Night and day on Regina

[Otronatis]

I've just finished reading the section on Regina in Behind The Claw, and I'm wondering what the "cycle" of day and night looks like on the planet (or it should be called a moon, I guess).

So Regina is orbiting a gas giant, which is itself orbiting binary stars. For that alone, I imagine it must mean that on top of the night/day cycle coming from the spin of Regina (assuming it's not tidally locked, but I've seen no mention of that), it must have a long night for the whole time the gas giant is between it and those stars. How long that long night goes depends on the time it takes for Regina to make one revolution around the gas giant, but I'd assume it must be at least a few months? So in that configuration, you have a few months of pitch black, then some shorter time with night and day but with the days having at first very little light, coming a bit stronger every day, then a regular cycle of night and day when the gas giant is not interfering anymore, then days start to dim again until the next long night start.

But then, there is Darida, the third star orbiting around the whole system! This can't be fast, I'd expect it to take decades to perform one revolution around the binary stars, maybe? So that would mean that there are long period of months or maybe years during which Regina is almost always in daylight, and similarly long period during which the behavior described in my previous paragraph is observed? Do I read that correctly?

 

[Vormaerin]

IIRC, the companion star for Regina's primary is a brown dwarf? Aptly named Speck. Darida is 5000 AU away and a red dwarf. It's a bright star, not a sun, as far as Regina goes.

So the real question is mainly how often Assiniboia blocks the primary.

 

[CordwainerFish]

IIRC, the companion star for Regina's primary is a brown dwarf? Aptly named Speck. Darida is 5000 AU away and a red dwarf. It's a bright star, not a sun, as far as Regina goes.

Unless I dropped a decimal, it'll be brighter than Venus but not as bright as the Moon (in most phases).

So the real question is mainly how often Assiniboia blocks the primary.

Depends on the inclination of Regina's orbit, either once per local day [1] or for two seasons per local year. More to the point, the eclipses will be brief - the eclipses of Jupiter's Galilean satellites last 2-5 hours. (You can observe them yourself with a good pair of binoculars. I would recommend a tripod.)

[1] Assuming Regina is tide locked, which feels like a safe assumption.

 

[Otronatis]

IIRC, the companion star for Regina's primary is a brown dwarf?

In my book (MgT2 Behind the Claw), it only says "a dwarf companion", without specifying color.

Darida is 5000 AU away and a red dwarf

Oh, ok! There too, it's not very clear in this book, it just says it's "in a very distant orbit", and the picture (cf attachment) made me think it would have some serious impact, but I guess distances are not to be considered to the proper scale.

More to the point, the eclipses will be brief - the eclipses of Jupiter's Galilean satellites last 2-5 hours

I don't understand this. Does it mean that Regina would go around around the gas giant in just a few hours? Or is it because the stars are so massively bigger than the gas giant that you need a perfect alignment to have obscurity?

 

[Vormaerin]

Even a red dwarf that close to a type F star wouldn't change night and day, just add a tiny amount of light to the already bright primary. The Traveller wiki says Speck is a brown dwarf, but I am not sure it's sourcing on that. There's been so many versions of Spinward Marches books over the decades...

For companion stars "close" usually means "holding hands with the other star", "far" usually means outer system, and "distant" usually means "way off somewhere else in the same hex".

 

[CordwainerFish]

I don't understand this.

You can look up the times of Jupiter's moons going into and out of eclipse.

 

[Geir]

So I don't know if this counts as canon (but it was published by FFE, so it ought to be)
From Imperiallines No. 6 (p.10) Regina's description includes:

The planet has a 26.4 hour day and is 2.2 AU from its central​

star. The local year is about 1,066 standard days. Being a​

satellite of a gas giant, it has no appreciable eccentricity. Its​

axial tilt is 22 degrees.​

Not sure I agree with the eccentricity logic, but there you have it.

Also, from MegaTraveller Referee's Manual, page 21, the Regina system is laid out. Regina is in Orbit 55 of the large Gas Giant Assiniboia, which occupies Orbit 4 of the Lusor/Speck Primary and Companion stars (which would make it 1.6 AU from the stars in MegaTraveller terms, not 2.2 AU, but what do you want? Consistency?).

Just to make it more difficult, on page 29, same book, an Orbit around a planet is defined as a multiple of the radius, not the diameter of the parent world, which strikes me as inconsistent and annoying. It may have been corrected in later errata. But nowhere does the diameter (or radius) of a gas giant get defined. In fact, explicitly on page 28:

... roll ID On a result
of 1, 2, or 3, the planet is a​

Small Gas Giant, on a result of​

4, 5, or 6, the planet is a Large​

Gas Giant No other attributes​

are generated for gas giants​

​

<This posting is sponsored by the December friendly plug for the new World Builder's Handbook, available from Mongoose, where, among other things, attributes of gas giants are further defined>

 

[Anstett]

and

 

[Otronatis]

So I don't know if this counts as canon (but it was published by FFE, so it ought to be)
From Imperiallines No. 6 (p.10) Regina's description includes:

Awesome, thanks for the reference!

The planet has a 26.4 hour day

So that would mean it has a simple and regular cycles of day and night similar to Earth, right? That sounds counter-intuitive, given the configuration of the system. Then again, science and intuition are often enemies. Is any of you an astronomer, for whom the subject is obvious, by any chance?

<This posting is sponsored by the December friendly plug for the new World Builder's Handbook, available from Mongoose, where, among other things, attributes of gas giants are further defined>

Thanks. I'm waiting for it to be available on paper. Delivery fees to here are a bit too expansive to order books one by one, and you can't mix preorders and regular orders.