Kepler 1st law vs Dune's orbit

[adammada]

http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion

The orbit of every planet is an ellipse with the Sun at one of the two foci.

Fact A: shape of Dune orbit is circle (i measured it, you can draw SQUARE around it)

Fact B: Circle is special form of ellipse, where both foci are in one place (center).

Fact C: Kerbol is not in center of that circle.

Conclusion: Dune orbit (and maybe other planets, cause only Moho's orbit is visible ellipse) violates Kepler 1st law.

Edited September 23, 2012 by adammada
i meant square, not rectangle.

[Melfice]

Have a look at Duna's peri- and apoapsis. (or easier yet, look at it's orbital speed: it changes! You may need to go into high warp)

You'll find the planet's orbit is, in fact, an ellipse.

Funny you should choose Duna, however.

Kerbin's orbit is actually a perfect circle.

[Bluejayek]

Melfice, adam is trying to say that Dune's orbit is a circle with the center not at kerbol.

However adam, Fact B: a rectangle can be drawn around any ellipse; you can draw a SQUARE around a circle.

[UmbralRaptor]

Going by the info pulled out of the game, Duna's eccentricity is only ~0.05. That's not easily visible.

[maltesh]

Duna's orbit is elliptical, with an eccentricity of 0.051. Its distance from the center of the sun ranges from 19.4 million kilometers at periapsis to 21.4 million kilometers at apoapsis.Blast, beaten. At any rate, of all the planets, only Kerbin is in a truly circular orbit. Kerbin's moons and the three innermost moons of Jool are also in circular orbits.

The black figure is a circle with radius 1 and center (0,0). The red figure is an ellipse with semimajor axis 1 and eccentricity 0.051. Its foci are (0,0) and (0, 0.102).

Edited September 23, 2012 by maltesh

[phoenix_ca]

The other problem is perspective. Viewed from the right perspective, any ellipse can look like a circle, if the viewer is deprived of depth-perception (which we are; our screens are flat...and KSP doesn't output stereo images). That, combined with the small eccentricity, makes it quite easy to see how one might mistake it's orbit as circular. The distortion caused by the field-of-view of the game's camera probably doesn't help either.

[AncientAstronaut]

This thread is such a fail. Duna's orbit is not a circle with the sun off center. It's slightly eccentric.