Sunspots size

Jean Aboudarham wanted to send us as often as possible the sizes of the biggest visible sunspots. But he is very busy and couldn't do this all the time. He sent us these datas.



(% of sun diameter)


1164 group :

spot 1

spot 2

spot 3


1.8 %

1.2 %

0.87 %

 Anyway, he gave us a place where we can find useful inforamtions directly on BASS2000 website. The table at the end has got a row called area for every active group (NOAA). This area is the total corrected area of the group in millionths of the solar hemisphere. This can be used to compare to our calculations.


(direct translation of pupils' calculations)

Sunspot size

To find real sunspot size, we must find real Sun's diameter (1392000 km) but also on the screen. Then we measure on the screen the spot's size and we make the calculation.

real Sun's diameter × spot's size on the screen  ÷ Sun's diameter on the screen


Example :

spot n°1166 (march 8th at 8h40) on the screen = 1,6 cm

Sun on the screen = 89 cm

1392000 × 1,6 ÷ 89 = 25025 km. This spot has a diameter twice bigger than Earth's one !


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