• Some Figures and Formulas

  The distance between two systems may be calculated by the 3D coordinates (x, y and z) of the two systems with the following formula :
  Distance=square root of [(x1-x2)²+(y1-y2)²+(z1-z2)²]

  Lightspeed is about 300,000 km/second, or 7 AU/hour or 1,000,000,000 km/hour

  1 Parsec equals about 3.2 Light Years.
  1 Light Year equals about 63,000 Astronomical Units (AU).
  1 AU equals about 150 millions kms.
  Distance Earth-Moon is about 385,000 kms.
  Earth's diameter is about 12,800 kms and radius is about 6,400 kms.

• Density of Stars

  The number of stars in a 50x50x50 light years area (a standard administrative district) may vary. In sparse areas roll 2D10, in normal areas roll 2D10x2, and in dense areas, roll 2D10x5.

• Alternate Orbits Calculation

  The first orbit is (1D6) x 0.1 AU.
  Thereafter, multiply each preceeding orbit by [((1D6)x0.1)+1.4] to get the new one. Round result to one or two figures.

• Size of planets and moons

  The diameter may be calculated as follows :
  Tiny Moon: (2D6) x 20kms
  Sub-Terran: (2D6) x 200kms
  Terran: (2D6) x 2000kms
  Super-Terran: (2D6) x 4000kms
  Gas Giant: (2D6) x 40000kms

• Planet Orbital Period

  You can calculate the length of the year (and therefore the length of the seasons - see below Temperature). The calculation is made in Earth's years.
  Take the distance of the planet from the Star (the orbit number, in AU), and add the following modifiers :
  Star O=-50%, Star B=-25%, StarA=-10%, Star F=+0, Star G=+10%, Star K=+25%, Star M=+50%
  The result is the duration of the orbital period in Earth's years (i.e 365.25 days).

• Distance Planet-Moon

  The distance of each moon from its planet may be calculated as follows :
  (1D6) x (1D6) x (1D6)
  The result is the distance in planet's diameters.
  If a result gives an already occupied orbit, add 1D6 until you find an empty orbit number.
  For rings, if you want more realism, just roll 1D6 for its orbit, as they are generally close to the planet.

• Moon Orbital Period

  You can calculate the length of orbital period of the moons around the planet. The calculation is made in Earth's days.
  Take the distance of the moon from the planet (in planet's diameters, see above), and add the following modifiers deduced from planet's gravity :
  Gravity G0=-50%, Gravity G1=-25%, Gravity G2 =-10%, Gravity G3=+10%, Gravity G4=+25%, Gravity G5=+50%
  The result is the duration of the orbital period in Earth's days (i.e 24 hours, not that planet's days).

• Rotational Period

  The rotational period of a planet or moon may be calculated by rolling 3D6 (add 3 for a moon) and consulting the following table :
  3=Fixed
  4=1D6 hours
  5=2D6 hours
  6=3D6 hours
  7=4D6 hours
  8=5D6 hours
  9=3D6x2 hours
  10=3D6x2 hours
  11=3D6x3 hours
  12=3D6x3 hours
  13=3D6x5 hours
  14=1D6 days
  15=2D6 days
  16=5D6 days
  17=3D6x5 days
  18 or more=Fixed
  
  The result is expressed in Earth's hours or days. If the axial tilt of the planet (see below if you want to calculate it) is low, half this time is day and half this time is night. If the axial tilt is not low, the duration of day and night is not equal according to the seasons, and such difference increases for points far from equator, the extreme differences being at each pole.
  For a planet, a "Fixed" result means that the same face is always exposed to the sun. Even if the planet falls into the temperate zone of the Star, only the twilight zone may be colonized, as the hidden side has minimal temperature (H0 or H1), while the exposed side has very high temperature (H4 or H5).
  For a moon, a "Fixed" result means only that the same face is always exposed to the planet (as per Earth's Moon).
  It is also possible to take into account the gravity of the planet : multiply by 2 the Rotation if the gravity is G0 or G1, and divide by 2 if the gravity is G4 or G5.

• Axial Tilt

  This may be calculated as follows :
  (2D6-2)x(2D6-2) degrees
  The result is the axial tilt in degrees. The higher it is, the more differences there are between the seasons (see below Temperature). Any result inferior to 0 shall be zero (no seasonal variations) and any result above 90 must be considered as 90 (extreme seasonal changes).

• Temperatures

  The average temperature on Earth is 15° Celsius. The human metabolism may hardly survive without protection for long period below -50° and above 50°.
  If you want to calculate the average temperature of your temperate planet (the temperature of hot or cold one are too extreme to be calculated this way), you may start at a 15° Celsius and add the following modifiers:
  Star O=+20, Star B=+15, StarA=+10, Star F=+0, Star G=-10, Star K=-15, Star M=-20
  Planet's orbit in inner zone=+10, in middle zone=+0, in outer zone=-10.
  
  The temperature of the planet may vary depending on the latitudes.
  After having assigned (or calculated) an average temperature for the planet, we may calculate the variations at various points on the planet and at various periods of the year.
  The average temperature is the one in temperate latitudes, at Spring or Fall. For the other latitudes, add (diameter/1000) for equator/tropics, remove (diameter/500) for arctic zones.
  To take into account the seasonal effects : For arctic zone, substract the axial tilt in winter and add half of it in summer. For temperate zone, substract half the axial tilt in winter and add quarter of it in summer. No major seasonal change in temperature for equator/tropics.
  For day/night effects, as an average, the temperature decreases by 1° Celsius each hour of night, and increases by 0.5° Celsius each hour of day. Double those figures if the pressure is P0 or P1, and divide them by 2 if the pressure is P4 or P5.
  For height, reduce temperature by 1° Celsius for each 200m above sea level.

• Atmospheric Composition

  For breathable planets, the atmospheric composition is generally close to Earth's one (mainly N2O2).
  For non breathable atmosphere (non vaccum planets), it is possible to determine the main gas composition. Pick one ore more gas in those available depending on pressure :
  
  For P5, like most of gas giants :
  Hydrogen (H2), Helium (He)
  
  For P4 :
  Methane (CH4), Ammonia (NH3), Water Vapor (H2O), Neon (Ne)
  
  For P3 :
  Nitrogen (N2), Carbon Monoxide (CO), Nitric Oxide (NO), Oxygen (O2), Hydrogen Sulfide (H2S)
  
  For P2 : Argon (Ar), Carbon Dioxide (CO2), Nitrous Oxide (N2O), Nitrogene Dioxide (NO2), Ozone (O3)
  
  For P1 : Sulfur Dioxide (SO2), Sulfur Trioxide (SO3), Chlora (Cl2), Fluor (F2), Krypton (Kr), Xenon (Xe), Other composition (complex mix, radioactive gas,...)

• Planet Density

  A planet's density may be calculated in Earth's Density (Earth=1).
  Generally the density is between 50% to 150% of Earth's density, with extreme going up to 200% and down to 10% (which is generally the range of gas giants and stars).
  

• Planet Mass

  A planet's mass depends on its radius and its density.
  The formula is :
  M=(r*r*r)*D
  where M is the planet's mass, r the planet's radius and D the planet's density, all expressed in Earth ones (Earth=1).

• Planet Gravity

  A planet's gravity depends on its radius and its density.
  The formula is :
  G=M/(r*r)
  where G is the planet's gravity, r the planet's radius and M the planet's mass, all expressed in Earth ones (Earth=1).
  or more simply
  G=r*D
  where G is the planet's gravity, r the planet's radius and D the planet's density, all expressed in Earth ones (Earth=1).

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