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In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically, since there are maxima for the possible size of planets, for how close stable orbits can form, for how close you could orbit a given star, Roche Limit, etc...

--> Specifically, what is the maximum size in arc seconds at which a celestial body could appear in the sky for an observer on the surface? And what would that observed celestial body be? A very large moon? A twin-planet arrangement? Something else?

Assumptions:

• Let's assume that the observer stands on some celestial body (and they would like to survive).
• Body size/mass is such that it could be (made) habitable for humans.
• Proximity to the bodies star is such that the temperature can be manageable for humans given approx. current level of technology.
• The constellations of celestial bodies should be possible according to current science and stable at least in the short term.

E.g. standing on a sizeable moon looking up at the planet does count. Looking up at an incoming rogue planet 10 meters before impact obviously doesn't, since that arrangement is neither stable nor survivable.

Inspired by these questions...

• What could be the largest geosynchronous moon?
• Could We See a Lagrange Giant in the Sky?

In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically, since there are maxima for the possible size of planets, for how close stable orbits can form, for how close you could orbit a given star, Roche Limit, etc...

--> Specifically, what is the maximum size in degrees/arc seconds at which a celestial body could appear in the sky for an observer on the surface? And what would that observed celestial body be? A very large moon? A twin-planet arrangement? Something else?

Assumptions:

• Let's assume that the observer stands on some celestial body (and they would like to survive).
• Body size/mass is such that it could be (made) habitable for humans.
• Proximity to the bodies star is such that the temperature can be manageable for humans given approx. current level of technology.
• The constellations of celestial bodies should be possible according to current science and stable at least in the short term.

E.g. standing on a sizeable moon looking up at the planet does count. Looking up at an incoming rogue planet 10 meters before impact obviously doesn't, since that arrangement is neither stable nor survivable.

Inspired by these questions...

• What could be the largest geosynchronous moon?
• Could We See a Lagrange Giant in the Sky?

In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically, since there are maxima for the possible size of planets, for how close stable orbits can form, for how close you could orbit a given star, etc...

--> Specifically, what is the maximum size in arc seconds at which a celestial body could appear in the sky for an observer on the surface? And what would that observed celestial body be? A very large moon? A twin-planet arrangement? Something else?

Assumptions:

• Let's assume that the observer stands on some celestial body (and they would like to survive).
• Body size/mass is such that it could be (made) habitable for humans.
• Proximity to the bodies star is such that the temperature can be manageable for humans given approx. current level of technology.
• The constellations of celestial bodies should be possible according to current science and stable at least in the short term.

E.g. standing on a sizeable moon looking up at the planet does count. Looking up at an incoming rogue planet 10 meters before impact obviously doesn't, since that arrangement is neither stable nor survivable.

Inspired by these questions...

• What could be the largest geosynchronous moon?
• Could We See a Lagrange Giant in the Sky?

In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically, since there are maxima for the possible size of planets, for how close stable orbits can form, for how close you could orbit a given star, Roche Limit, etc...

--> Specifically, what is the maximum size in arc seconds at which a celestial body could appear in the sky for an observer on the surface? And what would that observed celestial body be? A very large moon? A twin-planet arrangement? Something else?

Assumptions:

• Let's assume that the observer stands on some celestial body (and they would like to survive).
• Body size/mass is such that it could be (made) habitable for humans.
• Proximity to the bodies star is such that the temperature can be manageable for humans given approx. current level of technology.
• The constellations of celestial bodies should be possible according to current science and stable at least in the short term.

E.g. standing on a sizeable moon looking up at the planet does count. Looking up at an incoming rogue planet 10 meters before impact obviously doesn't, since that arrangement is neither stable nor survivable.

Inspired by these questions...

• What could be the largest geosynchronous moon?
• Could We See a Lagrange Giant in the Sky?

In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically?

Assumptions:

• Let's assume that the observer stands on some celestial body (and they would like to survive).
• Body size/mass is such that it could be (made) habitable for humans.
• Proximity to the bodies star is such that the temperature can be manageable for humans given approx. current level of technology.
• The constellations of celestial bodies should be possible according to current science and stable at least in the short term¹.

--> Specifically, what is the maximum size in arc seconds at which a celestial body could appear in the sky for an observer on the surface?

What would that observed celestial body be? A very large moon? A twin-planet arrangement? Something else?

Inspired by these questions...

• What could be the largest geosynchronous moon?
• Could We See a Lagrange Giant in the Sky?

¹ I.e. No looking up at an incoming meteorite 5m before impact... ;)

In SciFi Art we often see planets/moons/stars fill enormous amounts of the visible sky. I'm wondering what the theoretical limit for this is realistically, since there are maxima for the possible size of planets, for how close stable orbits can form, for how close you could orbit a given star, etc...

--> Specifically, what is the maximum size in arc seconds at which a celestial body could appear in the sky for an observer on the surface? And what would that observed celestial body be? A very large moon? A twin-planet arrangement? Something else?

Assumptions:

• Let's assume that the observer stands on some celestial body (and they would like to survive).
• Body size/mass is such that it could be (made) habitable for humans.
• Proximity to the bodies star is such that the temperature can be manageable for humans given approx. current level of technology.
• The constellations of celestial bodies should be possible according to current science and stable at least in the short term.

E.g. standing on a sizeable moon looking up at the planet does count. Looking up at an incoming rogue planet 10 meters before impact obviously doesn't, since that arrangement is neither stable nor survivable.

Inspired by these questions...

• What could be the largest geosynchronous moon?
• Could We See a Lagrange Giant in the Sky?