Initial Phase Angle of the Mun

[Sovnheim]

Hello all,

I am currently designing an calendar forecasting the position of all KSP celestial bodies vs. Kerbin at a given time in-game.

Therefore what I need first is the initial angle of the body at UT = 0 in game.

Looking on the Wiki, I couldn't manage to find the position of the Mun (Minmus, which is annoying, nor any actual moon, although honestly I could care more).

Is there any way to find out the exact intial position of the Mun and Minmus at the start of the game ?

I guess I could start a new game and try to find out with a screenshot, but that would be slightly unscientific.

Thanks to everyone !

[Kasuha]

Trajectory optimization calculators such as Alexmoon's calculator definitely know these positions so you might try to check its source code.

Or you may start using the calculator instead if it was for the same purpose.

Edit: found them for you.

[Sovnheim]

Aaaaah I definitely didn't think of it thanks !

Now i'm curious to understand how game makers defined their longitude 0°.

I assumed that Kerbal Spaceport would be the reference point but it seems that it is not.

Thank you for the help !

[Mr Shifty]

There's also this spreadsheet, which lists all the parameters for all of the bodies:

https://docs.google.com/spreadsheet/ccc?key=0AnK-FEkHU7FOdEZyQVA3NXRiT2l5WGY1dDVla1VRaXc&usp=sharing

To get the Mun's and Minmus's initial phase angles, I believe you're going to want to look at its Mean Anomaly at Epoch, which is 0.9. Since they both have circular orbits, the mean anomaly is the same as the phase angle (in radians.)

Mun: 0.9

Minmus: 1.7

They can't use Kerbal Space Port as a reference for this angle because Kerbin rotates. The angles are measured relative to a fixed orientation in space, which I assume is related to the coordinate system the planetary system is laid out on in code. In other words, I believe there's some arbitrary line drawn from the Sun, down the plane of the ecliptic, which marks angle zero. For each planet, their reference line is parallel to that line (but inclined if their orbit is inclined.) If all of the bodies had a zero MAaE, they would start out all in a straight line (looking from above) leading from the Sun outward.

[Kryxal]

I think the surprise is that KSC isn't also aligned to that same orientation to start...

[cantab]

Is Kerbin's prime meridian aligned to said orientation at the start? That would make sense, and then KSC isn't at the prime meridian because the developers got the map first, with its meridian already defined, then decided where to put the space centre.