if one day we will find life in the oceans of enceladus and europa and the life there will be organic fish like on earth....would they be edible? hypothetical speaking....

Spacer, no need to hide yourself.  We all know you crave to eat aliens.
If the biochemistry is similar then yeah, they might be edible.  On the other hand, we might also be edible to them...

Didn't NASA issue a report today of finding life-precursor compounds on Enceladus?

The more we find organic compounds out there, the less I am surprised.  Seems like they're extremely common, with a lot of ways for them to be created in different astrophysical environments.  The real question is how and where it takes the next steps to becoming living structures.

What if Jupiter Formed in Saturn's place, and Saturn formed in Jupiters place? 

The best answer is probably one given in terms of probabilities, because the way the solar system evolves early on is very dynamic and chaotic.  This situation could definitely lead to very dramatic differences from how the solar system appears today.

Spacer- that reminds me of Isaac Asimov.  Weren't spacers genetically modified humans with extended lifespans who were the first colonists and later superseded by the Settlers?

I was reading about William Herschel the astronomer, and he believed that it was only Earths atmosphere that made the stars, planets and even the Sun visible from Earth, and that outside of an atmosphere of sufficient density and composition, nothing is visible, and that even the heat we feel is generated by the atmosphere.

Never heard that before -- if it's true that's pretty interesting.  

Of course, Herschel lived ~200 years ago.  Today we have a robust theory of electromagnetism, Maxwell's equations, and an understanding that light propagates through a vacuum unimpeded.  Indeed, you can say that the vacuum is the most natural medium for light to propagate in.

So understanding the appearance of stars and our Sun from outside of the atmosphere is actually pretty simple, and there are abundant space-based observations to go from.  You can find photographs containing the Sun from Apollo missions, the Shuttle and ISS footage, as well as images specifically intended to study the Sun from dedicated observational platforms like SOHO.

Visually, the Sun from outside the atmosphere looks like a blindingly bright white orb, and similarly in photographs.  A photograph exposed to capture details on its surface will reveal sunspots, and in other wavelengths other details of the solar atmosphere become apparent.
The effect of the atmosphere is to dim and redden the light by absorption and scattering, and the atmosphere also refracts the light slightly (you can actually still see the Sun when it is geometrically below the horizon, which is pretty neat).

SE model of the Sun is based on algorithms mimicking as much as possible visuals and mathematical simulations based on stellar evolution theories.

Basically yes.  All important properties of a star are determined by their initial mass and age, so SE uses results of stellar evolution models to determine their appearance.  The color and brightness is based on the physics of a blackbody spectrum (color and brightness are a function of temperature, with hotter surfaces being brighter and peaking in shorter wavelengths).

I thought the sun was yellow  In any star class diagram I've looked at and H-R diagram, they describe G-class stars as yellow and A-class stars like Sirius as white. It is an issue for when I take pictures about how to set the white balance.  
If any alien species exist around stars of different spectral types, their stars should appear to be white to them- regardless of how they appear to us.

or die from alien desease (like a flu, war of the worlds...) our planet never seen....

That is highly unlikely.  Any microbes they have will have evolved in a completely different environment and not be compatible.  We see this all the time here on Earth with diseases that only infect certain species and we all evolved on the same planet.

Funny thing is, I see researchers wearing masks when they work with chimpanzees.  I guess we are too closely related to them and there is a risk of disease transmittal there.

Will alien chirality provide any obstacles

As far as I remember chemistry, could be. In terms of food, chiral compounds (let's say a complex protein and it's three-dimensional mirror image, so-called tertiary structure) even on Earth can greatly differ in how are adsorbed and digested in single amino acids when eaten.
Let's put this in another planet, where fundamental structures of life like DNA could be even not necessarily based on thymine, adenosine, guanine and cytosine and the other one I don't remember used in RNA, but instead made by five or six similar compounds at the same time, well this could very possibly lead to some memorable stomach ache.

Or if we ever find an alien which is composed of arsenic

Something interesting that I was reading was how different total solar eclipses and their effects appear in person vs what you can capture with a camera- mainly because our eyes are much more sensitive to changes in light than a camera is.

If you have seen the latest PBS Space Time video, (which I have posted over in Science and Astronomy Videos) you may also be asking yourself the question of the source of these high-energy particles. I thought about this and here's my hypothesis: The source of these particles isn't visible because it's source is made mostly of dark matter/energy. Couldn't it be possible that dark energy fields would have the same effect on protons as normal energy fields have on electrons? What do you guys think?

I thought the sun was yellow

There are many ways to define its color.  We can indeed consider it a "yellow" star by its spectral type.  Its peak wavelength (the part of the spectrum where it is brightest, by Wien's Law) is green.  And to our eyes it is white because our vision evolved to interpret sunlight that way.  Similarly the sun's "color temperature" in the color space of cameras and computer graphics is also nearly white:

It is a forward scatter process of UV/EUV light from the Sun that creates a beam of visible light that we see from Earth, so the atmosphere is acting as a kind of optical transformer.

Never heard this before either.  How or where did you come by this idea?  

It seems to me that your idea predicts that the intensity of visible illumination on an object would be a function of altitude, decreasing in relation to the atmosphere's scale height.  Is this what we observe?  Your idea also predicts that all space-based astronomy is useless, because the stars would be invisible.  So not only must NASA be in on the conspiracy, but every space agency, and every astronomer and astrophysicist.

It's cool to share your ideas but I think you should know that the phenomena you are interested in are well explained by the theory of electromagnetism and interaction of light with matter, which you can learn about in any university physics program.  This is the right thread to discuss things like that, but if you prefer rejecting physics in favor of conspiracy-theorist thinking then it belongs in a different thread.

Lol I hope the idea of the sun being (slightly) yellow doesn't fall into the area of conspiracy theory my friend

Most cameras set sunlight white balance to somewhere around 5300K while the surface of the sun is around 5800K so they are actually making the sun seem slightly bluish for some reason.  I contend that it should be slightly yellowish so the sunlight white balance temperature should be around 6500K (which is close to where an A-type star would be white, since that is the surface temp of a star like Sirius.)

Unfortunately with all these orange-yellow sodium and mercury lamps causing light pollution issues, the camera's auto white balance often corrects too much towards blue and sets white balance to somewhere between 3200K and 4000K and then EVERY star but really red stars like Betelgeuse appear to be blue.  I have to set WB myself and then the skies look a really yucky orange color- but at least the star colors are right.

I remember looking up why no stars were green or purple once- something about stars that peak in the green area also have a large quantity of other colors in their spectrum too? (Although the companion to Antares as well as a star in Libra appear to be green by optical illusion.  About the lack of purple stars I don't know- I used to think Wolf-Rayet stars were purple.)

Heard on the news tonight about an earthlike planet being found that is 7x the size of Earth? We won't know if it has any oxygen in its atmosphere until the next exoplanet satellite launch.

lhs l40b 40 ly away

Lol I hope the idea of the sun being (slightly) yellow doesn't fall into the area of conspiracy theory my friend

Lol, goodness no.  The conspiracy theory comments were in response to GaryN.  

I remember looking up why no stars were green or purple once- something about stars that peak in the green area also have a large quantity of other colors in their spectrum too?

That is a part of it.  Stars emit a blackbody spectrum, whose peak wavelength is a function of temperature.  The sun peaks in green but it also gives off all the other colors, and our eyes integrate it as white.

Hotter stars may peak in blue, violet, or even ultraviolet, and in all cases they still give off all the other visible colors with decreasing intensity.  But to our eyes these combinations of colors trends toward blue more than purple.  You can see this with the graphic posted above -- the curve in color space traces out the perceived color of a blackbody emitter as a function of temperature. 


The reason for this is that our eyes are not equally sensitive to all colors.  We're vastly more sensitive to green light than to purple -- in fact the sensitivity drops off very quickly as you move to either side of green.  So even if there is more violet light in a very hot spectrum, the blue and green light weighs in more to what our eyes interpret.

This unequal sensitivity of our eyes to different colors is a neat thing to demonstrate, and you can do so if you have lasers of different color but equal power output.  I have a 405nm (violet and very close to ultraviolet) laser, and a green (532nm) laser, both of ~120mW, but the violet one appears much fainter -- even to the point that it doesn't appear dangerous, yet it is intense enough to be felt against bare skin.

Lol I hope the idea of the sun being (slightly) yellow doesn't fall into the area of conspiracy theory my friend

Lol, goodness no.  The conspiracy theory comments were in response to GaryN.  

I remember looking up why no stars were green or purple once- something about stars that peak in the green area also have a large quantity of other colors in their spectrum too?

That is a part of it.  Stars emit a blackbody spectrum, whose peak wavelength is a function of temperature.  The sun peaks in green but it also gives off lots of other colors, which our eyes integrate as white.

Hotter stars may peak in blue, violet, or even ultraviolet, but in all cases they still give off all the other visible colors in decreasing amounts, and to our eyes the combination of colors trends toward blue more than purple.  You can see this with the graphic posted above -- the curve in color space traces out the perceived color of a blackbody emitter as a function of temperature. 


The reason for this is that our eyes are not equally sensitive to all colors.  We're vastly more sensitive to green light than to purple -- in fact the sensitivity drops off very quickly as you move to either side of green.  So even if there is more violet light in a very hot spectrum, the blue and green light weighs in more to what our eyes interpret.

This unequal sensitivity of our eyes to different colors is a neat thing to demonstrate, and you can do so if you have lasers of different color but equal power output.  I have a 405nm (violet and very close to ultraviolet) laser, and a green (532nm) laser, both of ~120mW, but the violet one appears much fainter -- even to the point that it doesn't appear dangerous, yet it is intense enough to be felt against bare skin.

I know, I just thought it would be rather funny if someone created a conspiracy theory based on the sun being a radically different color than what billions of people know it to be- let's say someone said that the sun was really purple with pink polka dots lol.
Agh, you are so lucky!  I wanted to do an experiment but not sure it can be done.  I have chandeliers that act like prisms and create rainbows on my walls (and on my TV- where the colors appear particularly contrasty because the screen is black when turned off.)  I know that camera sensors can detect colors we cannot- more on the infrared end of the spectrum, but also on the ultraviolet end.  I was thinking of using both a UV403 filter and an IR720 filter to filter out visible light and see if I can detect the "invisible" parts of the rainbow with the camera.  Not sure if it's possible because cameras have blocking filters on them.  I can do IR photography- but the camera's blocking filter removes about 8 stops of IR light, and on the other end of the spectrum, about 13 stops of UV light.  I do get that neat phosphorescent effect with green foliage though and those amazingly contrasty sky colors.  By the way this same blocking filter is a bit of an inhibitor when it comes to astrophotography of H-alpha emission nebulae, which radiate mostly in the far red end of the spectrum.
This color stuff is really interesting and I researched it for a long time.  Some of the amazing things I found out is that although most of us humans have three types of cones to detect color (thus three primary colors), some lucky people have a fourth type of cone (four primary colors!) so they can actually see more color than normal people can?  And who said that superhumans didn't exist
There are some people who only have two types of cones and they see less color and have color blindness (the most common type of which is red-green- which unfortunately are the colors of our traffic lights) but there are now glasses to correct for that.
On the other end, there are some rather amazing crustaceans that have up to 13 types of cones- who knows how many colors THEY can see!  Some of these are rather intelligent squid who can also change color depending upon their emotions.
Another species that can see colors we can't are bees and other pollinators- what's fascinating here is that flowers that want to attract them display hidden patterns on their petals that can only be seen in the UV range which these bees can see and we cannot.  But with that UV403 filter we can actually capture these hidden patterns of invisible light with our cameras  Just have to use a tripod because of that blocking filter.

I was told not to do UV photography of any bright UV sources because the energy of the UV rays will start to fade the camera's Bayer color filter array- similar to how sunlight can make furniture and wall colors start to fade.

And then there is the whole topic of "Imaginary colors"- colors which technically should not be possible but some people still report being able to see them (perhaps these are the people with the extra types of cones?)  

I was thinking of using both a UV403 filter and an IR720 filter to filter out visible light and see if I can detect the "invisible" parts of the rainbow with the camera.  Not sure if it's possible because cameras have blocking filters on them.  I can do IR photography- but the camera's blocking filter removes about 8 stops of IR light, and on the other end of the spectrum, about 13 stops of UV light.

Yeah, that's a pretty big reduction, but I guess that means the filters are doing their intended job.  There are some guides online for how to modify the camera with taking the filters out, but it's probably not something you want to try unless you are really serious about it and have equipment to spare.  If you're managing to get some results with the filter in place then that's pretty awesome.  I really enjoy looking at B&W infrared photography -- it gives an amazing way to see the world and can produce some really interesting art.  People's faces in particular are very strange in IR, and landscapes and foliage are neat too.

I'd love to see some shots you have made!

Some of the amazing things I found out is that although most of us humans have three types of cones to detect color (thus three primary colors), some lucky people have a fourth type of cone (four primary colors!) so they can actually see more color than normal people can?  And who said that superhumans didn't exist

I've heard of this and it does sound pretty interesting.  And there are other superhuman senses as well.  I had the privilege to meet a "supertaster" who puts that skill to use as the blendmaster of a tea company.  People also generally have a broader range of hearing when they are young, and lose the sensitivity to high frequencies as they age.  I used to be very sensitive to higher frequencies than normal, and have a vivid memory of walking through a neighbors yard with some friends and was suddenly incapacitated by a soul-piercing sound that nobody else could hear.  Turns out we had walked in front of a motion-sensitive deer deterrent that throws out ultrasound.

This gets more into the realm of neuroscience than color theory, but have you ever heard of a condition called hemineglect?  I think it's one of the weirdest things about how people can perceive the world differently.

A-hem. I assumed nobody saw it since it was towards the bottom of the page

Hornblower, The origin of the highest energy cosmic rays, and why we observe as many as we do despite the expectation that the CMB would apply an important breaking effect to them, is a significant unresolved problem in astrophysics. Dark energy is also pretty darn mysterious, but I'm doubtful that there is any important connection between the two.  

When modeled as a cosmological constant, dark energy is a type of gravitational field (more generally, a correction to the metric of space-time) and so it affects all particles equivalently.

Dark energy also can't accelerate particles in a particular direction.  Intuitively one would think dark energy would expand the universe by "pushing out" on things, but that's actually not how it works -- in cosmology it can't work that way because there is no preferred direction to push from and no walls to push against.  The dark energy is uniform and so it does not apply a net force on anything.   Instead, it affects the expansion of space itself because of its energy density, which changes the metric of space-time.

I've moved the nonsense about stars in space supposedly being invisible to the Conspiracy Thread.  The conversation can be continued there.

We have our own X-files thread?! I loved that show- and some of what they talked about was eventually proven true (like mass surveillance)- and some events were taken right out of history (like Operation Paperclip, the Tuskeegee Experiments, and using children in third world countries as guinea pigs for lab experiments.)  Of course, they never did anything as nonsensical as stars in space being invisible haha.  The only stuff they did about space involved the Apollo astronauts seeing UFOs up in space (which was true, but might be attributed to optical effects, and I say MIGHT )