Ambient Light

[ovka]

So, my recent thread about stellar data got me studying and thinking. Do the different stellar classes produce a noticeably different color of ambient light on the worlds that orbit them? Would a type O or B star give a slight twilight-hue to the landscape? Would a type M star give a reddish-hue? Would this only extend out to a certain orbit?

I'm just trying to think of other ways to describe various worlds and systems to make each somewhat unique so that they stick out in players' minds. ("No, Aramis was the desert world with the bad atmosphere and the underground city. Lablon was the agricultural world where the sky always glowed red, and it took us a over a week to get in from the 100D limit."

Cheers,

Baron Ovka

 

[JCStephens]

I expect the planet's atmosphere would have more of an effect than the stellar class. Look at the photos of Mars; same star but different air.

On a related note: is there a method for determining brightness on a given world? At what point would the low light level affect sighting distance and combat DMs? I have an idea that luminosity and orbital position would be involved, has anyone else done any work on this?

 

[whulorigan]

So, my recent thread about stellar data got me studying and thinking. Do the different stellar classes produce a noticeably different color of ambient light on the worlds that orbit them? Would a type O or B star give a slight twilight-hue to the landscape? Would a type M star give a reddish-hue? Would this only extend out to a certain orbit?

I'm just trying to think of other ways to describe various worlds and systems to make each somewhat unique so that they stick out in players' minds. ("No, Aramis was the desert world with the bad atmosphere and the underground city. Lablon was the agricultural world where the sky always glowed red, and it took us a over a week to get in from the 100D limit."

Part of the visual experience from a world surface would also depend highly on the chemical composition of the atmosphere (perhaps at higher levels), as certain elements and compounds will absorb certain wavelengths of light and alter the appearance of the sunlight, as will particulate filtering.

Sol (as a G2 V) is fairly close to "white" in color, but looks yellow from Earth due to atmospheric filtering & absorption. The traditional "colors" associated with OBAFGKM are those as seen by historical astronomers using ground-based telescopes, meaning that the apparent colors are those as seen thru Earth's atmosphere.

A rough breakdown of the approximate colors as seen in vacuum based on spectral type (which is based roughly on photosphere temperature) :

[FONT=arial,helvetica]Spectral Classification

O - Blue
B - Blue/Blue-White
A - Blue-White
F - White
G - Yellow-White (traditionally called "yellow")
K - Yellow/Yellow-Orange (traditionally called "orange")
M - Pink-Orange (traditionally called "red")

L - Orange-Red
T - Cherise/Magenta
Y - (Infra-Red)[/FONT]

To human eyes, of course, the light will almost always look "white" due to brightness/saturation, but the "tinge" or "shade" of color cast on the landscape (after absorption/filtering is accounted for) ought to be noticeable.

 

[tjoneslo]

So, my recent thread about stellar data got me studying and thinking. Do the different stellar classes produce a noticeably different color of ambient light on the worlds that orbit them? Would a type O or B star give a slight twilight-hue to the landscape? Would a type M star give a reddish-hue? Would this only extend out to a certain orbit?

I've been using the Star Color page to get a more accurate set of colors for the star's in a vacuum. The star colors (red, blue, white, etc) are astronomer derived shorthand for "color in relation to Vega, the brightest star we know".

I've seen pictures, but can no longer find them, of people having redone an image from earth, but with the spectrum from various different types of stars. The images were not much different. The color of light emitted across the visible spectrum by most stars, especially the main sequence stars, isn't widely different.

For people (like Traveller characters), used to traveling to different stars may not even notice much of a difference. Like whulorigan says, the large difference may be in the atmosphere. Taints will always produce different colors in the sky.

Other things that may make the world more memorable:

* Moons. Does the world have one large (ish) moon, several small ones, or a ring?
* Is the world a satellite of a gas giant. There are a number of these in canon, and describing the banded gas giant overhead would be interesting.
* Stellar flares. M class stars are prone to them, and they can be brighter than the star itself (and really dangerous).
* Flares also would cause Aurora's on worlds with a magnetic field.
* Comets are always good, visible both in space and from the planet surface. Especially if the comet is being used as part of a terraforming effort. Terraforming requires water, comets are water, so they may be moving one into close orbit around a world to water it.

 

[warwizard]

https://en.wikipedia.org/wiki/Black-body_radiation vs spectra output curve
as temperature rises so does the peak emission frequency, however the frequencies emitted at all the lower temperatures are there as well and never get smaller it's just there is more of everything.

So let's go through the spectra: http://www.ezizka.net/astronomy/lessons/topicslesson08/topic01lesson08.htm
O Peak emission in the far UV plenty of light for you to see at the lower frequencies, though you'll not be seeing it for long as the far UV destroys your eyes in short order. No carbon based life exposed to solar radiation as the UV breaks the carbon-carbon bonds.

B Peak emission in near UV it will still destroy your vision, just not as fast. Enough far UV is still produced to destroy carbon based life though if the star wasn't only a few tens of millions of years old you could perhaps have some xenophobes evolving

A Peak emission "blue" need UV protection to prevent damage to eyesight in 3-4 months. Locally evolved carbon based life is unlikely, not enough time. Imported species would be geeneered for UV resistance and would appear deep blue to blackish depending on the local spectra

F Peak emission "light blue" You will need UV protection to prevent eyesight loss in 3 years or so. Local plants will be UV hearty and appear blue to bluegreen depending on the exact local spectra.

G Peak emission is "green" Sol is of this spectral class still need UV protection for your eyes to prevent damage on a scale of 30 to 40 years

K Peak emissions is "orange" The Kizinti are evolved at a K spectral class sun, local plants appear orange as the plants absorb the orange and reflect the rest.

M Peak emissions is "red" UV will mostly be absent, however if there is an accretion disk you will have X-ray bursts as the magnetic field uncoils from the accretion disk. This is repeated as the disk continually winds up the magnetic field. With accretion disk this is an unhealthy place for carbon based life. Other wise local plants will evolve for the red color light and will appear various shades of red according to the exact local spectra.

Brown dwarf (3 spectral classes) Here you will have peak emissions in the far IR, there will not be enough visible light to activate your eye's color sense so everything would appear in shades of grey. You will feel the IR on your skin, local plants would appear black.

 

[Enoki]

I'd add to "memorable" details things like:

The size and proximity of nearby planets. These might be visible even in daytime if they're bright enough. The world orbiting a gas giant that takes up the entire sky would be rather spectacular.

Color of moons. This can be due to a combination of light and the moon's composition. For example, you might have moon with a distinct color of rock making up most of it. Or, it could be ice or water covered, giving you a true "Blue moon."

Cloud color: A combination of the atmosphere and sun could cause these to be pink, green, brown, or some other color rather than white.

The size of the primary star: A giant star might look several times larger than ours does in the sky. For cooler M stars it might dominate the entire sky in its direction.

Rotation of the planet. The sun rises in the north and sets in the south, or some other variant of that. Tidally locked planets could be another situation. I recall a science fiction series (can't remember the name) where the planet was tidally locked and there were floating "satellites" in the sky...

 

[agorski]

I'm just trying to think of other ways to describe various worlds and systems to make each somewhat unique so that they stick out in players' minds.

I would think the vegetation would be a different color. Black with an M star?

 

[shaunhilburn]

So, my recent thread about stellar data got me studying and thinking. Do the different stellar classes produce a noticeably different color of ambient light on the worlds that orbit them? Would a type O or B star give a slight twilight-hue to the landscape? Would a type M star give a reddish-hue? Would this only extend out to a certain orbit?

Imagine the differences between "soft white" or "warm white", "cool white", and "daylight" lighting products sold at home improvement stores. They usually have displays set up to illustrate the lighting differences. That same range of hues is found in stars.

A red star produces illumination comparable to an incandescent lamp, or "warm white". The hue of outdoor illumination in an earthlike atmosphere depends on exactly how "red" the spectrum is. The rays of an M7 dwarf (2,600 K) will appear like those of our own setting sun regardless of the actual illumination angle. The sky is a sort of dark "warm gray", and the clouds have the ochre and "peach" tones of late day.
https://en.wikipedia.org/wiki/Golden_hour_(photography)

An M0 dwarf (3,800 K) will to have a more full spectrum white, similar to a 4,000 kelvin "cool white" source.


A common misconception is that red suns will appear even more red near the horizon. Not so. Any sun near the horizon will yield a scene that is recognizably similar to our own sunrises and sunsets on earth when seen through an earthlike atmosphere, with minor hue changes to the the solar disc and the sky immediately surrounding it.

I'm just trying to think of other ways to describe various worlds and systems to make each somewhat unique so that they stick out in players' minds. ("No, Aramis was the desert world with the bad atmosphere and the underground city. Lablon was the agricultural world where the sky always glowed red, and it took us a over a week to get in from the 100D limit."

Years ago, I had done some test renders with Terragen 2 to satisfy my own curiosity on this topic. Terragen 2 has a realistic sunlight penetration and rayleigh scattering algorithm.

It appears that the most unearthly scenes are produced by suns at the bottom of the main sequence, e.g. M7V and below, and the illumination becomes progressively more familiar as you work your way up to spectral class K2. There doesn't appear to be much change in the color of sky and clouds after that no matter what the sun temperature is dialed up to.

I wish someone could tell me how to post these images to the forum.

 

[77topaz]

I wish someone could tell me how to post these images to the forum.

You can upload images at this page.

 

[shaunhilburn]

You can upload images at this page.

Here they are:
http://www.travellerrpg.com/CotI/Gallery/images/4003/1_SkyColor.jpg


Outdoor scene illumination with a hyopthetical adjustable sun. These swatches were done to compare the changes as the spectral class is adjusted up or down. They were done in 2008. I chose Terragen 2 because for the amazing realism of its atmospheric model.

 

[aramis]

https://en.wikipedia.org/wiki/Black-body_radiation vs spectra output curve
as temperature rises so does the peak emission frequency, however the frequencies emitted at all the lower temperatures are there as well and never get smaller it's just there is more of everything.

Snipped a bunch of good discussion... but remember: natural atmosphere provides a LOT of potential for UV absorption.

Otherwise, we'd all be blind.

 

[warwizard]

Granted, but with an order of mag more UV as each younger spectral class is considered, I was thinking even a 99 % filter will not help against the class O.

You would have to build your agri-domes on planets or orbitals at A or younger spectral class stars with materials that are 100% opaque to Far UV and absorb the near UV by 99.99%. In fact chemical compounds of any type have their chemical bonds broken by the far UV. This is why scientists tell us that any captured planet at a class O star would have meters of fine dust, water would not exist on the surface as the light cracks the water and the hydrogen escapes. Class O stars do not live long enough for planets to form, their solar intensity is such that the proto star's accretion disk and planetary nebula are totally disrupted and the mass blown past the dew line. (dew line is where water condenses on surfaces in vacuum and the solar infusion is insufficient to sublime it faster than it deposits) I'm unsure if a class O even has a dew line, if it did it would be WAY far out like a half LY or more, it would be better to characterize it as an elemental asteroid line, rock asteroid line or some such nomenclature.

 

[77topaz]

I think any system around a Class B or especially a Class O star would probably have to have an asteroid belt as the mainworld (that's the approach I've taken with the Orion OB1 Association, anyway).