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Matrix Software > Learng Astrology > Astrophysical Directions > Galactic Objects > Long Period & Variables

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Back to Galactic Objects   |   Back to Astrophysical Direction 

Long Period & Semi-Regular Variables

Long-Period Variables

The Long-period variables, as their name suggests, have periods that range from ninety days up to six or seven hundred. They have spectra of Classes M, S, R, and N, -- the coolest stars -- and large light ranges (from between three to six magnitudes). They are very common in our galaxy, which contain 100,000 such stars. Perhaps the most famous of the long-period variables is Mira Ceti, "the Wonderful", which has been known for centuries. These stars are rare or never found in globular clusters.


Semi-Regular Variables

The semi-regular red variables form a group that grades into the long period variables. They have similar periods and spectra, but their ranges of brightness and their spectral class are much smaller. These stars may be considered cyclic rather than periodic. The lengths of individual cycles and the forms of individual light variations are much more irregular than for the long-period variables, which in turn are less regular than the Cepheids. The semi-regular red variables may be on the verge of becoming long-period variables. This group contains a number of super-giant M stars, such as Betelgeuse and Antares, with absolute visual magnitudes near 4 and a large enough angular diameter to be measured with the interferometer.


Copyright (c) 1997-99 Michael Erlewine


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