The electron probability density dristribution in this atom (state: n=2, l=1, m=0) takes the form of "caps" symmetrically located on either side of the nucleus (not shown).

Opposing cap-like structures dominate the morphology of the planetary nebula NGC 6563.

Another example of the class of planetary nebulae characterized by symmetric "caps" morphology; this is NGC 6058.

Source:R. Eisberg and R. Resnick, Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, 2nd ed., John Wiley and Sons, New York, 1985, Fig. 7-10, pg. 251.

Source:G.A. Gurzadyan, Physics and Dynamics of Planetary Nebulae, Springer-Verlag, New York, 1997, Plate VII.

Source: Same as image to the immediate left.