<p>How rare is it to have 2 stars or 2 celestial bodies at least as big as our moon and sun in the sky of a habitable planet? What are the chances of both?</p>

CC BY-SA 4.0
2024-02-02T14:39:32.967Z
Isn't every star a sun? Do moons of other planets count as moon in our sky?
planetmaker
CC BY-SA 4.0
2024-02-02T14:52:16.127Z
planetmaker: OP probably wants to know about binary star systems, and number of moons around a habitual planet itself. Otherwise the number 2 would be ridiculously low.
DarkDust
CC BY-SA 4.0
2024-02-02T16:04:13.920Z
@DarkDust is it obviously low? Of the 4 terrestrials planets in our solar system, one of them has two moons, and one has one moon, two have no moons. That’s the entirety of our sample size, we can’t really make a big judgement based on that.
Topcode
CC BY-SA 4.0
2024-02-02T16:06:53.110Z
Who says that there can't be life on a moon around a planet like Jupiter or Saturn? So there would be a (or the) stars in the sky, the planets, the "own" planet and its other moons
planetmaker
CC BY-SA 4.0
2024-02-02T18:14:30.010Z
Like, Mars's Deimos looks like a double-size Venus from the surface, not like a big full moon, and it's *booking* -- just under one orbit per day.  Meanwhile a distant binary could have an orbital distance between the stars that exceeds a lightyear, so you'd have one sun and one very bright star that is sometimes visible during the day, but you won't get a binary sunset out of it. Meanwhile a close binary makes the orbital physics a little hinky (technical term) and you may not be able to get a stable orbit within the habitable zone.
Darth Pseudonym
CC BY-SA 4.0
2024-02-03T00:12:47.197Z
To our current understanding, most stars are in a binary system. However, we cannot reliably estimate the rarity of twin moons, since we only have our Solar System to go off of. We can barley image exoplanets, let alone their satellites. Regardless, based on our current information, 1 out of 8 planets (Mars) have this trait, if you want to count dwarf moons. If you're talking about full-sized moons like our own, no planet in the solar system has exactly two, they either have more or fewer. According to National Geographic, 16 out of 1780 exoplanets are in a habitable zone. So pretty rare.
4NT4R3S
<natural-satellites><binary-star><habitable-zone>
Two Suns vs Two moons in the Sky
Justintimeforfun
# Two Suns vs Two moons in the Sky

(Asked by: username_0 on 2024-02-02)

How rare is it to have 2 stars or 2 celestial bodies at least as big as our moon and sun in the sky of a habitable planet? What are the chances of both?

**Tags:** natural-satellites, binary-star, habitable-zone
> **Comments:**
> **username_1**: Isn't every star a sun? Do moons of other planets count as moon in our sky?  
> **username_2**: planetmaker: OP probably wants to know about binary star systems, and number of moons around a habitual planet itself. Otherwise the number 2 would be ridiculously low.  
> **username_3**: @DarkDust is it obviously low? Of the 4 terrestrials planets in our solar system, one of them has two moons, and one has one moon, two have no moons. That’s the entirety of our sample size, we can’t really make a big judgement based on that.  
> **username_1**: Who says that there can't be life on a moon around a planet like Jupiter or Saturn? So there would be a (or the) stars in the sky, the planets, the "own" planet and its other moons  
> **username_4**: Like, Mars's Deimos looks like a double-size Venus from the surface, not like a big full moon, and it's *booking* -- just under one orbit per day.  Meanwhile a distant binary could have an orbital distance between the stars that exceeds a lightyear, so you'd have one sun and one very bright star that is sometimes visible during the day, but you won't get a binary sunset out of it. Meanwhile a close binary makes the orbital physics a little hinky (technical term) and you may not be able to get a stable orbit within the habitable zone.  
> **username_5**: To our current understanding, most stars are in a binary system. However, we cannot reliably estimate the rarity of twin moons, since we only have our Solar System to go off of. We can barley image exoplanets, let alone their satellites. Regardless, based on our current information, 1 out of 8 planets (Mars) have this trait, if you want to count dwarf moons. If you're talking about full-sized moons like our own, no planet in the solar system has exactly two, they either have more or fewer. According to National Geographic, 16 out of 1780 exoplanets are in a habitable zone. So pretty rare.  

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