Reflection nebula

With reflection nebula is called in astronomy clouds of interstellar dust ( nebula ), which " reflect " the light of neighboring stars, but strictly speaking scatter.

The stars are not hot enough to ionize the material as emission nebulae, so do not cause self-illumination of the nebula. Instead, the starlight is scattered by the smoke particles, microscopic, therefore the fog itself is visible at all only for us. The spectrum of the reflection nebula therefore resembles that of the irradiating star. Among the fog particles are many carbon compounds ( among others diamond dust), but also those of other elements, especially iron and nickel. The latter often align themselves with the galactic magnetic field and thus cause a slight polarization of the scattered light ( James B. Kaler, 1998). The distinction between the two types of fog goes back Edwin Hubble (1922 ).

Reflection nebulae usually appear blue because blue light is scattered more strongly than red light. A similar effect, responsible for the blue color of the sky.

Reflection and emission nebulae are often seen together and are sometimes collectively referred to as diffuse nebulae. Examples of these are the Omega Nebula M17 and the Orion Nebula M 42

Approx. 500 reflection nebulae are known. Especially gorgeous are the bluish reflection nebulae, which are located around the stars of the Pleiades M 45. Also the blue reflection nebula appears at the northern edge of the Trifidnebels M 20 The red giant Antares is surrounded by large red reflection nebula Ced 132.

Hubble published in 1922 the results of his studies of gaseous nebulae (English bright nebulae ). Part of this work is the Hubble luminosity law for reflection nebulae (English Hubble luminosity law for reflection nebulae ), which establishes a relationship between the apparent size of the nebula and the apparent brightness of the star's associates:

Where is a constant that depends on the sensitivity of the measuring instruments.