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Z Ursae Majoris

Z UMa, known formally as Z Ursae Majoris, is a semi-regular variable located in the upper left of the bowl of the Big Dipper. This star is popular since, due to its +57° declination, it is a circumpolar star for most of the population of the Northern Hemisphere.

Varying between magnitudes 9.0 and 6.8, under dark skies this star can be followed through its cycle with large binoculars. Urban dwellers under severe light pollution will be able to still follow it with a small telescope. It is a popular "first variable star" target.

Z UMa remains interesting in part because of its unusual spectrum, and because observations seem to suggest the star has more than one pulsation cycle - its primary 195.5 day cycle, and an ill-defined 205 day cycle. These cycles may be beating against one another to produce a third cycle of 4200 days.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484