[Dragaera] Dragaera and Moons **Minor Vallista Spoiler, nothing plot related**

[Jon Lincicum]

----- Original Message -----

From: "dusty--- via Dragaera" <dragaera at lists.dragaera.info> 
To: "Jerry Friedman" <jerry_friedman at yahoo.com> 
Cc: dragaera at lists.dragaera.info 
Sent: Monday, November 6, 2017 3:35:16 PM 
Subject: Re: [Dragaera] Dragaera and Moons **Minor Vallista Spoiler, nothing plot related** 

> 
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> From: Scott Schultz via Dragaera <dragaera at lists.dragaera.info> 
> 
>> -----Original Message----- 
>> From: Dragaera [mailto:dragaera-bounces at lists.dragaera.info] On Behalf 
>> Of 
>> Jerry Friedman via Dragaera 
>> Sent: Saturday, November 04, 2017 1:47 PM 
>> To: dragaera at lists.dragaera.info 
>> Subject: Re: [Dragaera] Dragaera and Moons **Minor Vallista Spoiler, 
>> nothing plot related** 
>> Sent from my iPhone please excuse typos 
>> > ----- Original Message ----- 
>> > 
>> > From: "Konrad Gaertner via Dragaera" <dragaera at lists.dragaera.info> 
>> > To: dragaera at lists. To.info 
>> > Sent: Friday, November 3, 2017 5:04:29 AM 
>> > Subject: Re: [Dragaera] Dragaera and Moons **Minor Vallista Spoiler, 
>> > nothing plot related** 
>> > 
>> >> On 11/2/2017 10:19 PM, Jon via Dragaera wrote: 
>> >> Spoiler Space 
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>> > [snip] 
>> > 
>> >>> to the rotational period of the planet itself. Effectively, it means 
>> >>> this moon must orbit at a point close to (but not exactly at) the 
>> >>> natural altitude for a fully geosynchronous orbit. It cannot diverge 
>> >>> from this orbital period by more than about 2 hours per day (given 
>> >>> Dragaera's 30-hour day), however, or else it would always take fewer 
>> >>> than nine days to appear again in the sky at any particular point on 
>> >>> the 
>> >>> surface of the planet. 

<snip> 

> Whatever the reason for 
> its orbit, it's entirely artificial. It could be some geosynchronous orbit 
> that makes sense when you're directly underneath it, but that Dolivar and 
> the nascent Empire only see every so often when the planet's natural 
> wobble brings it into visible range. It could be some highly elliptical 
> orbit, like a comet. Note that the wording is that it will rise in 
> "another nine days", not that it rises EVERY nine days. We don't really 
> know the period of Littlemoon (even if Dolivar does know it). 

Allow me to clarify. The nearly-geosynchronous orbit theory does not in any way involve "wobble" (also called precession). 

A fully geo-stationary orbit consists of a body that orbits another larger body at exactly the right distance and orientation for the satellite to maintain a constant position overhead of a fixed point on the larger body's surface. (A truly geostationary orbit is also only possible on a line with the planet's equator, whereas geosynchronous orbits can be anywhere, as long as they're moving in the same direction as the rotation of the planet.) 

The orbit of a satellite that is at a lower altitude will move faster, and to an observer on the ground, will appear to move westward across the sky. A satellite in a higher orbit will move more slowly, and appear to move eastward, instead. This is because the moon is falling out of synch (either by going a little too fast, or a little too slow) from this perfect balance. An altitude difference of only a few feet away from optimal will cause this effect to become visible over time. 

The closer the moon is to the "magic" altitude for a fully geo-synchronous orbit, the more slowly it will appear to move across the sky from the perspective of a ground observer. This means it could take weeks, months, years, or even cycles for the difference in the revolutionary period of the satellite from the rotational period of the planet to result in the return of the satellite to its "starting point". Note also, the moon itself does not need to be rotating at all in this scenario. 

And no, we do not know the maximum amount of time that Littlemoon stays out of view when it sets. But we do know that it has to stay down for at LEAST nine days, which means the orbital altitude must be within several hundred feet of the geosynchronous point at most. 

> 
<snip> 

> I'm having trouble imagining a planet wobbling enough to bring a 
> geosynchronous satellite into and out of view on a scale of days. 
> A constellation wouldn't just appear in the morning. The time of day it 
> appeared would depend on the time of year. 

Precession is a phenomenon that is caused by instability in the rotational axis of a spinning body that causes the orientation of its axis to draw out a circle or figure-eight pattern. (This is the reason why Polaris will no longer be the "North Star" 7,000 years from now, and also why we can at times see different parts of the face of the moon, even though it is constantly rotating in tidal lock with Earth. The "wobble" causes us to see somewhat over 58% of the moon's surface at various times. ) 

This couldn't ever by itself cause a moon to appear to rise or set, unless one was standing at or near a pole of the planet the moon was orbiting, and the precession were happening abnormally quickly. 

Also, I'd like to stress that just because an object is orbiting very close to a natural geosynchronous point, that is far from sufficient to prove that it is artificial in origin. Geosynchronous orbits are generally very stable, and easy for objects to fall into quite naturally. 

Majikjon