AIP astronomy picture of the month
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The big sunspot passing the solar disk in September 2000.
(credit: H. Balthasar, AIP)
Reason for selection:
This sunspot (active region AR 9169) was the biggest one of the present
solar cycle so far. Its extension corresponds to more than 100000 km.
Although we are close to the maximum of this solar cycle, sunspots
of this size are rather seldom. Using a protection filter, it was visible
for the human eye without telescope. An image of a that large sunspot
cannot be obtained at a big solar telescope like the Vacuum Tower Telescope
on Tenerife (VTT) in a single exposure; instead several subimages have
been taken and put together as a mosaic.
A special blue filter centered on 430 nm has been used.
For comparison, the size of the whole Earth is given in the image.
(credit: H. Balthasar)