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Page:Popular Science Monthly Volume 57.djvu/657

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CHAPTERS ON THE STARS.
A B
Position (1), stars at pericenter * *
Interval, 16 hours.
Position (2), A eclipses B *
Interval, 20 hours.
B A
Postion (3), stars at apocenter * *
Interval, 20 hours.
Position (4), B eclipses A *
Interval, 16 hours.
Position (1) is repeated * *

U Pegasi is a star which proved as perplexing as Tau Cygni. It was first supposed to be of the Algol type, with a period of about two days. Then it was found that a number of minima occurred during this period, and that the actual interval between them was only a few hours. The great difficulty in the case arises from the minuteness of the variation, which is but little more than half a magnitude between the extremes. The observations of Wendell, at the Harvard Observatory, with the polarizing photometer, enabled Pickering to reach a conclusion

PSM V57 D657 Light curve of the u pegasi.png

Fig. 3. Light Curve or U Pegasi, of the Beta Lyræ Type, from Observations by Wendell at the Harvard Observatory. Magnitude at Maximum, 9.32; at Principal Minimum, 9.90; at Secondary Minimum, 9.76. Period, 9 hours.

which, though it may still be open to some doubt, seems to be the most likely yet attainable. The star is of the Beta Lyræ type; its complete period is 8 hours 59 minutes 41 seconds, or 19 seconds less than nine hours; during this period it passes through two equal maxima, each of magnitude 9.3, and two unequal minima 9.76 and 9.9, alternately.

The difference of these minima, 0m. 14, is less than the errors which really ordinarily affect measures of a star's magnitude with the best photometers. Some skepticism has, therefore, been felt as to the reality of the difference which, if it does not exist, would reduce the periodic time below four and one-half hours, the shortest yet known.