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-   -   What colour the sky? (http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=39129)

Duke Craig June 6th, 2018 02:33 PM

What colour the sky?
 
Star Classes O B A F G K M,
Remember the Mnemonic: Oh Be A Fine Girl Kiss me.

However, what would be the colour of the sky under the various classes of stars?

(There are also several classes of star below M, including L, T and Y...)

Enjoy!

JimMarn June 6th, 2018 02:41 PM

Our G2-V star is yellow, but due to dust scatter in our upper atmosphere, the sky is a light blue.

I remember some 'true color' photos of Mars' atmosphere from one of the rovers.

You might find it on Astronomy Photo of the Day. I checked there and didn't find it. I used 'Mars' as the search word.

whulorigan June 6th, 2018 02:51 PM

Quote:

Originally Posted by Duke Craig (Post 587859)
Star Classes O B A F G K M,
Remember the Mnemonic: Oh Be A Fine Girl Kiss me.

However, what would be the colour of the sky under the various classes of stars?

(Yes I know there are several classes of star below M, including L, T and Y...)


Start by taking a look at these sites:


Basically, for an atmosphere of comparable composition and density to Earth, the sky will still be lighter to darker shades of blue, depending on stellar type. Increase in atmospheric density will tend to shift the wavelengths in a "redder" direction, and differing atmospheric composition will cause different wavelengths of light to be absorbed.

Duke Craig June 7th, 2018 01:01 AM

Quote:

Originally Posted by whulorigan (Post 587861)
Start by taking a look at these sites:


Basically, for an atmosphere of comparable composition and density to Earth, the sky will still be lighter to darker shades of blue, depending on stellar type. Increase in atmospheric density will tend to shift the wavelengths in a "redder" direction, and differing atmospheric composition will cause different wavelengths of light to be absorbed.

Thanks for the site links, very interesting. :oo:

aramis June 7th, 2018 05:31 PM

Quote:

Originally Posted by Duke Craig (Post 587859)
Star Classes O B A F G K M,
Remember the Mnemonic: Oh Be A Fine Girl Kiss me.

However, what would be the colour of the sky under the various classes of stars?

(There are also several classes of star below M, including L, T and Y...)

Enjoy!

In that order, no less. L0-9 are the older M10+

Class L is 1300K to 2400K... They're supposed to be capable of deuterium-tritium and deuterium-deuterium fusion, mass wise. I've seen arguments that the cannot sustain protium-protium fusion; If they do, it's slow. Several known brown dwarves have higher surface temps, but those are "hot jupiter" types.

Class T is surfaces of temps 550 and 1,300K . Class T are presumed to exceed 13 MJ, but arguments have been made that sub-13 Mj could be class T5-T9 due to young age. They are considered to be too low for protium fusion.

Class Y is proposed for superjovian bodies that are radiant; such radiance is presumed not to be from Deuterium fusion

note, a few quick googles...
Quote:

Originally Posted by new scientist via Google
The hottest planet yet is twice Jupiter's size and hot as a star. This new exoplanet is too hot to handle. At twice the size of Jupiter and with temperatures reaching 4600 kelvin (over 4300C), KELT-9b is the warmest world ever discovered. Jun 5, 2017

and
Quote:

Originally Posted by Space.com
Astronomers have detected a new candidate for the coldest known star one whose temperature is roughly equivalent to a fresh cup of tea. The object is part of a double system and is a type of star known as a brown dwarf, which is essentially a failed star.Mar 23, 2011

It's about 475K... and is part of a binary pair of brown dwarves.[/quote]

Digging around, Wikipedia lists the coldest normal star (which means fusing protium to some degree) as a class L2.5 V, going under the name 2MASS J0523-1403, with a temp of about 2073K.

Arguments have been made that L3 is about as cool as a star could get; other arguments have been made that, in high metalicity situations, fusion might be interfered with (but not stopped) by "contamination"... but that's not widely accepted from what I can tell.

Duke Craig June 8th, 2018 11:27 PM

Here I found a definitive answer on http://epod.usra.edu/blog/2009/02/sk...exoearths.html

It can be seen that the sky is blue for a star with temperature above 3,300 K; the sky is white near this temperature (as would be the case for star GL 581, where "super-earths" were recently discovered); the sky is yellow, orange and red for temperatures below 3,300K.

Nick Hoekzema planetary astronomer, retired wrote "Thinner atmospheres: The sky gets darker and bluer. Go into the mountains and look up ;-)

Thicker atmospheres: obviously the opposite effect. The sky on a planet with a very thick atmosphere would look like a smoothly clouded sky. Its colour will be the average colour of the star that this planet orbits.

Note that a star has to be very, very red (i.e. cool) before the sky turns red. Also, the scenery on a world around an average M dwarf wouldn't look all red. A colour temperature of 2700 K is still called ‘warm-white’."


Enjoy!

ovka June 9th, 2018 06:20 AM

Nice! I'll be using some of this information. Player's always remember the people and places that are different for one reason or another.

Cheers,

Baron Ovka

shaunhilburn June 19th, 2018 02:26 PM

Quote:

Originally Posted by Duke Craig (Post 587859)
Star Classes O B A F G K M,
Remember the Mnemonic: Oh Be A Fine Girl Kiss me.

However, what would be the colour of the sky under the various classes of stars?

I posted this in an earlier thread on this same topic:
http://www.travellerrpg.com/CotI/Gal...1_SkyColor.jpg

Duke Craig June 21st, 2018 12:53 PM

Quote:

Originally Posted by shaunhilburn (Post 588265)
I posted this in an earlier thread on this same topic:
http://www.travellerrpg.com/CotI/Gal...1_SkyColor.jpg

Thanks for the insight.

Enjoy!


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