Gas giants like Jupiter and Saturn have bands of different colors in their atmosphere. These are due to the rotation of the planets. Stars rotate too, so why do most stars have patches/blotches of color rather than having latitudinal stripes?
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$\begingroup$ relevant astronomy.stackexchange.com/questions/39410/… $\endgroup$– James KJan 12, 2021 at 19:24
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9$\begingroup$ The bands on Jupiter and Saturn are caused by the rotation but the colors are caused by the atmospheric composition. Stars do have different colors, but this is caused by the different temperature for 2-3000 K for red dwarfs to 30,000+K for blue supergiants $\endgroup$– astrosnapperJan 12, 2021 at 19:26
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6$\begingroup$ Also, gas giants' appearance is due to reflected light, whereas the light of stars is due to their own radiation. Reflected light tends to vary more with material composition than does the blackbody radiation that comes off a hot object like a star. $\endgroup$– Kristoffer SjööJan 12, 2021 at 21:22
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$\begingroup$ The Astronomer's Periodic Table of Elements $\endgroup$– MazuraJan 14, 2021 at 2:08
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1$\begingroup$ I think it's premature to ask this on account of our limited ability to get high-resolution full-spectrum images of any star other than our own. $\endgroup$– Mark Morgan LloydJan 14, 2021 at 14:59
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3 Answers
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Just rotation is the wrong tree to bark up on.
You see color variations on gas giants due to differences in composition, i.e. ammonia vs. sulfuric acid clouds on Jupiter, which are transported differently on the rotating planet in the up/downwelling bands.
Spots on stars originate due to very different physics. At the temperatures which are prevalent on stellar surfaces, molecules are mostly dissociated and ionized, we call this state a plasma, so no more colour effects due to ammonia or others. Star spots are concentrations of the local magnetic field, which is coupled to the plasma dynamics. The magnetic field pushes the gas aside and lets the surface cool locally. This makes dark spots that you see on stars like our sun.
There is a transition region in terms of surface temperature of 2000-3000K, at the masses of brown dwarves. Those failed stars seem to exhibit dark bands on their surfaces, which are thought to be due to absorption from exotic, high-temperature molecules like TiO and VO (Titanium and Vanadium oxide).
answered Jan 12, 2021 at 21:21
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$\begingroup$ Great answer +1 In short, the laws of coloring for stars are governed by temperature, not composition. $\endgroup$ Jan 13, 2021 at 0:54
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$\begingroup$ Can you clarify this sentence "Star spots are concentrations of the local magnetic field, which is coupled to the plasma dynamics, pushes it aside and lets the surface cool locally."? It's not grammatically correct at the moment so I can't parse exactly what it is trying to say. $\endgroup$– TylerHJan 13, 2021 at 16:43
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$\begingroup$ @TylerH: Star spots are concentrations of the local magnetic field, which is coupled to the plasma dynamics. The magnetic field pushes the gas aside and lets the surface cool locally. $\endgroup$ Jan 13, 2021 at 18:48
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$\begingroup$ Can you clarify what you mean by "pushes the gas aside"? That doesn't match my understanding of how sunspots work. (But then, my understanding is that it's still not a well understood phenomenon.) Apart from that sentence, I think this is an excellent answer. $\endgroup$– craqJan 14, 2021 at 20:31
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$\begingroup$ @craq: That depends on which level of detail you're asking about. The basic physics of sunspots is very well understood. Their coupling to the global magnetic field, particularly for stars other than the sun is still in active research. The magnetic field usually follows the plasma flow (frozen-in property of MHD plasmas), but nonetheless slowly diffuses and 'bubbles up' relative to the gas. Once the magnetic energy is sufficiently concentrated in a region, it acts as additional pressure in the Navier-Stokes equation, i.e. the total pressure gradient becomes $\nabla(P+B^2/2\mu_0)$. $\endgroup$ Jan 14, 2021 at 23:00
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The atoms in stars have disassociated electrons at random distances, they are ionised, and the energy converted to light is at a continuous spectrum of wavelegnths and colors.
The heaviest elements with a potential for color fall into the star.
Color bands from stars come from colder atoms in the high corona, which can cool and have fixed electron orbits which output fixed wavelengths.
To have colored stars you would need an elemental veil cloud that acts as a color screen.
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$\begingroup$ The heaviest elements do not sink in a star like the Sun. The Corona is hot, it doesn't contain cold atoms, or atoms at all $\endgroup$– ProfRobJan 14, 2021 at 23:26
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Gas giants don't emit radiation, they reflect it. Due to their mixed composition, there is different amounts of light absorbed in different ways, giving them their distinct colours.
Stars on the other hand glow because of the energy that is produced at their core, and their composition is almost purely hydrogen.
So because of their high temperature, and almost completely or composition, stars glow in just one colour, while gas giants have distinct colour combinations.
While stars don't exactly glow in just one colour, they emit radiation in a predictable manner (according to Wein's displacement formula) which gives the relationship between the temperature and the wavelength of the most emitted radiation
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$\begingroup$ what brand of deoderant? $\endgroup$ Jan 14, 2021 at 8:32
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$\begingroup$ @BillyC. Sorry, I was in a hurry, that I didn't notice the multiple typos $\endgroup$– SK DashJan 14, 2021 at 9:48
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