La nebulosa del Búho (M97, NGC 3587) es uno de los objetos más débiles del catálogo Messier, una de sus 4 nebulosas planetarias y se encuentra en la constelación de la Osa Mayor. Fue descubierta por Méchain en 1781. Se trata de una de las nebulosas planetarias más complejas que podemos observar.
The Owl Nebula (M97, NGC 3587) is one of the fainter objects in Messier's catalog. It is one of the four planetary nebulae in that catalog, and situated in constellation Ursa Major. M97 was discovered by Pierre Méchain on February 16, 1781. Admiral William H. Smyth first classified it as planetary nebulae in 1844. The name "Owl Nebula" goes back to Lord Rosse, who first used it in 1848. In 1866, William Huggins recognized its nature as a gaseous nebula from the observation of its spectrum, where he discovered two spectral lines. M97 is one of the more complex planetary nebulae. Its appearance has been interpreted as that of a cylindrical torus shell (or globe without poles), viewed oblique, so that the projected matter-poor ends of the cylinder correspond to the owl's eyes. This shell is enveloped by a fainter nebula of lower ionization. The mass of the nebula has been estimated to amount 0.15 solar masses, while the 16 mag central star is believed to be of about 0.7 solar masses. Its dynamical age is about 6,000 years. (from Stephen J. Hynes, Planetary Nebulae). As often for planetary nebulae, the Owl is significantly brighter visually than photographically, as most light is emitted in one green spectral line. Its distance is uncertain; the Sky Catalog 2000 has 1,300 light years (400 pc), I.S. Shklovsky 1,430, O'Dell and Kohoutek independently found 1,600 in the early 1960s, Cudworth (1974) 2,600 (our value), Becvar's Atlas Coeli Catalog 7,460, Voroncov-Vel'jaminov published 8,150, Kenneth Glyn Jones gives 10,000, and Kaufmann has 12,000 light years (some of these values quoted from Burnham). The DSSM image of M97 reveals that in the background of this nebula, there are several small nebulous objects, most probably very distant galaxies, the brightest of these objects being superimposed by the brighter star above and slightly left of M97. This brightest background object can be found on many larger-field exposures of the Owl Nebula (also is some of the amateur images in our collection). Taken from MAA.