Tidally-Locked Planets

[Diamond]

Hey Guildies, I'm starting work on a map of a tidally-locked Earth-like planet. It orbits a binary star and is a little further away from them than Earth is from the Sun.

My question is this: assuming the overall output of light and heat of the binary stars feels about the same to people on that planet as they'd experience when standing on our Earth, what would you say would be the diameter of the area exposed to the sun? How many miles from one side to the other? Like, if you started out at one edge where the sun was barely visible as a fingernail on the horizon, how many miles would you walk in a straight line until you got the same view from the other direction?

Also, how broad would you say the 'shadow zone' between actual 'day' and full 'night' would be?

Math is not my strong suit.

Visual aid attached:

[Mouse]

Wouldn't that depend largely on how big/small wide/narrow you want it to be?

Or are you absolutely intent on scientific accuracy?

[Diamond]

I'm not intent on scientific accuracy to the detriment of everything else, but I would like it to make sense. How did you figure out the scale, etc on your tide-locked planet?

[Mouse]

Ok then, if you're feeling nice and wide awake, you could start here with this discussion on exactly the same topic and work up to examine the scientific papers linked in the second answer?

(It made my brain all weird and I had to give up!)

[Diamond]

Ohhhhh... that will be MOST helpful. Thank you, Mousie!

[Mouse]

You're welcome

[johnvanvliet]

planets around binary or trinary star systems have rather chaotic orbits that ARE NOT stable over time

then there is the issue of what star the locked one orbits

for a planet to be about earth mass of 1 and in the liquid water zone and LOCKED that star needs to be a VERY small and dim star
as in a red dwarf ( not the ship )

that means that this star then will orbit the Primary star -- likely giant heavy mass star ( think about 50 to 100+ solar masses )

but for that locked planet to be even fairly stable the small star will need to be in a LONG circular orbit

even then the orbits of the system will be rather randomish

i would not expect anything more complex that "blue algae " ( pond scum ) to have evolved in a system like that

[Mouse]

Oh D!

Gloopy green bug eyed.... er... green things

[Azélor]

John is right, it's impossible to have such system.
In order to be stable the binary couple needs to be close to each other and the planet as far away as possible. Too far to be tide locked.
This minimize the gravitational pull when one star become close to the planet. It would act like a magnet and could draw the planet ever closer until it's disintegrated.
Or the planet could get ejected from orbit and freeze.

But assuming your planet orbit around a star that also orbit around a bigger star, then yes it's possible.
Pluto Charon is a stable system and Charon is 12% the mass of Pluto.
Now if your little star is a red dwarf with a mass around 0,12 solar masses
and the other star is similar to the Sun or a little bigger, you end up with a similar mass ratio between the 2 partners.

That can be stable as well. Just like the Moon orbits around the Earth, orbiting around the Sun. As long as your planet is not too far away from the red dwarf, otherwise it will escape it's gravitational pull.
The only problem I can't figure out without a software is the distance between all these objects to allow life on the planet, or if it's even possible at all.
My software Universe Sandbox should be able to give me an answer.

[Azélor]

Another test. The planet orbits at 7m km from the red dwarf and it takes about 11 days to make a full revolution. Could round it down to 12, 4 days for each season
The star is based on Wolf 359, a somewhat small red dwarf, but nothing wrong with it.
The problem is the tendency to have flares which emits nasty stuff like gamma ray.
Wikipedia tells me that it mostly happens right after the star birth. So it only last about 1 billion years. Barely a heartbeat for a red dwarf.

And in case you wonder, the planet can't have a moon.