The Nucleosome has an approximate two fold axis of symmetry which is called the Dyad Axis. So when you rotate the Nucleosome by 180 degree you would observe the similar view of Nucleosome before the rotation.
In a nucleosome, DNA is wrapped around a core of proteins called histones (H2A, H2B, H3 and H4). Another histone H1 links these nucleosome cores together.