Dec 4, 2025 · On the basis of appearance, nebulae can be divided into two broad classes: dark nebulae and bright nebulae. Dark nebulae appear as irregularly shaped black patches in the sky and blot out …

Nov 13, 2025 · planetary nebula, any of a class of bright nebulae that are expanding shells of luminous gas expelled by dying stars.

Nov 27, 2025 · Each of these classes is subclassified into three types according to the size of the nucleus and the degree to which the spiral arms are coiled. The three types are denoted with the …

Nov 27, 2025 · During the early 1920s astronomers were divided. Although some deduced that spiral nebulae were actually extragalactic star systems, there was evidence that convinced many that such …

Nov 3, 2025 · On the basis of appearance, nebulae can be divided into two broad classes: dark nebulae and bright nebulae. Dark nebulae appear as irregularly shaped black patches in the sky and blot out …

For historical reasons, nebulae in which hydrogen is mainly ionized (H+) are called H II regions, or diffuse nebulae; those in which hydrogen is mainly neutral are designated H I regions; and those in …

The famous nebulosity in the Pleiades star cluster is of this type; it was discovered in 1912 that the spectrum of this nebula mimics the absorption lines of the nearby stars, whereas bright nebulae that …

Dec 7, 2025 · The remnants of this explosion are visible today as the Crab Nebula, which is composed of glowing ejecta of gases flying outward in an irregular fashion and a rapidly spinning, pulsating …

Dec 8, 2025 · Most are clusters of stars, 35 are galaxies, and 11 are nebulae. Even today many of these objects are commonly referred to by their Messier catalog number; M20, for instance, is the great …

On the basis of appearance, nebulae can be divided into two broad classes: dark nebulae and bright nebulae. Dark nebulae block the light of the stars that lie beyond them and appear as irregularly …