39
votes
Can lightning occur in stars like the Sun?
Stars are not actually gaseous, they are plasmas, i.e., highly ionized. Hence, the entire star is highly conductive and does not easily develop the voltage difference via friction needed for lightning ...
- 4,683
14
votes
Accepted
Do brown dwarfs have stripes?
A number of brown dwarfs have had 'surface maps' created using the light from those stars.
In 2013, observations of 2MASS J22282889–4310262, a brown dwarf 35 light years away, were published. These ...
- 1,070
12
votes
Accepted
Does the Sun have any atmosphere?
Yes the Sun has an atmosphere.
Disclaimer: I'm not sure if you meant this, but your question implies the Sun is a planet. It, of course, is a star and not a planet. Just wanted to make that clear.
...
- 15.1k
12
votes
Accepted
A neutron star without a flat surface and an atmosphere?
There is a number of issues with the question, but let me sketch out some kind of answer, so you get something out of it.
The atmosphere of a neutron star is a topic that's a bit speculative. ...
- 18.4k
9
votes
Accepted
At what depth below the Sun's surface does the density reach that of water?
The sun's density is 1 gm/cc at approximately 50% of the way down towards the core. if radius of Sun is R then at R/2 the density will be that of water.
@astrosnapper's comment links to this answer ...
- 4,504
9
votes
Accepted
Can lightning occur in stars like the Sun?
An essential feature of the lightning is the electrical breakdown - an insulator (air) becomes a conductor for a while, relatively high current flows in the conducting channel for a short while, then ...
- 2,879
7
votes
Accepted
Is the gas in a planet forming disk around a star comparable in density to an atmosphere?
The total mass of all the planets is about $3\cdot10^{27} kg$. If you assume the proto-planetary disk to have a radius of $10^9 km$ (somewhat beyond the orbit of Jupiter) and a thickness of $10^7 km$ (...
- 3,611
7
votes
Accepted
Does the Sun's atmosphere have a scale height?
The exponential decrease in density comes out naturally whenever you have a gas in hydrostatic equilibrium. The scale height $H$ is then given by the balance between the kinetic energy of the ...
- 39.6k
7
votes
Accepted
What does this "web on the surface of the Sun" image reflect? What does 789 nm show us?
Well let me take a stab at it. The line in question is said to be a probe of an Fe XI line, that is iron atoms with 10 electrons removed.
You do not get such ions in the solar photosphere, it is far ...
- 162k
6
votes
Accepted
Why are helium resonance lines called "resonance lines"?
It appears to be a conventional label that is applied to transitions between the ground state and another energy level (some definitions specify the first excited level) of an atom and is used in all ...
- 162k
5
votes
Accepted
Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?
According to Formation of the UV Spectrum of Molecular Hydrogen in the Sun (S. A. Jaeggli et al. 2018 ApJ 855 134, also here) molecular hydrogen in the sun was first spectroscopically discovered in ...
- 3,611
4
votes
Accepted
What causes the Balmer Jump?
The Balmer break comes from a combination of two main things: the ability of photons with high enough energies (wavelengths shorter than 364.5 nm) to ionize hydrogen atoms that are in the $n = 2$ ...
- 18.4k
4
votes
Accepted
Wilson effect: How "deep" are sunspots?
Interesting questions! I hope I can shed some sunlight on them.
As stated in the abstract that you quote, understanding and modeling of sunspots is an open question, especially the question how the ...
- 4,553
4
votes
What does this "web on the surface of the Sun" image reflect? What does 789 nm show us?
The Sun is pretty much a blackbody for every purpouse except when looking at it with a rather precise spectrometer.
Then again, it is not a constant temperature blackbody. The brightness of these ...
- 2,879
4
votes
A neutron star without a flat surface and an atmosphere?
The scale height of a neutron star atmosphere is indeed of cm scale.
An isothermal atmosphere will decay as
$$ \rho = \rho_0 \exp( -kT/mgh)\ ,$$
where $\rho$ is the density, $\rho_0$ is the density ...
- 162k
4
votes
Accepted
What was the "optical illusion" that led to erroneous metal concentrations in stellar atmospheres in the galactic center?
The journal paper is Thorsbro et al. (2018).
The facts are somewhat mundane. The atmospheres of cool M-giants are not well understood in detail. The infrared lines of neutral Scandium that had ...
- 162k
3
votes
Accepted
Why does the adiabatic exponent decrease at the ionization zones?
There are two things going on. (1) When you add heat to a gas that is on the threshold of ionisation or partially ionised, some of that heat goes into ionisation. This means that it takes a much ...
- 162k
3
votes
Accepted
What is the density profile within the Sun's photosphere? Which one of these is wrong?
I usually don't answer my own questions, but sometimes when the question itself is called into question I make an exception.
The density of the photosphere at $\tau_{5000}=1$ is predicted to be $3 \...
- 30.7k
2
votes
At what point does an astronomical body's surface stop being gas giant-like and start being sun-like?
A "star" has significant hydrogen fusion occuring in its core. This energy prevents collapse and allows the star to reach a stable position state.
A Brown dwarf does not have significant ...
- 129k
2
votes
What does the opacity of a molecular transition mean?
I know what an optically think/thick medium is...
Okay so this isn't much more complicated. A medium or material can be optically dense or opaque at one wavelength, but fairly transparent at a ...
- 30.7k
2
votes
The sun "burns" hydrogen and even has "campfires" on it, but has anyone calculated a rate of actual chemical burning on the Sun?
I just became curious enough to search a few keyphrases.
This article talks about hydrogen molecules acting as energy "sink" in the sunspots - much like water phase changes on Earth create ...
- 2,879
2
votes
What effect does stellar granulation to have on a chemical analysis of a star's spectrum?
There is no simple answer to these questions - although I could be brief and say
(i) No it doesn't and (ii) no they won't.
If you make a simple two component atmosphere then the observed spectrum will ...
- 162k
2
votes
Accepted
Would the electron cyclotron-maser emission mechanism affect Proxima b's ability to retain an atmosphere?
This mechanism, being actively emitting in the radio-wavelengths, is certainly negligible for the overall atmospheric energetics at Proxima b. One can conclude this by taking the band luminosities ...
- 9,869
1
vote
Why are helium resonance lines called "resonance lines"?
I can not assure that this terminology is different in other fields than in solar physics, but when a line is called to be "resonant" is because the lower level of the transition is the ...
- 11
1
vote
Does the Sun's atmosphere have a scale height?
It does not come out quite clearly from the accepted answer that the underlying reason for an exponential height decrease of the atmospheric density is the fact that in thermodynamic equilibrium the ...
- 3,611
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