Horsehead nebula

Bryce Canyon, a hillside of deciduous trees in autumn, the Overture of 1812, horses, a smiling little girl, Horsehead nebula, rings of Saturn, snow-capped mountain in a forest, palm trees on a Caribbean beach, newborn human infant, looks that pass between couples who have been happily married for 30 years, Ferrari Modena, Quebec City, the late Marian Anderson s voice, Newton s solution of the brachistochrone problem, a fresh pizza Martin Luther King Junior s I Have... 

Within a distance of l kpc from the sun, dense interstellar clouds can be observed optically because they attenuate the light of stars located behind them. Fig. 10 shows as an example the dust clouds Barnard 1968 and 1972 which are seen as dark areas in an otherwise rather uniform field of stars. Fig. 11 shows another dust cloud, the horsehead nebula", silhouetted against the bright background of an emission nebula (HII region). Most of the extended dust clouds... 

Fig. 11. The horsehead nebula, another dust cloud, seen projected against an HII region, i.e. an extended ionized cloud of interstellar gas...

The four nebulae shown here contain a stew of elements. The red color in two of the nebulae is emitted by hydrogen atoms. The Horsehead Nebula can be seen on the right. The fourth nebula is the bluish structure below the horse s head. The round, bright object on the left is the star Zeta Orionis. 

This then requires specific kinetic routes for molecule formation (Herbst and Klemperer, 1973). The specific chemistry requires an energy source since the cloud temperature is 10-20 K. The gas density is near 10 molecules cm and is 99% hydrogen and helimn. The beautiful Horsehead nebula in Orion, a rich molecular region, is shown in Figure 17.3 the molecular cloud Barnard 68 is shown in Figure IV.d.i ... 

These excellent pictures of the dark molecular clouds are readily available. For the Horsehead nebula in Orion, see www.noao.edu/image gallery/html/im0661.html for the molecular cloud Barnard 68, see http //antwrp.gsfc.nasa.gov/apod/ap990511. html. 

The radiation thus produced includes a number of spectral lines, one of the strongest of which is the Balmer alpha line (X = 656.3 nm) in the red region of the visible spectrum. The emission of these red lines is responsible for the brilliant reddish color of HII clouds and also for their common name emission nebulae. In the photograph on page 33, the famous Horsehead Nebula is visible because the dust of... 

The bright emission nebula 1C 434 provides a spectacular background for the cold dust of which the Horsehead Nebula is composed. (European Southern Observatory/Photo... 

This is the well-known Horsehead nebula in the constellation Orion. It is made mostly of dust, plus some cold hydrogen gas, and it stands out in silhouette against a more distant mass of hot, luminous hydrogen. It is similar to the great black rift and the indistinct dark clouds which obscure great sections of the veil of stars in the Milky Way. 

Fig. 2.5 The horsehead nebula, a dark cloud illuminated on its right edge by FUV radiation from the nearby 09 star oOri. This edge is a template source for studying the physical and chemical processes in UV irradiated interstellar matter. The background image is taken in the visible at ESO. The small colour pictures show the distribution in various spectroscopic tracers [31]...

Rimmer PB, Herbst E, Morata O, Roueff E (2012) Observing a column-dependent in dense interstellar sources the case of the horsehead nebula. Astron Astrophys 537 A7. doi 10.1051/ 0004-6361/201117048... 

Figure 6.1 (a) The Horsehead Nebula in the constellation of Orion, (b) Hubble Space... 

In Section 6.2.1 we pointed out that the vibration of a homonuclear diatomic will not be IR active. So where does this leave the spectral bands shown in Figure 6.1 for H2 from the observations of the Horsehead Nebula in the introduction to this chapter ... 

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