Time lapse of the Sun reveals the largest sunspot in 24 years | Hacker News Reader

Time lapse of the Sun reveals the largest sunspot in 24 years

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69 pointswglb26 comments

why the flares slide back to were they came from as if the video was rewinding instead of falling down back as one would expect from gravity?

Plasma moves along magnetic field lines. Which is a really important part of how plasma containment works in a tokamak nuclear fusion reactor's. Also, these features are mind bogglingly big and gravity is only 28g's on the surface of the sun. http://www.thesuntoday.org/solar-facts/how-big-is-the-sun/

I'm far from being an expert, but my understanding is that magnetic forces are really intense around solar spots, and that a change of polarity might channel back some ejected coronal matter.

See the current magnetic field lines : http://sdo.gsfc.nasa.gov/assets/img/latest/latest_1024_0193p...

You are quite right. The charged particles in the flare are following magnetic field lines, which run (typically) from one point on the Sun's surface, up through its atmosphere, and then back down to another point. The diagram you linked illustrates this very well.

There is one other wrinkle, which is that the video shows only a relatively narrow frequency range of light. The full list is at http://aia.lmsal.com/public/instrument.htm ; the video was made from just one frequency band from that list.

Each band is sensitive to plasma within one particular temperature range. So, as plasma heats or cools, it can disappear from the image even though it is still there.

By combining the information from the various temperature ranges (i.e., various frequency ranges) you can reconstruct heating/cooling of packets of plasma as they travel through the solar atmosphere. The ranges were chosen to sample about equally in log(temperature) -- rightmost column of the list above.

The reason this is so important is that the temperature of the atmosphere increases dramatically as you go up, and we don't understand why. This is the "coronal heating problem" (http://en.wikipedia.org/wiki/Corona#Coronal_heating_problem).

If you look at the video, you could get the impression that the pictures are just giving a visual impression of where flaring is happening. In fact, because of the sampling process described above, they are used in a quantitative way to initialize 3D magneto-hydrodynamic models so that the flows can be modeled and predicted. It's embryonic weather forecasting, but for a different atmosphere.

Very Interesting, thank you!

But it seems there are several methods to create composite views on SDO website (several freq ranges used as RGB of the output composite images). I guess there isn't one easy way to visualize all of this, or is it ? Do you know if the embryonic "3D magneto-hydrodynamic models" are by any chance available on the web to play with ? :)

Also, in the case of the video, I don't know the intent of the creator so it's just a supposition, but if it's for science vulgarisation rather than science exactitude, I guess a composite view, as http://sdo.gsfc.nasa.gov/assets/img/latest/f_094_335_193_102... , would have be less appealing to the targeted public, as it would look way more artificial than the red/orange sun shown in the video (though it is also a totally arbitrary colouring). The suspension of disbelief in "hey look it's our Sun!" is probably easier using those culturally accepted warm colour tones to represent it.

I don't know of one particular way to visualize all the bands. Sometimes at conferences you will see specialists' posters with composite views like the one you linked. But usually they will show the individual bands separately, side by side.

I think the colorings were chosen by the predecessor instrument to SDO/AIA, which was on SoHO, and they have just been retained. It's funny, I never thought to ask who came up with them, because AFAIK they are arbitrary.

You need an expert to drive the MHD models. They are still in development, although you can find videos online.

Incidentally, I notice there is a nice video showing the transit of Venus:

http://sdo.gsfc.nasa.gov/assets/img/latest/mpeg/latest_1024_...

I’m not a physicist, but the motion of flares is governed more by eletromagnetic forces than gravity. Each flare loop tracks the Sun’s magnetic field (I believe).

I saw that too, and it drove me crazy.

My theory is that either it's an artifact of the lens system on the camera, or more likely, what we're actually seeing is not the flair, but a reflection of the flair on the ball of the sun.

Think what it would look like if you had a shiny ball (a Christmas tree ornament), and there were flairs coming off of that. As the flair went out from the ball and fell back, you would see it's reflection in the surface of the ball, and I think it would look a lot like those flairs look.

Incredible. But, one word: "screensaver". (Especially, if anyone can do it, Chromecast screensaver!?)

My quick and dirty solution. Worked at least for my (Linux) laptop.

1. Chrome > Dev tools > Network tab > Search "webm" (everybody uses html5 video, right?) > Right click a request, "copy as CURL".

2. Insert into CLI, remove &range=- parameter, and redirect output to some file (or use -o curl option)

3. mplayer somefile.webm -rootwin -vf scale=1920:1080 (or whatever)

I'm sure there's a better/easier way, but it's a start.

That sunspot was easily visible to the naked (but properly protected) eye. It was quite remarkable. Alternatively, you could see it by projecting an image of the sun on a paper with a lens. (Works best with long focal length lenses so you don't set the paper on fire... ;-)

Yup, I got a good look at it on my way to work in Paris. It was one of those days where there is enough cloud that you can look at the sun without it hurting, but the sun is still visible through the clouds. I've been looking for sunspots on these occasions for about 10 years now, but thanks to a particularly quiet sun over that period, I haven't had any luck. So imagine my delight to look up and see the sunspot pretty much instantly. I mean this sucker was big.

"AR 2192 has now rotated onto the other side of the Sun as of early November, and it's unclear if it will still be around when that part of the star rotates back to face us again."

Well apparently AR 2192 might be ending its farside trip as soon as tomorrow or the day after (if it still exists of course).

Also something noteworthy from the youtube video description : "The animation has been rotated 180 degrees so that south is 'up'."

About the rotated animation: The image source is the SDO satellite, which happens to be standing on its head while orbiting the Earth. So, its raw images already came in rotated by 180 degrees. (Well, within 1 degree of 180 anyway -- determining the precise angle is rather difficult[+].)

I get the feeling that the person who made the video did not know this, and just made the video by linking the still science images, which are freely available.

To anyone who is used to solar imagery, seeing the Sun rotating backward is very disconcerting. To a real specialist, seeing that particular AR upside down is also disorienting.

[+] You can't find the Sun's equator or poles very accurately, so I think the instrument team used the transit of Venus (possibly Mercury) between the camera and the Sun to establish the angle calibration.

We have STEREO [1] for a glimpse on the far side of the sun.

[1] http://www.nasa.gov/mission_pages/stereo/main/

Does anyone know if these are visible light pictures? Or are they false colored images of a different part of the spectrum?

The YouTube description says it's 304 ångström ultraviolet.

Found this description, on ESA website, for an old SOHO picture taken around 304 Å : "304 Å : spectral line emitted by ionised helium (He II). Corresponding to a temperature of about 60,000 Kelvin, emission in this line shows the upper chromosphere of the Sun."

That gives another meaning to the expression "hot like HeII" ... sorry ;)

(but apparently it's less hot that the pictures in 94 Å linked to emission of Fe XVIII with temperature of about 7,000,000K)

Aren't sunspots darker than the rest of the sun in visible light? Must be because the output has all shifted to UV.

> visible light pictures

I don't think it's even physically possible to capture the sun that close in the normal light spectrum.

Everytime I see pictures or video of the Sun I feel very small. Some of the solar flares are bigger than our planet. I am not even going to mention the Hubble Ultra-Deep Field poster on my wall that has around 10,000 galaxies.

This makes it look like the sun is rotating. Is that true?

The visual effect of rotation in the video is a combination of the rotation of the sun and the orbit of the Earth around the sun (the satellite that took the images used to create the video is in orbit around the Earth[1]). Ballpark combining the rotation of the sun and the orbit of the Earth gives a rotation period of about 26-27 days[2], so during the video (made from 16 days of images), the Sun would appear to rotate about 16/26.5 * 360 = 217 degrees.

1. https://en.wikipedia.org/wiki/Solar_Dynamics_Observatory#Orb...

2. https://en.wikipedia.org/wiki/Solar_rotation#Sidereal_rotati...

Yes, for details see: https://en.wikipedia.org/wiki/Solar_rotation

Interesting excerpts from the details : * "On the surface the Sun rotates slowly at the poles and quickly at the equator." (~26d vs 38d) * "The rotation rate through the interior is roughly equal to the rotation rate at mid-latitudes, i.e. in-between the rate at the slow poles and the fast equator." (interior being <0.7 radius)

The sun rotates on its equator once every 25 days.

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