APOD: Across the Sun (2015 Apr 30)

Comments and questions about the APOD on the main view screen.
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APOD: Across the Sun (2015 Apr 30)

Postby APOD Robot » Thu Apr 30, 2015 4:06 am

Image Across the Sun

Explanation: A long solar filament stretches across the relatively calm surface of the Sun in this telescopic snap shot from April 27. The negative or inverted narrowband image was made in the light of ionized hydrogen atoms. Seen at the upper left, the magnificent curtain of magnetized plasma towers above surface and actually reaches beyond the Sun's edge. How long is the solar filament? About as long as the distance from Earth to Moon, illustrated by the scale insert at the left. Tracking toward the right across the solar disk a day later the long filament erupted, lifting away from the Sun's surface. Monitored by Sun staring satellites, a coronal mass ejection was also blasted from the site but is expected to swing wide of our fair planet.

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Re: APOD: Across the Sun (2015 Apr 30)

Postby Ron-Astro Pharmacist » Thu Apr 30, 2015 3:50 pm

After the teaser yesterday I was expecting something like this.

Click to play embedded YouTube video.


If so, then I suppose it would have been "Elevator to the Moon". :wink:
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Ron-Astro Pharmacist » Thu Apr 30, 2015 5:25 pm

I think the Black Sun and Inverted Starfield from the "negative or inverted" link is amazing.

If Arthur Eddington http://en.wikipedia.org/wiki/Arthur_Eddington had this technology would it have been feasible to show the distortion of spacetime caused by the sun's gravity? Or would that be distortion be visible in a narrowband image as in the link?

If a similar magnified image could be made at the moment the sun eclipsed a planet and the image could be manipulated in a way to incorporate the planet as visible, I'm curious if it would make an interesting APOD someday?
I don't know how often planets physically pass behind the sun, from vantage point of the Earth, rather than just in its glare. Something like this?

http://www.nakedeyeplanets.com/movements.htm

Love the "Dance of the Planets!" :D
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Thu Apr 30, 2015 6:02 pm

Ron-Astro Pharmacist wrote: If Arthur Eddington http://en.wikipedia.org/wiki/Arthur_Eddington had this technology would it have been feasible to show the distortion of spacetime caused by the sun's gravity?

No. The distortion is far too small to be visible in an image.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby AndrewMGarland » Thu Apr 30, 2015 6:06 pm

Why does the Sun appear as a definite disk? Made of hot gas, it could appear as a fuzzy ball with slowly increasing density. Why does it appear to have a surface?

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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Thu Apr 30, 2015 6:24 pm

AndrewMGarland wrote:Why does the Sun appear as a definite disk? Made of hot gas, it could appear as a fuzzy ball with slowly increasing density. Why does it appear to have a surface?

It does have a fuzzy edge. But the depth of that fuzziness is very small compared with the radius of the Sun. The Sun consists of matter in a fluid state (except possibly the core). Its outer "boundary" is determined by the balance between gravity and radiation pressure. This results in a steep density gradient across the photosphere (the approximately 2000 km thick, fairly transparent zone above the photosphere)- about 10 orders of magnitude. As a result, the photosphere marks the boundary where the Solar material is effectively opaque, and that's why we see it as a surface.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Boomer12k » Thu Apr 30, 2015 6:53 pm

Awesome strand... I like the ARCH filament to the left with the 3 arches..looks like a GRAZING SUN ANIMAL... :D

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Re: APOD: Across the Sun (2015 Apr 30)

Postby geckzilla » Thu Apr 30, 2015 8:21 pm

Chris Peterson wrote:
Ron-Astro Pharmacist wrote: If Arthur Eddington http://en.wikipedia.org/wiki/Arthur_Eddington had this technology would it have been feasible to show the distortion of spacetime caused by the sun's gravity?

No. The distortion is far too small to be visible in an image.

Somewhat related; I was surprised to discover that we have instruments sensitive enough to detect the wandering of distant radio sources due to the Sun's distortion as Earth orbits it.
Paper: http://arxiv.org/abs/1502.07395
It was pointed out to me in a blog post by Sabine Hossenfelder.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Phudman » Thu Apr 30, 2015 10:06 pm

What is "the light of ionized hydrogen atoms.."? Is this light from recombination to the single proton (that is ionized hydrogen)? Or perhaps light from ionized Helium?

Wonderful picture.

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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Thu Apr 30, 2015 10:45 pm

Phudman wrote:What is "the light of ionized hydrogen atoms.."? Is this light from recombination to the single proton (that is ionized hydrogen)? Or perhaps light from ionized Helium?

This is the light of H-alpha (Balmer series, n=3 to n=2, 656 nm).
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Dad is watching » Fri May 01, 2015 2:57 am

Chris Peterson wrote:The Sun consists of matter in a fluid state (except possibly the core).


A fluid state or a plasma state? I didn't think they were the same...

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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Fri May 01, 2015 4:11 am

Dad is watching wrote:
Chris Peterson wrote:The Sun consists of matter in a fluid state (except possibly the core).

A fluid state or a plasma state? I didn't think they were the same...

A fluid can be gas, plasma, or liquid. Even a solid in certain cases.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby geckzilla » Fri May 01, 2015 4:40 am

Chris Peterson wrote:A fluid can be gas, plasma, or liquid. Even a solid in certain cases.

Alright, mister. I'm interested. Toss me a link or something, will you? There is a mention on Wikipedia of plastic solids but it just leads to the plastics article, which doesn't get into the topic as far as I can tell.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Fri May 01, 2015 5:01 am

geckzilla wrote:
Chris Peterson wrote:A fluid can be gas, plasma, or liquid. Even a solid in certain cases.

Alright, mister. I'm interested. Toss me a link or something, will you? There is a mention on Wikipedia of plastic solids but it just leads to the plastics article, which doesn't get into the topic as far as I can tell.

The mantle of the Earth is a good example of a plastic solid. It is a solid by most definitions, yet under high pressure it flows. The rock seen below (at the Black Canyon of the Gunnison) shows evidence of plastic deformation, as well. It flowed under very high pressure. Had it been hot enough to melt, the mineralogy would be very different.

DSCN7660p.jpg
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Ann » Fri May 01, 2015 7:52 am

Chris Peterson wrote:
AndrewMGarland wrote:Why does the Sun appear as a definite disk? Made of hot gas, it could appear as a fuzzy ball with slowly increasing density. Why does it appear to have a surface?

It does have a fuzzy edge. But the depth of that fuzziness is very small compared with the radius of the Sun. The Sun consists of matter in a fluid state (except possibly the core).



So what about the core? If it is not in a fluid state, then what state is it in?

Chris Peterson wrote: Its outer "boundary" is determined by the balance between gravity and radiation pressure. This results in a steep density gradient across the photosphere (the approximately 2000 km thick, fairly transparent zone above the photosphere)- about 10 orders of magnitude. As a result, the photosphere marks the boundary where the Solar material is effectively opaque, and that's why we see it as a surface.


Is there a mistake here? You talk about the photosphere twice, when you might possibly mean two different "layers" of the Sun.

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Re: APOD: Across the Sun (2015 Apr 30)

Postby neufer » Fri May 01, 2015 1:38 pm

Click to play embedded YouTube video.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Fri May 01, 2015 1:41 pm

Ann wrote:So what about the core? If it is not in a fluid state, then what state is it in?

It's almost certainly fluid. But I think there is some uncertainty about the behavior of material at the pressures involved.

Ann wrote:
Chris Peterson wrote: Its outer "boundary" is determined by the balance between gravity and radiation pressure. This results in a steep density gradient across the photosphere (the approximately 2000 km thick, fairly transparent zone above the photosphere)- about 10 orders of magnitude. As a result, the photosphere marks the boundary where the Solar material is effectively opaque, and that's why we see it as a surface.

Is there a mistake here? You talk about the photosphere twice, when you might possibly mean two different "layers" of the Sun.

Sorry. Meant chromosphere, the layer above the photosphere.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby MarkBour » Fri May 01, 2015 9:37 pm

This is one beautiful APOD.

I was struck by the video that neufer posted. It appears that the coronal mass ejection was accompanied by an opposite ejection as well. Is this common? I wonder about the mechanism of an ejection, and why it would occur on opposite sides of the Sun. What very little I know about it, the gas is all flowing under the influence of massive magnetic force. Something must cause a "line of force" to "spread out" (I'm using quotes here because I'm well beyond my knowledge at this point), carrying a huge amount of mass away from the surface (the photosphere boundary). Either the magnetic force settles and stops expanding, or, in the case of a CME, it disconnects and flies on out, taking some of the gas with it. (I read the "Cause" section on the Wikipedia article on CME, which is pretty cursory.) I can imagine that when one huge magnetic loop is moving outward, that on the opposite side of the Sun, another line is likely to do the same. If anyone has further explanation to help me, I'd appreciate your sharing, it's fascinating.

Chris noted that the photosphere is the point at which the material appears opaque. True enough in this image. But, I wonder if the edge of the photosphere is actually the point at which the material becomes opaque in the usual sense, or if he is using "opaque" in a special sense here. Normally, opaque would mean that light does not pass through something. If the gas is mainly hydrogen, is there a given density at which hydrogen gas becomes opaque, and is that what causes the photosphere? It seems possible to me that light can pass through the material just fine, but since the material is a dazzling light source, we will never see light passing through the photosphere.

When the CMEs and flares occur, no doubt the sun (a) wobbles, and (b) undergoes significant changes in light output. I wonder if Kepler has ever seen such events and mistaken them for planet transits ... I seem to recall that the Kepler project looks for regularly repeated occurrences of these events, so since these flares and CMEs are evidently random in appearance, they would easily be factored out, if given a little time.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby DavidLeodis » Fri May 01, 2015 9:38 pm

I would be grateful if someone could help with something I am unsure about. The subject of the image is the solar filament, which I assume is the flame like feature to the upper left. I understand however that filaments normally appear dark against the Sun but here it seems lighter. I wonder therefore if that is because the image is a "negative or inverted narrowband image" :?:

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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Fri May 01, 2015 10:47 pm

DavidLeodis wrote:I would be grateful if someone could help with something I am unsure about. The subject of the image is the solar filament, which I assume is the flame like feature to the upper left. I understand however that filaments normally appear dark against the Sun but here it seems lighter. I wonder therefore if that is because the image is a "negative or inverted narrowband image" :?:

Yes. The image has been inverted. I have no idea why, since it adds nothing in terms of bringing out detail, and creates some confusion. Here's what it should look like. An altogether better representation, IMO.

GS_20150427_Sun_1000_inv.jpg
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Re: APOD: Across the Sun (2015 Apr 30)

Postby Chris Peterson » Fri May 01, 2015 10:58 pm

MarkBour wrote:It appears that the coronal mass ejection was accompanied by an opposite ejection as well. Is this common? I wonder about the mechanism of an ejection, and why it would occur on opposite sides of the Sun.

There is no mirroring effect like this. What happens on one side is unrelated to what happens on the other.

Chris noted that the photosphere is the point at which the material appears opaque. True enough in this image. But, I wonder if the edge of the photosphere is actually the point at which the material becomes opaque in the usual sense, or if he is using "opaque" in a special sense here.

I mean opaque in its usual sense. The ratio of transmitted light to absorbed light is very low below the surface of the photosphere. A photon cannot travel far in the plasma without being absorbed. Density is one factor, but the behavior of photons in plasmas is another.

When the CMEs and flares occur, no doubt the sun (a) wobbles, and (b) undergoes significant changes in light output. I wonder if Kepler has ever seen such events and mistaken them for planet transits ... I seem to recall that the Kepler project looks for regularly repeated occurrences of these events, so since these flares and CMEs are evidently random in appearance, they would easily be factored out, if given a little time.

Correct. Planetary occultations show regularity, and that is part of the Kepler data analysis. A bigger problem is starspots, which can last long enough in some cases to come around more than once. These can quite closely mimic the photometric appearance of planets.
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Re: APOD: Across the Sun (2015 Apr 30)

Postby DavidLeodis » Sat May 02, 2015 11:45 am

Thanks Chris for your help regarding my confusion about the filament. :)


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