DISTRIBUTION OF ORGANIC SUBSTANCES I17 



carbons form one of the chief types of carbon compounds 

 in the atmospheres of these as of other stars. 



Our Sun is classified as a star of type G (yellow stars). The 

 temperature of the atmosphere of the Stm is about 6,000° C. 

 The temperature of the outer layers is as low as 5,000° C, 

 while the innermost parts accessible to investigation reach 

 7,000° C. Spectroscopic studies show that even here a con- 

 siderable proportion of the carbon is present in the form of 

 compounds ^vith hydrogen (in the form of methyn, ch), and 

 there may also be more complicated compounds containing 

 several atoms of carbon and hydrogen. ^^ 



We thus see that compounds of carbon and hydrogen — 

 hydrocarbons — are very widely distributed in the atmospheres 

 of stars of various types. It is, however, clear that they must 

 have been formed abiogenically as there can be no question 

 of any vital processes taking place at temperatures of some 

 thousands of degrees, such as prevail on the surfaces of stars. 



This wide distribution of hydrocarbons is also fotmd at 

 the other extreme of temperature within the universe, at 

 temperatures approaching absolute zero. 



It is now well known that by no means all the matter of 

 our galaxy and other analogous systems exists in the form 

 of large aggregates such as stars and planets. A considerable 

 part of its mass (10 per cent or maybe far more) is scattered 

 through space in the form of very finely divided dust or 

 gas.^^ Clouds of cosmic dust are mainly concentrated in the 

 plane of the galaxy. Some of these are visible to the naked 

 eye, sharply outlined against the light background of the 

 Milky Way by virtue of their absorption of light. 



It may be easily shown spectroscopically that atoms and 

 electrons in the interstellar gas in the neighbourhood of stars 

 of types O and B can attain very high speeds, corresponding 

 to temperatures of several thousands of degiees. In those 

 parts of interstellar space which are far away from hot stars 

 there are wide areas in which hydrogen exists in the un- 

 ionised form, the temperature of the gas in these areas 

 being no more than 50° - 100° Absolute (about —200° C). 

 This was established by direct measurement using radio 

 waves. ^® The temperature of the cosmic dust is even lower. 

 It never rises more than a few degrees above absolute zero. 



