Stars similar to the Sun end their lives as white dwarfs. But, before becoming those dense stellar corpses, they expel their outer gaseous layers and they ornate the sky for some thousands of years with the most beautiful objects in the universe: planetary nebulae. M97, better known as Owl Nebula, belongs to this category.

Owl Nebula was discovered in 1781 by Pierre Méchain, a collaborator of Charles Messier, and it was incorporated into Messier's catalog of diffuse objects with the number 97. Although its surface brightness is quite low, it can be seen with amateur telescopes in dark nights. Large telescopes, or photographic techniques, are required in order to perceive the two cavities that justify its name. Only photographs reveal the surprising display of colors of M 97.

The planetary nebula M 97 is placed in the constellation of the Big Bear (Ursa Major). It is very difficult to evaluate the distances to planetary nebulae and this case is no exception. Thus, astronomical literature registers distances ranging from 1500 to 2500 light-years from Earth.

The central, dying star, is a small and hot object, around one hundred thousand centigrade degrees at the surface. The radiations from this white dwarf excite the atoms of the nebulous layers and make them shine. As other planetary nebulae, the shine of M 97 comes mainly from the emissions from ionized hydrogen and oxygen atoms, what gives these objects their dominant reddish and greenish hues. But this object also has a considerable portion of light from the white dwarf that has been reflected by nebular particles. This mechanism makes its color bluer, and distinguishes this from other planetaries with a smaller reflection component.