The colour of the sky

[Chinspinner]

Hi,

If you were to half Earth's orbit around a K4.5V main sequence star (assuming the same composition and density of atmosphere), what colour would the sky be?

Thanks in advance.

Chinspinner

 

[berkeman]

Thread closed for Moderation...

 

[jedishrfu]

Reopened not homework related.

 

[berkeman]

Hi,

If you were to half Earth's orbit around a K4.5V main sequence star (assuming the same composition and density of atmosphere), what colour would the sky be?

Thanks in advance.

Chinspinner

What are your thoughts?

 

[Chinspinner]

What are your thoughts?

I forgot to mention that the star has a luminosity of about 0.25, hence the earth-like planet being in closer orbit.

Part of me is thinking that light will scatter in the same way as on Earth towards the blue wavelength. However, the light the star is emitting will be more towards the red wavelength, and I am not sure if the relative proximity of the planet will make a significant difference (towards violet).

I am imagining a more diffused light and perhaps a more yellow sky, but this is what I need help with.

 

[snorkack]

I forgot to mention that the star has a luminosity of about 0.25, hence the earth-like planet being in closer orbit.

With K5, it is roughly the description of epsilon Indi. Whose colour index is 1,06.

Part of me is thinking that light will scatter in the same way as on Earth towards the blue wavelength. However, the light the star is emitting will be more towards the red wavelength, and I am not sure if the relative proximity of the planet will make a significant difference (towards violet).

No. There is nearly no extinction or reddening in the nearly empty space inside Earth orbit.

I am imagining a more diffused light and perhaps a more yellow sky, but this is what I need help with.

Less blue, yes, but I´m imagining less diffused light. Because there is less blue light to be diffused.

 

[Chinspinner]

With K5, it is roughly the description of epsilon Indi. Whose colour index is 1,06.

No. There is nearly no extinction or reddening in the nearly empty space inside Earth orbit.

Less blue, yes, but I´m imagining less diffused light. Because there is less blue light to be diffused.

Thanks. It is Epsilon Indi, so I would also have more distant brown dwarves to add into the mix. So we are effectively looking at an earth-like sky but perhaps a lighter shade of pale and a reddish sun?

 

[snorkack]

Thanks. It is Epsilon Indi, so I would also have more distant brown dwarves to add into the mix. So we are effectively looking at an earth-like sky but perhaps a lighter shade of pale and a reddish sun?

Yes.
Note that ALL these effects happen on Earth as the altitude of Sun decreases. Sun gets both dimmer and redder as it approaches horizon in the evening, the sky also gets less bright as well as a paler shade of blue.

But these happen at slightly different rates. Notably, as Sun sinks, the brightness of Sun decreases relative to the decreasing brightness of sky above. Whereas Epsilon Indi high in sky may look like Sun low in the sky in its brightness and colour, but the brightness and colour of the sky may look like Earth sky with Sun even lower. So the shadows cast by Epsilon Indi should look slightly more contrasting than shadows cast by Sun.