"It is now clear that astronomers came across indirect manifestations of the CMB long before the 1960s. In 1941, Andrew McKellar discovered cyanide molecules (HCN) in interstellar space. ... As the object of research, McKellar chose absorption lines caused by cyanide molecules in the star 'ε' of Ophiuchis. He concluded that these lines could only be caused by absorption of light by rotating molecules. Relatively simple calculations allowed McKellar to conclude that the excitation of rotational degrees of freedom of cyanide molecules required the presence of external radiation with an effective temperature of 2.3 K. Neither McKellar himself, nor anyone else, suspected that he had stumbled on a manifestation of the cosmic microwave background."