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The Spectra of Variable Stars

March 31, 1903 — Department of Astronomy, Brooklyn Institute, Art Gallery, Brooklyn NY


In looking at the spectra of the hundreds of thousands of stars that rain down their lights in the Harvard camera what most strikes the observer with wonder is the manner in which these hundreds of thousands conform to about six types.

And then, from night to night and from year to year, one sees each painted line making its faithful imprint, one comes to feel that the types are as constant as the stars themselves, changing only with aeons of evolutions.

But there are some special cases of great and sudden variation, and in these cases lies hidden the key to many of the profoundest secrets of astronomy.

The simplest change shown in variable spectra is the doubling of the lines in spectroscopic binaries. These are double stars so close together that no telescope could resolve them, but they betray their duplicity to the spectroscope.

Photographs of Aurigae, taken at Harvard in the Henry Draper Memorial work, showed that the lines of its spectrum were double every other night and single on alternate nights. This doubling takes place as if by clockwork.

Therefore, it can only be explained on an hypothesis of revolution — twin suns are circling about one another with inconceivable velocity, their combined motion, as seen in the spectroscope, being 150 miles a second, and completing a revolution in four days — or rather, three days, twenty-three hours and thirty-seven minutes.

From the spectroscope it is found that they are 8,000,000 miles apart, a little more than one-fourth of Mercury’s distance from the sun, and their combined mass is four and a half times that of the sun. These values are only true in case the orbit coincides with the line of sight.

[Equal wonders were noted for many other stars and peculiarities of spectra carefully explained, much being said of Nova Persei and of certain nebula. In conclusion, Miss Maury said she had presented some of the cosmic problems suggested by variable star-spectra.]

We can only say that when we thoroughly understand their changes we shall know much more than we do about the heavens and the earth.



Source: The Brooklyn Citizen, April 1, 1903, p. 8.