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.
Planetary nebulae are shells of gas thrown out by some stars near the end of their lives. Our Sun will probably produce a planetary nebula in about 5 thousand million years. They have nothing at all to do with planets; the terminology was invented because they often look a little like planets in small telescopes.he gas and dust in the nebula emits light because it is irradiated by nearby emerging stars. Located at a distance of about 1,600 light years, the Orion nebula is the brightest diffuse nebula in the sky, visible to the naked eye.