Nebula

As fog ( OHG nebul about Latin nebula of gr νεφέλη nephele or νέφος nephos, cloud ') or nebulae all bright -dimensional objects were originally referred to the celestial sphere in astronomy. This included Nebula, ie galaxies ( spiral nebula ) and star clusters, since they appear as nebulae at low resolution in the telescope or with the naked eye. Some of the proper names of such objects have kept themselves, such as the Andromeda Nebula M 31 or the Triangulum Galaxy M33

Today, the term cosmic fog but is used almost exclusively for interstellar clouds of dust and gas, which are divided into different categories depending on the nature of their luminosity: gaseous nebulae that emit or reflect light, dark nebulae, or galaxies (formerly known as spiral nebulae called ).

The first systematic directory foggy sky objects is the 1774 created by Charles Messier Messier catalog. Another important directory is the New General Catalogue (NGC ) by Johan Ludvig Emil Dreyer ( 1888). Both as well as gas and dust nebulae also contain galaxies and star clusters, and are still used today.

Most important of fog

  • Emission nebulae excited by the light of hot stars that emit light itself, such as the Orion Nebula M 42
  • Planetary nebulae in which the cast-off gas envelopes of a hot star are excited by this to light, such as the Ring Nebula M57 in Lyra
  • Supernova remnants, the high speed of the interstellar matter encountered and thereby lights placed gas shells that were thrown in the supernova of a star, such as the Crab Nebula M1
  • Occasionally dark clouds ( dark nebulae ) that absorb the light located behind objects, so do not light up, such as the Horsehead Nebula B33
  • Except Galactic Nebula: These are all galaxies. Best known is the Andromeda Galaxy M31, which is about as big as our galaxy 2.3 million light years away.

Also, as fog is referred to in the astronomy of the solar nebula, the gas cloud from which our solar system probably has formed. In contrast, the clusters are no longer referred to as fog, even if they appear to be in small scopes.

In the fog escape is increasing with the distance exodus of extragalactic stellar systems ( galaxies).

Observation

Visually, the fog objects are limited observable, because the surface brightness to our eyes is often too low. Helpful is the method of indirect vision, in which the object is not directly fixed, but looks just past it.

The astrophotography, however, can also depict very faint nebula, because the photographic plate or CCD sensor can be exposed for a long time - see the images to the Orion Nebula or the Andromeda galaxy.

362275
de