How do you determine the size of a sunspot region?
The area of sunspot groups is expressed in “millionths of a solar hemisphere” (MH), with 1000MH corresponding to 3.043,7 million square kilometers. This means that a sunspot group which has an area coverage of 1870MH covers 0.187% of the earth-facing solar surface. Most sunspot groups cover an area about the size of the surface of the Earth (which equals almost 170MH) but the larger sunspot groups can easily reach 1000MH or even much more than that.
Image: Sunspot region 11944 at a size of 1480MH as seen by the Solar Dynamics Observatory. The Earth has been added for scale.
Solar area conversion table
| Millionths of Hemisphere | Square kilometers | Square Degrees |
|---|---|---|
| 10 | 30 million | 0.2 |
| 100 | 304 million | 2.1 |
| 250 | 760 million | 5.2 |
| 600 | 1826 million | 12.4 |
| 1200 | 3652 million | 24.7 |
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Space weather facts
| Last X-flare | 2025/12/01 | X1.9 |
| Last M-flare | 2025/12/04 | M6.0 |
| Last geomagnetic storm | 2025/12/04 | Kp5 (G1) |
| Spotless days | |
|---|---|
| Last spotless day | 2022/06/08 |
| Monthly mean Sunspot Number | |
|---|---|
| October 2025 | 114.6 -15.2 |
| December 2025 | 186 +71.4 |
| Last 30 days | 106.3 +12.6 |