Hi Kevin

Sunspots are region of very strong magnetic fields. Generally, the atmosphere at the surface of the Sun (the photosphere) is at about 5800 Kelvin (10,000 Degrees Fahrenheit). The magnetic field causes the photosphere to be cooler at the sunspot location (~4000 Kelvin).

How bright it looks depends very,very sensitively on the temperature, so the sunspots look dark compared to the hotter surrounding photosphere.

So sunspots are not "black", just much darker than their surroundings. They only look "black" because the image is taken at an exposure optimized to see the hot photosphere. Sometime we seen areas around sunspots that are brighter; this means they are hotter.

Hope this helps

Paulett

Hi - the image I've linked to here (too big for this post - go to http://www.spaceweather.com/images2011/18oct11/hmi4096_blank.jpg) is today's image of the Sun from the HMI instrument aboard the Solar Dynamics Observatory. Look at the full image, and zoom in on one of the sunspots. The dark part of a spot is the umbra, the less-dark area is called the penumbra. The umbra has the strongest and most homogeneous magnetic field; pretty much 3000G +/- 500, and pretty much going directly outward from the "solar surface". The penumbra, on the other hand, is made up of fine strands, some very inclined and lying close to the solar surface, some less inclined and heading up into the corona; some stronger and some weaker, but generally around 1000G. The structure in the penumbra has been likened to two combs (like for your hair) shoved together with some tines going horizontally, the others going vertically, in between each other.

At high resolution, you can see how much fine structure there is: http://www.nsf.gov/news/n...d=104508&org=NSF

At lower spatial resolution there's some blurring, and the dark- and bright- small structures just look middle-bright between the dark umbra and the brighter photosphere outside of the sunspot. But the penumbra is really very interesting and exactly why and how it forms is still pretty much unknown.

Cheers, -KD