Thirty Her is seen to vary by up to a magnitude or so over the 30 years of observation, with a principal period of 93 days. The scale on the bottom is the "Julian Date" of 2440000 plus the number that appears, where the Julian Date is the number of days since January 1, 4713 BC of the Julian Calendar and is commonly used for variable phenomena in astronomy. JD 2446500 corresponds to March 11, 1986. The left-hand scale expresses the difference between the apparent visual magnitude of 30 Herculis and a nearby comparison star. (From an article in the Publications of the Astronomical Society of the Pacific by J. R. Percy, J. B. Wilson, and G. W. Henry.) |