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PaulLogan
2011-Jun-02, 02:26 PM
i was looking at this stunning picture of the surface of our sun:
http://fettss.arc.nasa.gov/collection/details/sun-sunspots-2/

obviously, the black areas are sunspots but i was wondering about the (in this pic) golden pebble-like structures surrounding them.
what are they made of?
i did a search of course and this site came up - http://www.the**surfaceofthesun.com/ - which has some info but i was wondering if somebody here has more recent info.

thanks!

Shaula
2011-Jun-02, 02:45 PM
Convection cells. Upwelling in the middle (bright bit) and downwelling at the edges. They are called Granules if you want to read more on them.

PaulLogan
2011-Jun-02, 02:51 PM
thanks.

i just saw that the site i quoted seems to be a eu site. i am NOT a eu supporter (i don't even know enough about that theory). it was an honest mistake. i clicked one of the first links and - at first glance - it seemed to contain useful info...

Shaula
2011-Jun-02, 03:21 PM
I hadn't really looked at the site to be honest! This page (http://solarscience.msfc.nasa.gov/feature1.shtml) has some more information on the different features you see and how they organise. This one (http://spacescience.spaceref.com/newhome/headlines/ast28may98_1.htm) is old but has some basics on how these cells organise.

Swift
2011-Jun-02, 03:23 PM
Convection cells. Upwelling in the middle (bright bit) and downwelling at the edges. They are called Granules if you want to read more on them.
A mediocre analogy - think of it as the surface of a simmering pot of liquid, you have convection cells of hot liquid rising from the bottom of the pot.

phunk
2011-Jun-02, 03:49 PM
what are they made of?

Everything in that picture is made of the same stuff (mostly hydrogen). It's just at different temperatures and moving in different directions.

Even those 'black' areas aren't really black, they are actually very very bright. They only appear black when the image exposure is set to see the details of the rest of the surface.

Van Rijn
2011-Jun-02, 07:57 PM
i did a search of course and this site came up - http://www.the**surfaceofthesun.com/ - which has some info but i was wondering if somebody here has more recent info.

thanks!



That is an extreme ATM site. That is by Michael Mozina, a fellow we had here before, who claimed the surface of the sun was solid, which doesn't make sense for many reasons.




i just saw that the site i quoted seems to be a eu site. i am NOT a eu supporter (i don't even know enough about that theory). it was an honest mistake. i clicked one of the first links and - at first glance - it seemed to contain useful info...

Fair enough, but I still want to clarify for others that might see that link.

John Jaksich
2011-Jun-02, 08:58 PM
That is an extreme ATM site. That is by Michael Mozina, a fellow we had here before, who claimed the surface of the sun was solid, which doesn't make sense for many reasons.




Fair enough, but I still want to clarify for others that might see that link.



I would tend to say that the Wiki does a better job in attempting to describe some of the features

i.e. spicule

http://en.wikipedia.org/wiki/Spicule_%28solar_physics%29


It certainly does not confuse the issue

Van Rijn
2011-Jun-03, 06:40 AM
i was looking at this stunning picture of the surface of our sun:
http://fettss.arc.nasa.gov/collection/details/sun-sunspots-2/

obviously, the black areas are sunspots but i was wondering about the (in this pic) golden pebble-like structures surrounding them.
what are they made of?


This page has a video illustrating how granules change over time:

http://apod.nasa.gov/apod/ap070522.html

I think it's a lot easier to visualize with a video instead of a static image. As mentioned, this is all hot (mostly hydrogen) gas, rising and falling back, with the slightly cooler bits darker in the image. You can see how the granules are constantly changing, and quite rapidly too. Note the scale in the upper left (showing how wide the Earth would be by comparison), and at the bottom there's a time count (the video runs about ten seconds but it shows the changes happening over about an hour).

PaulLogan
2011-Jun-03, 08:52 AM
great video. thanks!
i've seen similar ones since i started this thread. just fascinating to look at. again and again.

the amount of energy our sun produces is just unimaginable, really. certainly for me it is.
if you then compare the size of the sun to the size of the largest currently known star...
or even with events like grbs!

this universe is a pretty wild place!
who the heck comes up with stuff like that!?

iantresman
2011-Jun-04, 05:13 PM
Everything in that picture is made of the same stuff (mostly hydrogen).

It might be worth mentioning that Solar hydrogen is not like the gas you might find in a balloon, but because the Sun is so hot, the hydrogen is ionized to such as extent that is has dissociated into protons and electrons. There's also about 25% helium, also ionized into helium nuclei (alpha particles!) and an equal number of electrons. This soup of ions is called a plasma, so the Sun consequently consists of 49% electrons, 36% protons, 12% alpha particles, and 2-3% other ions, equivalent to a mixture of 73% hydrogen and 25% helium.

Note: Further to galacsi's comment below (and Swift's), please note that while this is accurate for much of the Sun, it is incorrect for the photosphere where the degree of ionisation is very small (see my post below_

galacsi
2011-Jun-04, 05:53 PM
Hi

I am not sure it is true in the photosphere , deep in the inside of the sun , yes but at the surface , temperature is not high enough. (IMO)

iantresman
2011-Jun-04, 07:21 PM
I stand corrected, and think you may be quite correct, the degree of ionization in the photosphere is only about 10^-4. I've removed my post (subsequently undeleted).

astromark
2011-Jun-04, 07:51 PM
Without wishing to be abrasive or judgemental.
Its obvious that some people do not understand the concept of a star and what it is...
Yes that our sun is a star is missed by some...
So to tell them that its a seething gas ball with fusion at its core and super heated gasses rising and falling in eddies and currents.. Its not like a surface you could point to.. Its a atmosphere. A gas giant.
We at the Ward Observatory have a filter that allows us to directly observe the Solar surface through the 24 cm Cook Refractor.
Fitted with the correct magnification we can directly observe the broiling motions of a living solar surface... Liquid like and seemingly alive. What we are seeing is the upper atmosphere of a star. Its a privileged view. I hope to have helped your understanding.

Swift
2011-Jun-04, 07:51 PM
I stand corrected, and think you may be quite correct, the degree of ionization in the photosphere is only about 10^-4. I've removed my post.
It is excellent that you acknowledge corrections, but please don't delete posts; it comes very close to breaking our revisionism rule (rule 11). It is fine to let it stand and note the correction as you've done. I've restored the post.

iantresman
2011-Jun-04, 08:26 PM
It is excellent that you acknowledge corrections, but please don't delete posts; it comes very close to breaking our revisionism rule (rule 11). It is fine to let it stand and note the correction as you've done. I've restored the post.
My bad.

Tim Thompson
2011-Jun-04, 11:17 PM
If I just do something very simple, (1/2)(mv2) = (3/2)(kT), where v is the rms velocity (http://en.wikipedia.org/wiki/Root_mean_square) and T is the temperature, and let (1/2)(mv2) be the ionization potential for hydrogen (13.598 ev), I get a temperature of 105,000 Kelvins. If the ionization is collisional, then one would expect a very small ionization fraction for hydrogen at solar photospheric temperatures (less than 10,000 Kelvins). I suspect that this is not the case, and the ionization rate is probably dominated by photons. But even so, you still need photons rather more energetic than are found on average in the solar photosphere. Hence, one expects a very low ion fraction in the photosphere, since it is dominated by hydrogen & helium. This makes sense given the ratio of free electron density to neutral hydrogen density found in the photosphere, which ranges from about 0.03 at the base of the photosphere (~9400 Kelvins), to 0.00011 at the minimum temperature in the photosphere (~4600 Kelvins). The free electrons must come mostly from the ionization of the trace heavy nuclei, which have much lower ionization potential, with some from hydrogen atoms ionized by the high energy tail of the photon energy distribution.

So the ionization fraction in the photosphere should be small. But the ionization fraction just below the photosphere, say more than 0.001 of the way from the solar "surface" to the solar core, should become fairly high, since the temperature should quickly exceed 105,000 Kelvins. So the atoms throughout the bulk of the Sun should be mostly, nearly entirely ionized.

Consultation with more detailed sources of information on solar interior models may alter these conclusions, which are really just an approximation. A rigorous solution of the Saha equation (http://en.wikipedia.org/wiki/Saha_ionization_equation) is required to do it all right.