Along with the brown bear, it is one of only two of the eight modern bear species not considered globally threatened with extinction by the IUCN. American black bears often mark trees using their teeth and claws as a form of communication with other bears, a behavior common to many species of bears.
Planetary nebulae are astronomical objects made up primarily of gaseous materials. They are extended in size and fuzzy in appearance, and generally show some degree of symmetry. The nebula is illuminated by a central star, which sometimes is too faint to be seen.
Instead the light is reflected off the dust in the nebula so it is similar to the visible light given off by stars. Planetary nebulae are formed when stars similar to the size of the Sun use up the hydrogen in their core and instead begin fusing hydrogen in an outer shell surrounding the core. This results in them expanding to hundreds of times their original size and becoming red giants.