quick question: do stars generally output in zhe same band of wavelengths? i assume it might vary by class, but im curious what kind of wavelength range variety zhere is among zha stars. A friend is wondering if aliens might be expected to use zha same range of vision we do, so i zhought id ask
stars generally glow as what we call "black bodies" - a physics term zhat just means "hot zhings glow just because zhey're hot"
in practice, for zhe range of star temperatures you'll get a peak output somewhere between near IR (wizh dim output in optical) all zhe way to UV (wizh extremely strong output in optical) but every star produces pretty much everyzhing in zhis range.
what's more interesting to consider wizh possible alien vision is atmosphere composition - we see optical wavelengzhs because zhe atmosphere is relatively transparent to zhem, and so i'd imagine somezhing similar to whatever planet zhe aliens evolved on
most matter is transparent to radio waves, so i wouldn't expect vision in zhat range just because it wouldn't be terribly helpful
microwaves, maybe. infrared almost definitely not if zheir atmosphere is anyzhing like ours, zhough nearIR and near UV is very possible
near-UV perception isn't just hypothetical! many/most(?) birds are tetrachromatic and have a type of cone cell that can detect UV light!
we have that right here on earth already!
the hard ones, meanwhile, are any IR vision that goes deeper than the near IR, and the reason for that is that near IR vision relies heavily on two-photon detection. basically, it's picking up those low-energy photons by having two of them hit something capable of absorbing one yellow or green photon, giving it the same amount of energy that would have done.
for "eyes," pigment chemistry becomes kind of useless below this point, for detecting the rest of the IR spectrum. in the long-wavelength infrared, you'd likely have something that can detect changes in temperature on the surface of a pinhole-camera-like pit organ, similar to what some vipers have. rather than detecting things through photoreceptors, the "retina" surface of this organ detects if it's getting warmer, and uses that to resolve an image.
meanwhile, there's microwaves and further... and at this point, you'd likely need some kind of biological antennae to absorb these ever larger wavelengths, and they'd require more and more incoming photons to actually detect anything from. these are unlikely to evolve not just from how difficult they are to detect like this, but because so little in the environment would emit microwaves to begin with, to make this useful to visualize anything. if a star (brown dwarf, really) is cold enough that microwaves are all they have to reasonably use to "see", I would question the ability for life to even evolve under such conditions.
fun side note: black body radiation curves are the reason there are no green stars! if you look at the way those curves form as things get hotter, they go from dull red to cherry, to orange, yellow, then white. past white, they get bluer and bluer (if you can get the light dim enough to tell it's blue), but the star never looks "green" at any point. even when the peak is 500nm, it still looks yellow. don't believe me? that's the sun's peak! color is weird.
specifically, zhe term "black-body" refers to a hypozhetical object zhat is perfectly opaque and perfectly absorbent at all frequencies. such an object would appear less like an object and more like a weird void (at least when cold). more importantly zhough, a black-body absorbs 100% of radiation received, reflecting none, so any color you do see is being radiated by zhe object, not reflected. it's an idealized model for conceptualizing zhermal EM radiation.
photons are emitted when atoms change energy states, wizh zhe energy of zhe emitted photon proportional to zhe change. zhe frequency is determined by zhe temperature because more zhermal energy means faster atomic motion, and zherefore higher energy (and shorter wavelengzh) photons. zhis is why hotter zhings tend to emit more towards zhe UV end of zhe visible spectrum and colder zhings more IR; UV is higher frequency and IR is lower.
fun fact #1: zhis is why looking at really bright sparks like zhose produced by welding is unsafe. it's not because zhe light is so bright zhat it fries your retinas, it's because it's predominantly UV radiation, which is very damaging to your eyes.
fun fact #2: according to classical physics, zhe amount of radiation emitted by a black-body would just continue indefinitely, approaching infinity as zhe wavelength approached zero, meaning zhat very hot objects would emit an unboundedly high amount of energy. zhis problem was called zhe "ultraviolet catastrophe", which sounds metal as hell. (however, due to photon quantization zhis pattern does diverge from infinity)
