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The temperatures of B stars, although less than that of 0 stars, average more than 20,000 degrees, and the degree of excitation of the atoms in their atmospheres which determines the temperature is slightly less than that of the O-stars. High as these temperatures are they are but surface temperatures. The temperature at the center of an average star has been estimated to be around 40,000,000 degrees. Other well-known blue-white stars of B-type are Bellatrix and Saiph, diagonally opposite each other in the constellation of Orion, and Zeta Tauri, the more southerly of the two stars that mark the tips of the horn of Taurus. Three of the stars in the Southern Cross, Acrux at the top of the Cross, and Beta and Delta, which mark the ends of the cross-arm, are all bluish-white, B-type, or helium stars.

The temperatures of B stars, although less than that of 0 stars, average more than 20,000 degrees, and the degree of excitation of the atoms in their atmospheres which determines the temperature is slightly less than that of the O-stars. High as these temperatures are they are but surface temperatures. The temperature at the center of an average star has been estimated to be around 40,000,000 degrees. Other well-known blue-white stars of B-type are Bellatrix and Saiph, diagonally opposite each other in the constellation of Orion, and Zeta Tauri, the more southerly of the two stars that mark the tips of the horn of Taurus. Three of the stars in the Southern Cross, Acrux at the top of the Cross, and Beta and Delta, which mark the ends of the cross-arm, are all bluish-white, B-type, or helium stars.

Betelgeuse, Antares and Gamma Crucis, at the foot of the Southern Cross, are all red M-type stars. Aldebaran is about on the borderline between a K-type and M-type star, although it appears quite red. Rigel, which has been described both as a bluish-white star and a white star, is on the borderline of the B-type and A-type stars. It also has the letter ” p ” attached to its B8 type, and this stands for peculiarity of spectrum. In this star there are intense radiations of ultra-violet light. It will be interesting to know, in a general way, how stars are classified as to color and spectrum in order to seek out a few well-known bright stars in December skies, and to see how well the colors to be expected from their spectral type agree with those actually observed.