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 kilometres. 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.

Sunspot region 11944 compared with Earth

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 Kilometres Square Degrees
10 30.4 million 0.2
100 304.3 million 2.1
250 760.9 million 5.2
600 1826.2 million 12.4
1200 3652.4 million 24.7

<< Go to previous page

Current data suggest that it is not possible to see aurora now at middle latitudes
G2 - Moderate geomagnetic storm
Observed Kp: 6-
The solar wind speed is currently moderately high (639.4 km/sec.)
The direction of the interplanetary magnetic field is slightly South (-7.34nT).
The maximum X-ray flux of the past two hours is:

Latest news

Today's space weather

Auroral activity Minor Severe
High latitude 20% 30%
Middle latitude 25% 10%
Predicted Kp max 5
Solar activity
M-class solar flare 1%
X-class solar flare 1%
Moon phase
New Moon


A lot of people come to SpaceWeatherLive to follow the Sun's activity or if there is aurora to be seen, but with more traffic comes higher server costs. Consider a donation if you enjoy SpaceWeatherLive so we can keep the website online!


Get instant alerts!

Space weather facts

Last X-flare:2015/05/05X2.7
Last M-flare:2016/11/29M1.2
Last geomagnetic storm:2017/03/22Kp5 (G1)
Number of spotless days in 2017:27
Last spotless day:2017/03/20

This day in history*

Solar flares
*since 1994