Complex sentence: In 1926 he graduated with excellent marks from Svenska normallyceum, a renowned gymnasium in Helsinki for Swedish-speaking boys and in the same year he enrolled at the University of Helsinki, planning to major in astronomy.
Split into simpler sentences: In 1926 he graduated with excellent grades from Svenska normallyceum, a renowned gymnasium in Helsinki for Swedish-speaking boys. In the same year he enrolled at the University of Helsinki, planning to major in astronomy.