The full aperture of the telescope was opened on May 21. Already on the next day, May 22, the seeing got good. The very first exposure that was saved on disk was on a sunspot group. It demonstrated in a dramatic way that the telescope produced diffraction-limited images. This image was part of the data used for the first scientific publication (link) on the discovery of dark cores in penumbral filaments - which was  published in Nature  later in 2002.  

During the two decades that have passed since then, the SST has acquired several advanced instruments. It has thus been able to stay on the frontline of solar research and its publication list is continuously growing.

Happy birthday SST! 

A composite image of an active region containing several sunspots and pores taken with SST.
The first observation done with the SST, depicting the active region AR9957 containing several sunspots and pores taken during May the 22nd, 2002. Note that the image has not been subject of any of the image reconstruction techniques that now are standard.