Starship Asterisk*

AR 2192: Giant on the Sun

Explanation: As you (safely!) watched the progress of yesterday's partial solar eclipse, you probably also spotted a giant sunspot group. Captured in this sharp telescopic image from October 22nd the complex AR 2192 is beautiful to see, a sprawling solar active region comparable in size to the diameter of Jupiter. Like other smaller sunspot groups, AR 2192 is now crossing the Earth-facing side of the Sun and appears dark in visible light because it is cooler than the surrounding surface. Still, the energy stored in the region's twisted magnetic fields is enormous and has already generated powerful explosions, including two X-class solar flares this week. Coronal mass ejections (CMEs) associated with the flares have not affected planet Earth, so far. The forecast for further activity from AR 2192 is still significant though, as it swings across the center of the solar disk and Earth-directed CMEs become possible.

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It's Halloween on the Sun.

Ann

I see Van Gogh's sunflowers.

Govett wrote:I see Van Gogh's sunflowers.

I do, too!

If the sunspots are dark because they are cooler than the rest of the sun does it mean if we take a photo encompassing only the region of a sunspot we'd see it more bright?

What I mean is, do we see sunspots as dark because the photo in question adjusted for the brightness of the overall regions of the sun?

Ludo wrote:If the sunspots are dark because they are cooler than the rest of the sun does it mean if we take a photo encompassing only the region of a sunspot we'd see it more bright?

What I mean is, do we see sunspots as dark because the photo in question adjusted for the brightness of the overall regions of the sun?

Almost every image is adjusted so that the darkest part is black and the lightest is white. Or exposed that way via the zone system. And our eyes and brains do this when we look at things, as well- we see black and white by moonlight and by sunlight, even though the absolute intensity difference is many orders of magnitude (consider that the Moon itself is the color of a lump of coal...)

Sunspots are blazingly bright. If the entire surface of the Sun were the temperature (and brightness) of a sunspot, you'd still go blind almost as fast staring at it.

How about two terriers?

With the sweeping look of the filaments, it looks like a painting by Van Gogh...

Awesome Sunspot!!!

I missed the Eclipse here, and it was cloudy anyway...

:---[===] *

Ludo wrote:If the sunspots are dark because they are cooler than the rest of the sun does it mean if we take a photo encompassing only the region of a sunspot we'd see it more bright?

What I mean is, do we see sunspots as dark because the photo in question adjusted for the brightness of the overall regions of the sun?

Yes! Why don't we ever get a longer exposure on a darker area to show us what is there? I've wondered about that for decades! Thanks for asking!!

Chris Peterson wrote: ...
Sunspots are blazingly bright. If the entire surface of the Sun were the temperature (and brightness) of a sunspot, you'd still go blind almost as fast staring at it.

That's so true, although one might be tempted to think otherwise.
I plotted the blackbody visibility (adjusting for photopic vision sensitivity) for three temperatures: 5800°K (Sun), 3800°K and ~3000°K (latter two for cool sunspots).
The visible energy at 3000°K is ≈1.8% of the visible energy at 5800°K. The APOD shows the central sunspot region also to be ~1.8% of the bright region surrounding the spot. Since the Sun is a good blackbody, it seems reasonable to conclude the coolest sunspot region ~3000°K. This temperature is within the sunspot temperature range. Put in terms of magnitudes, the coolest sunspots appear about 4½ magnitudes fainter, so at 3000°K, the whole sun would be about -22.3 mag.