
5,000 parsecs ≈ 16.308 thousand light years.
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A parsec is more exactly defined than a light year, since the length of the latter is dependent on the length of the year being used. For example, the IAU uses a Julian year of 365.25 days, while other sources may use a Gregorian year of 365.2425 days, or even some other definition of year.