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mugaliens
2008-Nov-05, 04:36 PM
I'm interested in finding out the density of the Sun's surface.

By "surface" I mean the part where, if a spaceship large enough to be seen from earth were to descend, the point at which it disappears from view, covered in "sun-stuff."

What's the density at that altitude?

captain swoop
2008-Nov-05, 04:38 PM
sun stuff?

Argos
2008-Nov-05, 04:48 PM
Don´t have the actual numbers, but I bet it is at least one order of magnitude lower than the Earths atmosphere.

loglo
2008-Nov-05, 04:56 PM
The surface is generally taken to be the photosphere. Its density is "about 0.1% of the density of air at sea level on earth" according to this site (http://www.madsci.org/posts/archives/2001-05/988762969.As.r.html) and 2 x 10^-4 kg/m3 according to this largish PDF (http://astro.berkeley.edu/~fmarchis/Classes/Astro12_summer/presentations/astro12Summer15.ppt) which sounds about right. The Suns average density is 1,400 kg/m3 according to the same source.

loglo
2008-Nov-05, 04:58 PM
Not a bad guess Argos. :)

Argos
2008-Nov-05, 05:02 PM

astromark
2008-Nov-05, 06:02 PM
I'm interested in finding out the density of the Sun's surface.

By "surface" I mean the part where, if a spaceship large enough to be seen from earth were to descend, the point at which it disappears from view, covered in "sun-stuff."

What's the density at that altitude?

Thousands of km deep. Broiling, boiling, extremely hot, in both temperature and radio active emissions... a very hostile place. Your question may not be as simple as you think. Your giant space ship descending into the solar photosphere would be torn apart, vaporised, and burnt, crushed and otherwise. stuffed.:(
If you can imagine screens to shield your descending craft. Then, when would it vanish from view?. In the outer first km. The sun is not dense at that altitude, but norr is it so transparent. At what point do you call a defuse gas ball a surface? This is a subject that is a 'never can do' Why do you ask?...mark.

George
2008-Nov-05, 06:27 PM
Thousands of km deep. I vaguely recall we can see only about 200km or so deep into the photosphere. If the spaceship descends on the outer edge of the disk, then it doesn't have to descend hardly at all due to the CLV (center to limb variation). Only in the central portion of the disk, where we look directly into the interior, can we see several km into it. As a result, in this central region, the effective surface temp. of the Sun is 6390K, and might have a light blue tinge of color to it, but no one knows, not even the Shadow, which avoids the Sun at every turn. :)

mugaliens
2008-Nov-05, 08:13 PM
The surface is generally taken to be the photosphere.

Thanks. But I'm taking it to be the altitude at which that descending spaceship disappears. Does that jibe with your "density is "about 0.1% of the density of air at sea level on earth?"

Would something 1/10th of 1% of Earth's atmosphere (0.0147 psi) hide a spaceship?

mugaliens
2008-Nov-05, 08:20 PM
Thousands of km deep. Broiling, boiling, extremely hot, in both temperature and radio active emissions... a very hostile place. Your question may not be as simple as you think. Your giant space ship descending into the solar photosphere would be torn apart, vaporised, and burnt, crushed and otherwise. stuffed.:(

It's made of unobtanium, with matter/antimatter impulse thrusters capable of 1 Billion Gs, so no worries there.

At the depth it would disappear from an overhead observer, what's the density?

If you can imagine screens to shield your descending craft. Then, when would it vanish from view?. In the outer first km. The sun is not dense at that altitude, but norr is it so transparent. At what point do you call a defuse gas ball a surface? This is a subject that is a 'never can do' Why do you ask?...mark.

Now we're talking. Well, at least making sounds in the right direction. Do you know the density?

George
2008-Nov-05, 09:03 PM
Thanks. But I'm taking it to be the altitude at which that descending spaceship disappears. But that is the photosphere, assuming you are using the visible spectrum. If we could see through the photosphere then "photos" would reveal a smaller disk. ;)

Jeff Root
2008-Nov-06, 07:04 AM
George said 200 km, but my recollection is that the deepest you can see
into the photosphere ranges from about 500 km to 300 km, from the center
of the disk to near the edge. The density varies with depth, but not very
rapidly. A body 500 km under the top of the photosphere would be just
visible if at the center of the disk. It might be able to see bodies 400 km
away from it in the horizontal direction, or 300 km straight below it.

The variation in the depth you can see to, from center to edge, is the
reason the Sun's temperature, color, and brightness vary across the disk.
The Sun is hotter, the deeper you go, so you can only see cooler parts
of the photosphere near the limb.

But George knew that.

-- Jeff, in Minneapolis

astromark
2008-Nov-06, 07:50 AM
And.... I now see this question we can not answer has changed.
He wanted to know how deep into the sun that ship would need to go to not be visible from here. Now its from some place above it. ( safer distance ) So how transparent is the outer layers of the sun ? How quickly does that density increase.
Can I tell him that when you are writing fiction... you can tell lies. As long as they are sort of believable you will be fine. Unobtanium and 1 billion G's... you decide.

" At the depth it would disappear from an overhead observer, what's the density? "

I have no idea. But will add. The solar atmosphere is not transparent. It only looks that way at the top of it because its thin, sparse. descending down into it , you would vanish from view in the top 50 km. Now ask me where the top is... and I will say, were you can see it.

Jeff Root
2008-Nov-06, 08:31 AM
Mark,

The altitude Mugs refers to has a negative value. ...Which isn't to say
that it's worth less than nothing, it just means that it's an altitude below
the top of the photosphere.

At least 200 km (George's memory) or as much as 500 km (mine).
I suggest that you bet on 300 or 400.

-- Jeff, in Minneapolis

hhEb09'1
2008-Nov-06, 09:18 AM
Would something 1/10th of 1% of Earth's atmosphere (0.0147 psi) hide a spaceship?That's just about the density of the Earth's mesosphere. Noctilucent clouds occur there, maybe a spaceship is hiding behind them.

George
2008-Nov-06, 05:25 PM
At least 200 km (George's memory) or as much as 500 km (mine).
I suggest that you bet on 300 or 400.
:) My Google references favor the 300 or 400 values. I have a Livingston book that gives a more accurate value, I would bet. I will look it up tonite. I have a hunch my memory is correct on the 200, but it might have been 200 miles.

astromark
2008-Nov-06, 06:09 PM
Under the heading of completely daft questions... this one is right up there with the best. Ignoring the obvious fact that NOTHING, nothing. Can be said to be able to sink into the suns atmosphere that it would vanish from view..., and then still be able to be said to have survived that. The thought experiment mentality gets tiresome when we try to get so absolutely correct about some thing that can not be done. Its a given that some of the solar outer atmosphere is sparse and density such that an object of some size would remain visible until it descended 100's of km down. More importantly the solar energies would have consumed this object at about the same moment.... I have attempted to be reasonable with this question and looked for information regarding atmospheric pressure and density but, found that temperatures were such that none of it seemed to be relevant. So maybe its 50 or 200 km... whats the point of this please ?

Jeff Root
2008-Nov-06, 06:46 PM
Mark,

Even if there is no alien spaceship hiding in the Sun, we are able to see
down to a certain depth, and that's the answer to mug's question, so it
has a certain charm to it.

Besides, you need to know these things when your'e the King.

-- Jeff, in Minneapolis

mugaliens
2008-Nov-06, 09:37 PM
Ignoring the obvious fact that NOTHING, nothing. Can be said to be able to sink into the suns atmosphere that it would vanish from view..., and then still be able to be said to have survived that. The thought experiment mentality gets tiresome when we try to get so absolutely correct about some thing that can not be done.

And this stops us from exploring the physics near an event horizon?

Please indulge me. So far we've got about 300-400 km depth at which our fictitious impenetraship is fully concealed from overhead view.

Since the depth estimates range in the 100s of km, let's determine the density at, say, 10 km, 50 km, 100 km, 500 km, and so on, and we can worry about the precise depth a bit later.

I have attempted to be reasonable with this question and looked for information regarding atmospheric pressure and density but, found that temperatures were such that none of it seemed to be relevant. So maybe its 50 or 200 km... whats the point of this please ?

Imagine if the Wright brothers had gone to their local horseless carriage maker and asked him to build them an engine. After discussing the particulars, particularly about making it as light as possible, the manufacturer stood his ground, knowing that what these boys really needed was something sturdy, something that would last!

The Wrights were faced with just such an issue, as several engine manufacturers "met their need for a sufficiently light powerplant." It was their shop mechanic, Charlie Taylor, who built an engine with enough HP/weight ratio to enable the Wright Flyer to get off the ground.

The point is to explore new frontiers! Diving to the depths of the Mariana Trench was, at one time, thought to be impossible. But it never would have occured if the thought of it's impossibility eclipsed the idea of it's possibility, the idea of which lead to a series of designs capable of ever-deeper dives.

Let's get back to our star, the Sun, and see where we're at with respect to the deapth and density at which point an impenetratium spacecraft would disappear from overhead view.

ngc3314
2008-Nov-06, 10:15 PM
More or less by definition, the photosphere marks the level from which 1/e of the radiation emerges to large distances - pick a slightly deeper level for more complete invisibility (since our spacecraft protected by magic pixie dust will probably be black against the surroundings). I have a copy of Zombeck's Handbok of Space Astronomy here on my desk - slghtly dated but few values have changed much. Two graphs of density versus height from the (vertical-view, I gather) photosphere give number density of particles at 6x10^6 and 3x10^6 /cm^3 (that last is for electron density so a factor of 2 makes sense). For ionized hydrogen, multiply 3x10^6 by the atomic mass and that gives 5x10^(-16) g/cm^3. If a red giant is a red-hot vacuum, the photosphere is a white-hot vacuum (Hi, George!). Otherwise expressed, I make that (dividing by 1.5e-12,also from Zombeck) about 0.0003 times sea-level density on Earth (if I got all those numbers punched right). Long column lengths make up for a lot.

Zombeck's book has a lot of very useful information crammed in - the second edition been scanned here ( http://ads.harvard.edu/books/hsaa/).

George
2008-Nov-06, 10:23 PM
More importantly the solar energies would have consumed this object at about the same moment.... Not necessarily. I missed the other threads on this (recalling the Sunshine movie not long ago), but was it decided that nothing could stay in one piece in travleing 300 km or so through the photosphere? Temperature alone won't destroy it; time is required, too. Consider the surface temperatures of large meteors. They can often survive our atmosphere all too well.

Jeff Root
2008-Nov-07, 03:55 AM
In a thread here over a year ago, I asked how large an asteroid would need
to be to survive a plunge into the Sun. By that I just meant that some of
it would end up as matter in the Sun rather than vapor blown away from
the Sun by solar wind. I don't recall getting an answer.

-- Jeff, in Minneapolis

peter eldergill
2008-Nov-07, 04:12 AM
Obviously the density of the surface of the sun is identical to that of Iron as clearly the sun's surface is made of iron ...

<runs and hides>

Pete

Ken G
2008-Nov-07, 04:35 AM
In a thread here over a year ago, I asked how large an asteroid would need
to be to survive a plunge into the Sun. By that I just meant that some of
it would end up as matter in the Sun rather than vapor blown away from
the Sun by solar wind. I don't recall getting an answer.
I can't say exactly how large it would need to be, but I shouldn't think large at all. I imagine a rock the size of your hand would survive such a plunge, with ease. I'd bet even a pebble would, but I can't say for sure. Now, a dirty snowball of ice and loosely bound grains of dust, that's another matter-- grains of dust smaller than about a micron get blown off by the solar radiation. The solar wind has almost no effect on anything except individual charged atoms and molecules.

George
2008-Nov-07, 05:20 AM
... my recollection is that the deepest you can see
into the photosphere ranges from about 500 km to 300 km, from the center.
I like your memory better than mine. According to Livingston & Bhatnagar's Fundamentals of Solar Astronomy (pg. 117), the optical depth is about 400 to 500km.

...the photosphere is a white-hot vacuum (Hi, George!). :) I haven't caught you with an off-color remark yet!

I can't say exactly how large it would need to be, but I shouldn't think large at all. I imagine a rock the size of your hand would survive such a plunge, with ease. Yes, and I think the Roche limit isn't a factor for rigid bodies falling into the Sun, either.

I still like the conjecture of three planet-sized objects being gobbled-up by their host star, V838 Mon, to explain the three very bright flashes observed.

astromark
2008-Nov-07, 09:57 AM
Oops... when I mentioned the size of the object being dumped or descending into Sol. It was not because size has anything to do with this other than the ability to see a larger object from some distant place. Size does., it has been said. Mater. Those smaller particle's do just get blown away by the solar energy. Unfortunately the plasma state of mater and the super hot temperatures of the Sun's surface would seem to prohibit any object ever reaching deep into the sun. As for the inbound meteor... carbon vapor.

Eroica
2008-Nov-07, 11:55 AM
George said 200 km, but my recollection is that the deepest you can see
into the photosphere ranges from about 500 km to 300 km...
That's pretty much what I heard, but several decades ago the estimate was as high as 1000 km.

mugaliens
2008-Nov-07, 06:43 PM
More or less by definition, the photosphere marks the level from which 1/e of the radiation emerges to large distances - pick a slightly deeper level for more complete invisibility (since our spacecraft protected by magic pixie dust will probably be black against the surroundings). I have a copy of Zombeck's Handbok of Space Astronomy here on my desk - slghtly dated but few values have changed much. Two graphs of density versus height from the (vertical-view, I gather) photosphere give number density of particles at 6x10^6 and 3x10^6 /cm^3 (that last is for electron density so a factor of 2 makes sense). For ionized hydrogen, multiply 3x10^6 by the atomic mass and that gives 5x10^(-16) g/cm^3. If a red giant is a red-hot vacuum, the photosphere is a white-hot vacuum (Hi, George!). Otherwise expressed, I make that (dividing by 1.5e-12,also from Zombeck) about 0.0003 times sea-level density on Earth (if I got all those numbers punched right). Long column lengths make up for a lot.

Zombeck's book has a lot of very useful information crammed in - the second edition been scanned here (http://ads.harvard.edu/books/hsaa/).

Thanks! Wikipedia says the density at the lower photosphere is 2x10-4 kg/m

So, it's hotter than rocket exhaust, but pretty darn thin. By comparison, Earth's atmosphere is 1.2 kg/m[sup3. And this graph (http://en.wikipedia.org/wiki/Image:Atmosphere_model.png)clearly indicates that the comparable altitude on Earth of the sun's lower photosphere is... (come on, folks, exercise those unit conversion muscles...)

George
2008-Nov-07, 06:47 PM
That's pretty much what I heard, but several decades ago the estimate was as high as 1000 km.
Uh oh. :)

sabianq
2008-Nov-07, 07:44 PM

http://www.thesurfaceofthesun.com/

The sun's photosphere is often mistakenly referred to as the surface of the sun. In reality however, the sun's photosphere is only a "liquid-like" plasma layer made of neon that covers the actual surface of the sun.

is the actual surface of the sun Iron as Peter suggests in an earlier post?

http://arxiv.org/ftp/astro-ph/papers/0511/0511379.pdf

Helio-seismology data have since confirmed stratification at a relatively shallow depth beneath the visible photosphere, at ≈ 0.5% solar radii (≈0.005 Ro)

figure 2 page 4

A "running difference" image of the rigid, iron-rich structures beneath the photosphere in a small part of the Sun's surface revealed by the TRACE satellite using a 171 Å filter [10]. This filter is specifically sensitive to light emitted from Fe (IX) and Fe (X) iron ions.

The team that operates the TRACE satellite system for NASA made a movie of the flare and mass ejection event that occurred from this Active Region 9143 on 28 August 2000. You can see the movie at http://trace.lmsal.com/POD/movies/T171_000828.avi or it is available here: http://vestige.lmsal.com/TRACE/Public/Gallery/Images/movies/T171_000828.avi.

and here:

http://www.sciencedaily.com/releases/2002/07/020717080229.htm

Dr. Oliver Manuel, a professor of nuclear chemistry at UMR, says iron, not hydrogen, is the sun's most abundant element.

sabianq
2008-Nov-07, 08:00 PM
and here:
http://www.astro.umd.edu/~white/papers/03_norh_020723.pdf

The 195 °A passband of TRACE is dominated by an Fe XII line formed at 1–2 106 K,
but also contains an Fe XXIV line at 192.03 °A (formed at 10-20 106 K) that is usually much
weaker (Handy et al. 1999). Images at different wavelengths are coaligned to within about 5 using
common features.

http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/pdf/2008/13/aa9034-07.pdf

A specific type of AR emission known as “moss” was clearly
visible in 171 Å images (dominated by Fe ix and Fe x emission)
taken by the Transition Region And Coronal Explorer (TRACE;
Berger et al. 1999; de Pontieu et al. 1999).

Fe xii line ratios are sensitive to the density range from 107 to
1012 cm−3, which provides an opportunity to measure densities
in the core, as well as in the outer regions of ARs. As is evident
from the density map, the density is highest in the core of
the AR [active region] and reaches values up to 1010.5 cm−3. We also derived
the density maps using line ratios from Mg vii (λ280/λ278),
Fe xiii (λ203/λ202), and Fe xiv (λ264/λ274) and found that the
densities in the core of the ARs were highest at all these temperatures
(Tripathi et al. 2007).

peter eldergill
2008-Nov-07, 08:34 PM
Heh...I was joking about the iron sun. Do a quick search and you'll see that folks here have discussed it ad nauseum (sorry about any mixups, I assumed people could tell I was joking)

Pete

mugaliens
2008-Nov-07, 08:45 PM
But if it is iron...

Nevemind.

:)

sabianq
2008-Nov-07, 08:53 PM
Heh...I was joking about the iron sun. Do a quick search and you'll see that folks here have discussed it ad nauseum (sorry about any mixups, I assumed people could tell I was joking)

Pete

i did do a search and found that the discussions were closed and were done before the most recent TRACE findings which actually suggest that the surface of the sun is below the photosphere and does indeed show spectral lines indicating a very heavy presence of iron.

I would think that new information could warrant a second look.

it is possible that the data is incorrect and in error.

http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.2484v1.pdf
september 2008

and this article Submitted to the Hirschegg Workshop ’06: Astrophysics and Nuclear Structure
Hirschegg/Austria, 15-21 January 2006

http://arxiv.org/ftp/astro-ph/papers/0511/0511379.pdf

The finding of an unexpectedly large source of energy from repulsive interactions between neutrons in the 2,850 known nuclides has challenged the assumption that H-fusion is the main source of energy that powers the Sun and other stars.

We will show below that repulsive interactions between neutrons in such condensed nuclear matter is the driving force that generates an outpouring of hydrogen and luminosity from a chemically stratified, iron-rich Sun [3-11] and a likely energy source elsewhere in the cosmos.

shows some very interesting stuff

Ken G
2008-Nov-07, 10:13 PM
The quotes above are vastly inaccurate-- if that is what the paper has to offer, don't waste your time. For example, the quote asserts that it is an "assumption" that hydrogen fusion is the source of solar energy, but the fact is, the structure of the interior of the Sun is well constrained by observations, and does indeed reach hydrogen fusion temperatures, in a quantitatively correct way to be interpreted as just that. Furthermore, the neutrinos associated with hydrogen fusion have been measured at Earth, and indeed were the source of the discovery of "neutrino oscillations", now a standard aspect of neutrino physics. Also, the article was "submitted" in 2006, but no refereed articles by these authors appear anywhere. Instead, we find a flurry of conference activity in 2005, and nothing else. I'm afraid it's pretty obvious we are dealing with the phenomenon known in official academic parlance as "flakes", but more respectfully labeled here as "ATM".

Tinaa
2008-Nov-07, 10:39 PM
sabainq do not post anymore ATM stuff in Q & A.

peter eldergill
2008-Nov-08, 01:12 AM
sabainq do not post anymore ATM stuff in Q & A.

Sorry..it was me who started it :o

Pete

sabianq
2008-Nov-08, 01:32 AM
<sigh>

Van Rijn
2008-Nov-08, 02:14 AM
i did do a search and found that the discussions were closed and were done before the most recent TRACE findings

There were repeated discussions (and attempts to rectify misunderstandings of Iron Sun advocates) of TRACE images. Search on "TRACE EUV" and "TRACE 171A" for a number of them. This stuff was covered over and over and over and over . . .

<sigh>

Yes, that's pretty much how I feel about the subject.

sabianq
2008-Nov-08, 02:30 AM
yea, im sorry bout that,
i just read the papers and got all excited.
thought it was new info.

mugaliens
2008-Nov-09, 11:27 AM
yea, im sorry bout that,
i just read the papers and got all excited.
thought it was new info.

It may help to use BAUT's rather good search engine, located in your friendly neighborhood upper-right-hand corner, to ensure any "new info" hasn't been hashed to death here, before. Often, you may find that it was discussed, but without resolution, at which point the info you have may represent a new approach. Nothing wrong with resurrecting an old thread, as doing so is, for the rest of us, often like finding the missing one of a pair of favorite old slippers under the bed.

Gigabyte
2008-Nov-09, 03:48 PM
The search engine is often worse than useless when looking for topics.

mugaliens
2008-Nov-09, 10:48 PM
The search engine is often worse than useless when looking for topics.

And often, it's not. Either way, it's worth a try.

Van Rijn
2008-Nov-09, 11:11 PM
The search engine is often worse than useless when looking for topics.

The google search works very well, though. Look at the upper right corner of the screen, or you can go to google and enter the URL yourself.

Van Rijn
2008-Nov-09, 11:25 PM
Often, you may find that it was discussed, but without resolution, at which point the info you have may represent a new approach.

I suppose it depends on what you mean by "resolution" but usually, the resolution to an ATM idea comes rather quickly, when major misunderstandings or misinterpretations are pointed out. A resolution, of course, doesn't stop the ATM proponent from continuing to argue their misunderstandings.