Penumbra (sunspots)

Close up

With penumbra and umbra ( lat. Penumbra and umbra ) are of astronomers those areas within the sunspots called the dark are than the normal solar surface.

Temperatures

The average surface temperature of the sun is almost 6000 ° C (" effective temperature " 5770 Kelvin ). The core area of ​​a sunspot, the umbra (“ umbra ”), is around 2000 K cooler and is therefore around 4000 ° C. Large sunspots also show a penumbra (“ penumbra ”), which has a temperature of 5000 - 5500 ° C. There are numerous individual spots in it (see picture).

The sunspot shows the Wilson effect .

Despite their lower temperature , these sunspot zones are by no means black or gray, but are also to be understood as violently glowing gas . They radiate with around 20 to 70 percent of the normal photosphere . Only the maximum of the radiation has shifted a little from yellow-green to red .

Counting sunspots

The simplest measure of solar activity - which varies in an 11-year cycle and is also subject to weekly and monthly fluctuations - is the so-called sunspot relative number

${\displaystyle R=10\cdot g+f}$

The number f indicates the number of spots (regardless of their size), while g represents the number of groups. As sunspot group include individual spots, but more carry large groups Penumbragebieten to R at.

The sunspots are caused by local disturbances in the sun's magnetic field , which hinder the convective heat transport from the depths.

Remarks

1. ↑ Some small pores can be seen close to the sunspot and many granulations in the background, each 1000 km in diameter.
2. ↑ It appears that the dark umber is deeper in the photosphere than the penumbra. As a result, sunspots look asymmetrical near the edge.