Interplanetary Positions

The following is a sidebar found on page 109 of Starships (Traveller GURPS). It has not (yet) been modified to Star Trek terms.

How Far Is That Gas Giant?

Computing travel time between planets is simple, once you know the distance between them (see p. GT119). The only problem is that in a planetary system everything is constantly moving; the distance to the gas giant will be different next month. One way to determine relative planetary position is to assume that on 001-0000 all the planets in every star system were lined up. To determine the distance between planets, follow these steps:

1. Divide the day number by 365, add the year number, and then divide the sum by the planet's period (in years). Keep only the decimal pan of the answer. Multiply this by 360" to find the planet's orbital location. This is value X.
2. Repeat step one for the other planet. This is value Y.
3. Subtract X from Y to find the angle between the planets. This is value Z.
4. Compute the distance between the planets using this formula: square root (A x A + B x B - 2 x A x B x cos(Z) where "A" is the orbital radius of the first planet and "B" is the orbital radius of the second planet