Orbital Element Confusion: MeanLong, EqAscNode, RotOffset

[Darkstone]

To Whom It May Concern:

I would appreciate some assistance in deciphering some of the planetary orbital data in Celestia's solarsys.ssc file. Apparently, the program uses a slightly different set of orbital elements and conventions from those I am familiar with. Though I've consulted the introduction and found it useful to a degree, a few questions linger in my thoughts.

I noticed, first of all, that Venus' rotation wasn't specified as retrograde; however, a quick glance at its near-180-degree obliquity led me to assume that "flipping the planet over" is Celestia's convention for specifying retrograde rotation. But then why is Earth's obliquity (though by all means correct) a negative number?

Secondly, through the recognition of some of the "Radius" data, I was able to hypothesize the "Atmosphere" and "CloudHeights" were measured in kilometers as well. But can someone confirm the unit of measurement for "CloudSpeed?" Kilometers per hour perhaps?

Unfortunately, there are three orbital elements that I could make no sense of whatsoever: "MeanLongitude," "EquatorAscendingNode," and "RotationOffset." Can someone define these terms for me? How do they relate to the more commonly used elements of mean anomaly, meridian position, and sidereal rotation rate? Would it be too much to ask for a diagram and/or a textual reference? I am avidly interested in this subject, and if there exists a book or website from which I could glean the relevant information, I would LOVE to read it.

Thanks kindly.

Darkstone

[selden]

I noticed, first of all, that Venus' rotation wasn't specified as retrograde; however, a quick glance at its near-180-degree obliquity led me to assume that "flipping the planet over" is Celestia's convention for specifying retrograde rotation. But then why is Earth's obliquity (though by all means correct) a negative number?

A partial answer is in the "Preliminary User's FAQ", Q/A#25. It's a "sticky" near the top of the Celestia User's Forum.

Secondly, through the recognition of some of the "Radius" data, I was able to hypothesize the "Atmosphere" and "CloudHeights" were measured in kilometers as well. But can someone confirm the unit of measurement for "CloudSpeed?" Kilometers per hour perhaps?

"Data file guides" (including for SSC files) are available on the Celestia Motherlode, on the documentation page at http://www.celestiamotherlode.net/catalog/documentation.html