Question about tidal locking

hems303

hems303
Hi CMDR's

Yesterday I landed on Kuk B 3 (Selene Jean's hangout) with the planet bathed in bright starlight, logged off overnight and returned today and the planet (side) is now in complete darkness.
I assumed that a tidally locked planet would NOT have a day/night cycle.
Now I know the Kuk system is a binary star system.......
Q: Would I be actually correct in thinking the day/night cycle on planet Kuk B 3 is coming from the main star and not the secondary star around which the planet is tidally locked? Have FDev really been this clever with the lighting code in ED?

Any answers/insight very welcome. o7
139675
 
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HAMM3R

HAMM3R
[swedish hat on]"Kuk" 🤭 [/swedish hat off]

But yeah, I'd say it was the B2 blocking the light. Those binaries are actually quite nice when you catch the eclipse from the surface.
 

Ashnak

Ashnak
SInce the other orbital parameters (major axis and rotational period) most certainly refer to the binary pair, that tidal lock will also refer to the binary pair.
 

Rampant

Rampant
The tidal locking of B3 is with B2. All this means is that B3 is locked in such a way that the same side of the planet always faces B2.

This doesn't stop the B2/B3 pair from rotating around one another as they orbit the star. This gives a day/night diurnal cycle to B3 - where it's total day duration is roughly the same duration as its orbit around B2.
(roughly the same = because B2 also moves around the star - so there is a "sidereal" element that compliments the rotation of the planet due to it's shift around the main star)
 

Webgear

Webgear
A planet tidally locked to a star would need to be fairly close to the primary, like the orbit of Mercury around Sol. Being tidally locked to another non-star body like Earth-Moon system or Pluto-Charon is probably way more common in the universe.
 

Random Providence

R
Yep, from the semimajor axis being so small (0.00 AU) you can be sure the details are relative to the sister planet not the parent star. The details for the pair’s stellar orbit aren’t shown at all.

And to make things more interesting, B2 and B3 have significant eccentricities in their orbits around each other, so while they’re tidally locked to each other the locks are not 1:1 like Luna is to Earth. Instead B2 is 3:2 (same as Mercury) and B3 is 9:7.
 

Stealthie

Stealthie
hems303 said:
Q: Would I be actually correct in thinking the day/night cycle on planet Kuk B 3 is coming from the main star and not the secondary star around which the planet is tidally locked? Have FDev really been this clever with the lighting code in ED?
Click to expand...

Just to address this specific thing...

I know ED has had lighting in it that worked like this but I'm not sure if it still does, or whether I'd say it worked well.

I'm a frequent visitor to Marco Qwent.
I'll often arrive when it's "night" at Qwent's base - the far side of Lucifer is facing Sirius B.
From orbit, there's a proper day/night divider on Lucifer, with Qwent's base right in the middle of the night-side.
When I land, however, it suddenly becomes "daylight" on the surface, presumably as a result of the surface being lit by Sirius A.
A look at the Orrery (or just, y'know, up into the sky) confirms that Sirius A is visible from Qwent's base but it barely looks any brighter than more distant stars so I'm not sure the amount of light it's providing is appropriate.

Also, it's been a few months since I've visited Qwent's base (or anywhere else in the ED galaxy) so this might have changed now but it was this way immediately after the new lighting changes at the end of last year.
 

Rampant

Rampant
Rampant said:
The tidal locking of B3 is with B2. All this means is that B3 is locked in such a way that the same side of the planet always faces B2.

This doesn't stop the B2/B3 pair from rotating around one another as they orbit the star. This gives a day/night diurnal cycle to B3 - where it's total day duration is roughly the same duration as its orbit around B2.
(roughly the same = because B2 also moves around the star - so there is a "sidereal" element that compliments the rotation of the planet due to it's shift around the main star)
Click to expand...

BTW...

I just illustrated that to myself, from first principles using 2 apples for B2 and B3 - by rotating them around on my desk- and imagining my monitor was the star.
Made it a bit easier to type the description of the sidereal element, straight after visualising with props on my desk. (From memory, I think "sidereal" is the correct term - someone correct me if that's the wrong word, please.)

I will now proceed to eat apple.
 

Sapyx

Sapyx
hems303 said:
Q: Would I be actually correct in thinking the day/night cycle on planet Kuk B 3 is coming from the main star and not the secondary star around which the planet is tidally locked? Have FDev really been this clever with the lighting code in ED?
Click to expand...

ED does not model multiple-source lighting from multiple stars in a system. But there is some kind of luminosity algorithm the game uses to determine "which is the brightest star" at any given point in a star system, and it would then use that star as the lightsource. It usually means "whichever star is closest", but there are some obvious exceptions. Giant stars are one such exception; the giant star is almost always the light-source for a star system, even if there are closer stars.

In the case of Kuk, I'm pretty sure that the secondary star Kuk B is going to be the lightsource for Kuk B2/B3. It's only slightly dimmer than Kuk A, but much closer.
 

Sapyx

Sapyx
And one final point about "tidal locking". What we normally think of when we think of "tidal locking" is a 1:1 orbital resonance: the world rotates once for every orbit around the thing it orbits around. But it is possible to be "tidally locked" into some other resonance

Mercury, for example, is tidally locked into a 3:2 resonance (two rotations for every three orbits), primarily because a 1:1 orbital resonance is not stable for a planet with an orbital eccentricity as high as Mercury has. This isn't reflected by a "tidal locking" tag for Mercury in-game, but it is nevertheless fairly common to find planets that are "tidally locked" to their star, for which the day length and year length are significantly different.
 

hems303

hems303
WOAH! Thanks guy's your explanations have really opened my eyes (and intellect) on the astronomical ''dance'' by the represented bodies. For all our moans the system FDev have implemented really is cool (IMHO). The fact that B 2 and B 3 are the tidally locked ''partners'' hadn't occurred to me... but I now fully understand the diagrammatic displayed by the System Map... hadn't really cottoned on fully. Cheers again o7 o7 o7
 

hems303

hems303
Northpin said:
Moon is tidal locked to Earth.
Still Moon has Day/Night with a 14 days period.
Click to expand...
Lets see if my master class kindly supplied by all above has paid off......You say; ''Still Moon has Day/Night with a 14 days period.''.......I guess; because the Earth (round which the moon travels) is not tidally locked to the sun... ..... the dark side of the moon is only dark from our perspective...not the moon's.....eh? (Pink Floyd's album will never be the same again...lol)

EDIT: See CMDR Northpin's reply to this, below; I was trying to say pretty much the same, he just put it very much better. 👍

''Not really. It's because Moon orbits the Earth in 28 days and it is tidal locked to the Earth, but not to the Sun. So while the Moon is orbiting the Earth, the "dark" side is in broad daylight when Moon is between Sun and Earth and it is in broad darkness when the Moon goes half orbit and Earth is between Moon and Sun.''


(I must admit the answers to my thread have really opened my eyes to the complexities of celestial ''dynamics'' inside ED and in RL, especially regarding orbital resonance which I had assumed was inevitably 1:1 resonance.... why would it be!)

o7
 
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Stealthie

Stealthie
metatheurgist said:
Funny thing about Kuk 2/3. Passing through the shadow of one of those bodies will turn off the lighting for the other. Magic! 😂
Click to expand...

I've noticed that in various other places too.

A moon in the shadow of a planet and when you move out of the shadow of the planet, suddenly the moon gets lit up too. :unsure:
 

Rampant

Rampant
hems303 said:
Lets see if my master class kindly supplied by all above has paid off......You say; ''Still Moon has Day/Night with a 14 days period.''.......I guess; because the Earth (round which the moon travels) is not tidally locked to the sun... ..... the dark side of the moon is only dark from our perspective...not the moon's.....eh? (Pink Floyd's album will never be the same again...lol)

o7
Click to expand...

"Dark" side of the moon is a bit of a misnomer.

The dark part is not fixed in any way, and that's why we have new, crescent, half, gibbous and full moons when viewed from Earth.

The half of the moon that faces Earth is fixed, so we always see the same hemisphere. The bit we don't see is more properly called the "Far" side of the moon. The far side also has day and night...
 

GeneralIdea1964

G
hems303 said:
Hi CMDR's

Yesterday I landed on Kuk B 3 (Selene Jean's hangout) with the planet bathed in bright starlight, logged off overnight and returned today and the planet (side) is now in complete darkness.
I assumed that a tidally locked planet would NOT have a day/night cycle.
Now I know the Kuk system is a binary star system.......
Q: Would I be actually correct in thinking the day/night cycle on planet Kuk B 3 is coming from the main star and not the secondary star around which the planet is tidally locked? Have FDev really been this clever with the lighting code in ED?

Any answers/insight very welcome. o7
View attachment 139675
Click to expand...
Yes FD have been that clever.
I remember a post on one release saying they had to calculate view with many light sources. I seem to remember it was a very high number and included multiple stars and light reflected off nearby planets and moons, light from space stations and even yours and other ship lights
Pretty impressive really.
 

Northpin

Northpin
hems303 said:
.I guess; because the Earth (round which the moon travels) is not tidally locked to the sun
Click to expand...

Not really.
It's because Moon orbits the Earth in 28 days and it is tidal locked to the Earth, but not to the Sun.
So while the Moon is orbiting the Earth, the "dark" side is in broad daylight when Moon is between Sun and Earth and it is in broad darkness when the Moon goes half orbit and Earth is between Moon and Sun
 
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