Free Astronomy Magazine July-August 2014

STELLAR EVOLUTION pear very brilliant and thus it should have always been known to man. In- stead, it was discovered only in 1961 under Australian skies by Swedish astronomer Bengt Westerlund, later appointed director of the European Southern Observatory from 1970 to 1974. The reason for such a delay in discovering this cluster must be sought in the fact that it lays perspectively behind a huge complex of interstellar gas and dust that reduces its bright- ness by more than 100,000 times and allows only the brightest stars to shine through (all, however, weaker than mag- nitude 14), which despite being predo- minantly blue appear red, due to the more efficient absorption of blue wave- lengths by the interposed obstacle. From the discovery of that cluster, some decades had to go by before astronomers had the proper instru- ments to fully appreciate the impor- tance of that structure in the study of stellar evolution. In the meantime, the W ide-field image of the sky region centred on the open cluster Wd1 in the constella- tion Ara. The light of the stars making up the cluster appears strongly redden- ed due to the presence of gas and dust. With- out them, it would be a very brilliant struc- ture. The box encircles the en- larged area seen below, where a second frame indicates the confines of the image shown on the next page. [ESO/Digitized Sky Survey 2]