A possible secular change of the period is investigated for 362 Mira stars. Mean periods and the proportion of stars with increasing and decreasing period were calculated using all available maxima found. The state as it was known in 1938 is compared year by year up until 2013. Analysis of O-C diagrams for the stars shows a rate of change of +6.8 x 10~(-6) days/day, standard error 3.8 x 10~(-6). The mean period over 75 years shows an increase by 0.15 day for the investigated stars, and by 2013 58% of them had an increasing period.
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机译：研究了362个Mira恒星在此期间的长期变化。使用找到的所有可用最大值计算平均周期和随周期增加和减小的恒星比例。直到2013年，每年都对1938年的状态进行比较。对恒星的OC图进行分析后，得出的变化率为+6.8 x 10〜（-6）天/天，标准误为3.8 x 10〜（ -6）。 75年的平均周期显示，被调查恒星增加了0.15天，到2013年，其中58％的恒星增加了。
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