Question regarding red giants

[Regiomontanud]

In order to illustrate the size of a red giant star like Antares or Arcturus compared to our sun it is sometimes stated that if said red giant was in the center of our solar system, it’s surface would extend to the orbit of earth, mars etc. 

Once our sun will have reached the state of a red giant it might or might not „swallow“ earth. 
But - just hypothetically - would you even notice you were „inside the sun“?

I imagine that with sun‘s mass distributed across such a huge volume the density of its plasma, atmosphere, outer shell or whatever call it then ought to be quite low. 
 

So I wonder if you still could see some kind of sky through the presumably thin outer layers of sun‘s atmosphere - that is if your position on earth is facing away from the sun?

Thanks for your thoughts and greetings

Ralph

[andrew s]

While the density and pressure is low in the outer atmosphere it is at about 3000 to 5000k

I think we would notice that.

Regards Andrew 

Edited October 20, 2020 by andrew s

[billyharris72]

We would definitely notice, but the point is a fair one in the abstract. Gasses in space at very low pressures can be at over a million Kelvin, yet the space itself could be (hypothetically) interpreted by us as "cold" if there isn't enough of that gas. 

The Sun's Corona is an example of this. At about 1 million K it poses comparatively little threat to the Parker Solar probe, which will be travelling through it. What that is "worried" about is the 5800K photosphere - less hot but an awful lot more of it.

But for us - I have not actually thought it through in any detail, but I'd imagine the radiation and solar winds from a red giant would strip the atmosphere and turn every living thing on Earth to a crisp quite some time before any of this became a worry.

Billy.

[Waddensky]

Great question, great answers. As said: the density is not the problem, but the temperature is. In any case, long before the Sun swells to the size of the orbit of the Earth our atmosphere and oceans are evaporated. I can imagine that the Earth even deorbits due to the drag caused by the collision with solar gas particles.

Edited October 21, 2020 by Waddensky

[andrew s]

The sun will become so hot as it enters helium burning that it will boil off the oceans long before we are engulfed by it.  Regards Andrew 

Edited October 21, 2020 by andrew s

[markse68]

Strange question given you’d not survive for long in the temperatures but wasn’t the question if you’d be able to see out through the engulfing star? I imagine you probably would be able to but as the hot plasma itself would be glowing, the light pollution would be on another level! You’d likely need to extend the bortle scale

Edited October 21, 2020 by markse68

[andrew s]

Have a look at this https://www.google.com/url?sa=t&source=web&rct=j&url=https://phys.org/news/2016-05-earth-survive-sun-red-giant.html&ved=2ahUKEwi1xvLHvcXsAhXIMMAKHWcmBy4QFjAAegQIHRAB&usg=AOvVaw1UUmQyy_6K-mGipibVr4Lq

Regards Andrew 

[Gfamily]

A factor to be taken into consideration is the 'optical depth' of the stellar atmosphere, which depends on the amount of ionisation that determines how far light can travel before being absorbed and re-radiated. So; it's the free electrons that will prevent light from the exterior having a free path to your eyes. 

As recall, the 'surface' of a star is the depth at which a photon has a 70% chance of directly making it out of the star. 

Below that, even without the local radiation, you wouldn't be able to see the 'outside' universe (similar to the way that even thin cloud blocks our view of the night sky).

Edited October 21, 2020 by Gfamily