His main work during this time was on variable stars.
Only about 55 variable stars have been discovered in the central part of M55.
At least 43 variable stars have been observed within M4.
It is a variable star with a magnitude change of less than 0.02.
Between 1891 and 1920 he made over 250,000 observations of 98 variable stars.
He is primarily noted for his work in the study of variable stars.
He observed and recorded more than 5,000 variable stars during his career.
A variant of this system is used to name variable stars.
She began her training in astronomy as an observer of variable stars.
It has since become a variable star fluctuating between 2.0 and 1.6.