Complex sentence: Muphrid and Arcturus lie only 3.3 light years away from each other, the former would have a visual magnitude -2½ when viewed from the latter and Arcturus would be around visual magnitude -4½ seen from Muphrid.
Split into simpler sentences: Muphrid and Arcturus lie only 3.3 light years away from each other. Viewed from Arcturus, Muphrid would have a visual magnitude of -2½, while Arcturus would be around visual magnitude -4½ when seen from Muphrid.