The colour of the sky

  • #1
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
 

Answers and Replies

  • #2
berkeman
Mentor
59,059
9,157
Thread closed for Moderation...
 
  • #4
berkeman
Mentor
59,059
9,157
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?
 
  • #5
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.
 
Last edited:
  • #6
1,621
230
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.
 
Last edited:
  • #7
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?
 
Last edited:
  • #8
1,621
230
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.
 
  • Like
Likes Chinspinner

Related Threads on The colour of the sky

  • Last Post
Replies
11
Views
720
  • Last Post
2
Replies
43
Views
10K
  • Last Post
Replies
7
Views
12K
  • Last Post
Replies
3
Views
2K
Replies
3
Views
3K
Replies
6
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
2
Views
2K
Replies
9
Views
1K
Top