

Time lapse of the Sun reveals the largest sunspot in 24 years - wglb
http://www.vox.com/xpress/2014/11/10/7186251/time-lapse-sun-sunspot-ar2192-solar-flares

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gcb0
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?

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FoeNyx
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...](http://sdo.gsfc.nasa.gov/assets/img/latest/latest_1024_0193pfss.jpg)

~~~
mturmon
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](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](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.

~~~
FoeNyx
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...](http://sdo.gsfc.nasa.gov/assets/img/latest/f_094_335_193_1024.jpg)
, 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.

~~~
mturmon
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_...](http://sdo.gsfc.nasa.gov/assets/img/latest/mpeg/latest_1024_0131_venus.mp4)

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

~~~
andrewstuart2
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.

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lutorm
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... ;-)

~~~
demallien
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_.

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FoeNyx
"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'."

~~~
mturmon
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.

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

~~~
micampe
The YouTube description says it's 304 ångström ultraviolet.

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FoeNyx
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)

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deadfall
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.

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

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MaysonL
Yes, for details see:
[https://en.wikipedia.org/wiki/Solar_rotation](https://en.wikipedia.org/wiki/Solar_rotation)

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FoeNyx
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)

