COMPOSITION AND SPECTROSCOPY

The spectroscope has the goal of analysing starlight or other objects in the sky. As all gas heated at high temperatures emits light, it correspond there fore to a spectrum of a light rays (black spectrum with rays of different colours). This shows that the gas will be emitted in different wavelengths. Now, le spectrum of light rays of a chemical element corresponds to the spectrum of absorption of this one. The spectrums are obtained by decomposing the light using a prism or a grating ( this support is composed of numerous parallel tracts ).

There are several possible spectrums :

- the spectrums of absorption which present black rays, which are in reality the chemicals elements, which make up this object.

- the spectrums of emission which themselves presents a more luminous radiations on a darker background which represent equally the elements which make up this object.

- the continuous spectrums present neither dark rays nor light radiations. They are specific to hot and dense bodies.

This document is a spectrum of M27. It's a negative photography, so emitting rays are black over white :

Near the emitting rays are indicated the differents chemicals species which make up the nebula. So this document permit us it contain at least helium, oxygen, nitrogen and hydrogen on different forms.

 

Equally, with these two documents, we can show that there is oxygen and hydrogen, but in differents quantitites. In effect we can see on the document that hydrogen means more spread than oxygen, and divides on the outline of the nebula, while oxygen is found principally in centre.

Slice to show the density 1 with a H-alpha interferential filter (656 nm)
Slice to show the density 2 with a OIII interferantial filter ( 500 nm)

This measures by spectroscopy are relatively reliable, and particulary if the element is in big quantity. This variability is too the result to the great precision of the cameras CCD used. But we must not confuse the absorption's rays ot the element of earth atmosphere ( oxygen,...) with those of the object studied.