Fig8_1 Original Hertzsprung-Russell diagram

Fig8_1 Original Hertzsprung-Russell diagram

Fig. 8.1 . The absolute luminosity, in magnitude units (vertical axis) plotted in 1914 by Henry Norris Russell (1877?1957) as a function of spectral class (top horizontal axis) for four moving star clusters: the Hyades (black dots); the Ursa Major group (small crosses), the large group in Scorpius (small open circles), and the 61 Cygni group (triangles). The large circles and crosses represent points calculated from the mean parallaxes and magnitudes of other groups of stars. The two diagonal lines mark the boundaries of Ejnar Hertzsprung’s (1873?1967) observations of the Pleiades and Hyades open star clusters in 1911; this is now known as the main sequence along which most stars, including the Sun, are located. The giant stars are located at the upper right. In his publication, Russell included a very similar diagram for individual bright stars whose distances had been established from stellar parallax measurements, it closely resembled the diagram shown here with an exceptional point in the lower left-hand corner, which we included here with an x mark. This star is the faint companion of a double-star system Omicron2 Eridani, or 40 Eridani, now known to be a white dwarf star. [Adapted from Henry Norris Russell, Relations between the spectra and other characteristics of stars, Popular Astronomy 22, 275-294 (1914).]

Copyright 2010, Professor Kenneth R. Lang, Tufts University