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Astrography is the science of mapping interstellar space.

  • Sometimes Astrography is mistaken for the related science of Astrogation.


Astrography is the art and science of mapping out interstellar space. An astrographer is someone who maps out interstellar space.
Astrogation is the actual planning of the navigation of spacecraft. Or the planning of a route through space, either in interplanetary or interstellar travel. An astrogator is someone who navigates a spacecraft, or starship, through interstellar space.

Please see the following AAB articles for related information:

Description (Specifications)[edit]

Basic to any science of mapping is a coordinate system. The scientific system used by the Imperium is based on rings of longitude, rays of latitude, and parsecs. By convention, rays of latitude and rings of longitude are measured from a starting point at Reference (Core 0140), the world where the data from the First and Second Imperial Grand Surveys are stored.

  • The concentric ring passing through Reference/Capital is labeled the 10,000th ring, and is used as a baseline. Similarly, the ray of latitude extending from the center of the Galaxy through Reference/Capital is designated as the first ray. Measurement is in parsecs, counting in the trailing direction. Computation reveals that the circumference of the 10,000th ring (r=10,000) is 62,832 parsecs. Counting spinward uses a subtraction from 62,833, which is the equivalent of the zero baseline.
  • For example, Regina, of the Regina Subsector, in the Spinward Marches, is 9930 ring/ray 62723.
    • The format for expression of location is xxxx ring/ray yyyyy, where xxxx is the ring of longitude (distance from the galactic core in parsecs), and yyyyy is the distance of the ray of latitude (in parsecs) from the first ray of latitude, measured along the ring of longitude in the trailing direction.

Galactic Four Prime Directions[edit]

The four prime Astrographic directions are:

Please see Galactic Directions for more information.

Stellar System Topography[edit]

The following terms are in common use to describe locations within a Star System:

Units of Imperial Socioastrographic Measure Measure[edit]

Please see to learn more about Imperial astrographic organization:

  • Charted Space, or Known Space (all charted sectors)
  • Domain (4 sectors)
  • Quadrant (1/4 of a sector or 4 subsectors)
  • Sector (1 sector) (Called a province by the Zhodani)
  • Subsector (1/16 sector) (Also called districts)
  • County (Less than 1/16 of a sector) (Usually a multi-world planet grouping)
  • World (Less than 1/16 of a sector) (A single planet)

Imperial Astrographic Measurement Data Table[edit]

The following terms for astrographic measurement are in widespread use throughout Imperial Charted Space:

Term Sector
Charted Space All known
All known
All of charted space is still but a fraction of the known galaxy.
  • Sometimes informally referred to as "known space".
Domain 4 64 Domains often include attached nearby territories in their realm of control.
  • Many domains don't include complete (100%) control of the entire domain.
  • Occasionally known as "demesnes".
Sector 1 16 Also known as "marches", "matrixes", "provinces", "reaches", and "regions" among other titles.
Quadrant 1/4 4 Sometimes confusingly used to refer to a whole Sector rather than several (four) subsectors.
  • In some antiquated pre-Imperial measurement systems, four sectors formed a super-sector composed of four sectors each called quadrants.
Subsector 1/16 1 Sometimes referred to as "Districts".
  • A County is a political measurement that may be smaller or larger than a subsector.
World Fraction Fraction A single world, overseen in the Third Imperium by an Imperial noble of the rank Marquis or above.
  • Groupings of nearby worlds are called clusters.

History & Background (Dossier)[edit]

Imperial Science: This mapping system is highly Imperio-centric, and other systems are used by other peoples and races outside the Imperium. This system has gained wide acceptance, however, among Imperium dominated client-states, human and otherwise. This mapping system breaks down and is prone to error beyond certain limits. It does serve admirably for a band approximately 400 parsecs wide at a longitude of 10,000 parsecs, which is a region precisely centered on the Imperium.

In ordinary discourse, a world is referred to by its name then sector and parsec/hex in parentheses. For example, the homeworld of Archduke Norris is Regina (Spinward Marches 1910): That is, the world Regina is in hex 1910 in Spinward Marches Sector.

  • When specifying the location of sectors, a coordinate system is used with Core sector being at (0, 0).
  • Thus the Spinward Marches would be at (-4, 1) and the Reavers' Deep would be at (-2, -2).
  • This can be better viewed on the Charted Space map.

Astrographic Distances Data Table[edit]

Some of the most common units of measure for interstellar distances include:

# Base Unit Astronomical unit
(Imperial Standard)
1. Parsec (pc) 206,260 AU 3.2637 ly
170.069 lw
1190.484 ld
28,571.616 lh
1.714×106 lm
102.858×106 ls
1.0 pc 30.856 trillion km 19.173 trillion miles
2. Light-year (ly) 063,200 AU 1.0000000 ly
52.143 lw
365.00 ld
8760.00 lh
525,600.00 lm
31.536×106 ls
0.3064 pc 9.454 trillion km 5.875 trillion miles
3. Light-week (lw) 001,212.055 AU 0.0192 ly
1.0 lw
7.0 ld
168.0 lh
10,800 lm
604,800 ls
5.876×10-3 pc 181,314 million km 112,630 million miles
4. Light-day (ld) 000,173.151 AU 2.738×10-3 ly
0.143 lw
1.0 ld
24.0 lh
1440 lm
86,400 ls
8.395×10-4 pc 25.902 billion km 16.094 billion miles
5. Light-hour (lh) 000,007.215 AU 1.1408×10-4 ly
5.9524×10-3 lw
0.0417 ld
1.0 lh
60.0 lm
3600.0 ls
3.498×10-5 pc 1.079 billion km 670.6 million miles
6. Astronomical unit (AU) 000,001.0000 AU 1.581×10-5 ly
0.0008 lw
0.0058 ld
0.1387 lh
8.3195 lm
499.1681 ls
4.848×10-6 pc 150 million km 93 million miles
7. Light-minute (lm) 000,000.1202 AU 1.901×10-6 ly
9.941×10-5 lw
6.944×10-4 ld
0.017 lh
1.0 lm
60.0 ls
5.830×10-7 pc 17.99×106 km 11.18×106 miles
8. Light-second (ls) 000,000.0020 AU 3.1688×10-8 ly
1.6534×10-6 lw
1.1574×10-5 ld
0.0003 lh
0.0167 lm
1.0 ls
9.7159×10-9 pc 299,792.458 km 186,282.397 miles
9. Mile (mi) Fraction Fraction Fraction 1.609344 km 1.000000 mile
10. Kilometer (km) Fraction Fraction Fraction 1.000000 km 0.621371 mile

Common Imperial Chronology[edit]

Some of the most common units of measure for chronography (time measurement) include:


  • A Standard Imperial Day is exactly 24.00 hrs long, by definition.
  • A Standard Imperial Year is exactly 365 standard days long, by definition.

  • A Terran Local (Solar) Day is exactly 24.00 hrs long, by definition (1.0000 standard days)..
  • A Terran Rotational Period is 23h 56m 4s long (0.9973 standard days).
  • A Terran Orbital Period (Year) is is 365.2564 standard days in length (1.0007 standard Imperial years).

  • A Vlandian Local Day ("Drandir") is about 31.8 hours long.
  • A Vlandian Rotational Period is 31h 48m 18s long (1.3252 standard days).
  • A Vlandian Orbital Period (Year) ("Gurkula") is 478.72 standard days in length (1.3116 standard Imperial years), or 360 drandir.

  • A Sylean Local Day ("unknown") is about 24.06 hours long.
  • A Sylean Rotational Period is 24h 4m 1s long (1.0669 standard days).
  • A Sylean Orbital Period (Year) is 364.97 standard days in length (0.9999 standard Imperial years).

Astrographic Branches[edit]

References & Contributors / Sources[edit]

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