Tables 633-53S. 



ASTRONOMICAL DATA. 



TABLE 533. — Stellar Spectra and Related Characteristics. 



411 



The spectra of almost all the stars can be arranged in a continuous sequence, the various types connected m a series 

 of imperceptible gradations. With one unimportant exception, the sequence is linear, the transition between two given 

 types always involving the same intermediate steps. According to the now generally adopted Harvard system of 

 classification, certain principal types of spectrum are designated by letters, — O B, A, F, G, K, M, R and N, — and 

 the intermediate types by suffixed numbers. A spectrum halfway between classes B and A is denoted B5, while those 

 differing slightly from Class A in the direction of Class B are called B8 or Bg. In Classes M and O the notation Ma, 

 Mb Mc, etc., is employed. Classes R and N apparently form a side chain branching from the main series near Class K. 



The colors of the stars, the degree to which they are concentrated into the region of the sky, including the Milky 

 Way, and the average magnitudes of their peculiar velocities in space, referred to the center of gravity of the naked- 

 eye stars as a whole, all show important correlations with the spectral type. In the case of colors, the correlation is 

 so close as to indicate that both spectrum and color depend almost entirely on the surface temperature of the stars. 

 The correlation in the other two cases, though statistically important, is by no means as close. 



Examples of all classes from O to M are found among the bright stars. The brightest star of Class N is of magni- 

 tude 5.3; the brightest of Class R, 7.0. 



TABLE 534. — The Harvard Spectral Classification. 



Compiled mainly from the Harvard Annals. Temperatures based on the work of Wilsing and Scheiner. Radial 

 velocities from Campbell. Data for classes R and N from Curtis and Rufus. The color indices are the differences of 

 the visual and photographic magnitudes. Negative values indicate bluish white stars; large positive values, red stars. 

 The peculiar velocities are in the radial direction (towards or from the sun). The average velocities in space should 

 be twice as great. 



The "galactic region" here means the zone between galactic latitudes =*= 30°, and including half the area of the 

 heavens. 



56% of the stars of known spectra belong to classes A, F, G, K, 99. 7% including B and M (limes, 1919). 



TABLE 535. — Apex and Velocity of Solar Motion. 



Smithsonian Tables. 



