Measuring Distances

A few ‘standard’ units are in use to measure distances in space.

  • light Seconds
    A Light Second (abbreviated as LS) is defined as the distance that light travels in free space in one second, and is equal to exactly 299,792,458 metres.
    • 299,800 km
    • 0.0020039888 AU
  • Light Minutes
    A Light Minute (abbreviated as LM) is defined as the distance that light travels in free space in one minute.
    • 17,987,547.5 km
    • 60 light seconds
    • 0.120239328 AU
  • Astronomical Unit
    An astronomical unit (abbreviated as AU) is a unit of length defined as 149,597,870,700 metres (92,955,807.273 mi) exactly or roughly the mean Earth–Sun distance.
    • 149,597,870.7 km
    • 8.317 light minutes
  • Light Hour
    A Light Hour (abbreviated as LS) is defined as the distance that light travels in free space in one hour.
    • 1,079,252.85 km
    • 60 light minutes
    • 7.21435969 AU
  • Light Day
    A Light Day (abbreviated as LD) is defined as the distance that light travels in free space in one day.
    • 25,902,068,371.2 km
    • 24 light hours
    • 173.144633 AU
  • Light Week
    A Light Week (abbreviated as LW) is defined as the distance that light travels in free space in one week.
    • 181,314,478,598.4 km
    • 7 light days
    • 1212.01242879 AU
  • Light Year
    A light Year (abbreviated as LY) is a unit of length equal to just under 10 million million kilometers (or about 6 million million miles) and the distance that light travels in a vacuum in one Julian year. The light-year is mostly used to express distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications.
    • 9,460,528,400,000 km
    • 60 light hours
    • 63,241.077 AU
  • Parsec
    The parsec (abbreviated as PC) is a unit of length used in astronomy equal to about 30.9 trillion kilometres (19.2 trillion miles). In astronomical terms it is equal to 3.26 light-years. It is derived from a distance corresponding to a parallax of one arc second.
    • 30.9 trillion km
    • 3.26 light years
    • 206,264.8 AU
Distance in Space Combat

Finding ‘small’ objects in space is difficult. The larger and closer an object is the easier it is to find. Which explains why finding asteroids can be very difficult (most are small and far away). Spacecraft can be spotted by travelling in front of other larger objects or by their waste heat from their drives. Most spacecraft exhaust the majority (or all) their heat through their engine exhaust, this minimizes their heat from directions other than aft. Active sensors will also increase range of detection as it increases detection ability in the one using it.

Space combat maximum engagement range is 1 light minute. This is the maximum range for guided weaponry under most conditions. It’s also a maximum range from which most commanders will release fighter craft. A more conventional fighting range is around 1 light second. There are two reasons for that: most direct fire weapons fire in this range, and because of the lag of the speed of light one cannot even tell where an enemy is in something approaching real time at more than 1 light second. Most sensors and weapons work at light speed (or very close to it), so at a range of 10 light seconds it takes 10 seconds for the beam or round to hit (or not) and another 10 seconds for sensors to show the results of an attack.

Measuring Distances

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