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No. 48 - June 2005

Z Ursae Maioris

Z UMa is what is called a semi-regular variable star. Semi-regular variables are post main sequence cool (red) giant and super giant stars. At various levels within this type of star pulsations are generated which interfere with each other. Complex patterns of variability result as the surface of the star contracts and expands.

Four observers in Scotland (three from the ASE) have been studying this star in recent months. The observations of the four, over a 200 day period, have been combined in the following diagram.

light curve

Nearly all these observations have been done with binoculars. The observations illustrate a distinctive light curve which agrees closely with the world wide observations collected by the AAVSO (the American Association of Variable Star Observers). The results are a good example of the valuable work that can still be done by visual amateur astronomers. CCD photometry can be more accurate. Magnitude can be measured to one hundredth of a magnitude compared with one tenth of a magnitude by visual observers. However, CCD photometry would not portray, in this case, a significantly different light curve.


Gary Poyner subjected the results of the 4 observers to an analysis by the Peranso software. This suggests a period of 189 days for the primary pulsation which is quite close to the official period of 195.5 days.

Des Loughney


Cover page

From the President

Cooling the Earth

See the Sun in a different light

The 2005 Scottish Astronomy Weekend

Z Ursae Maioris

The Televue Radian eyepiece

The Society at work and the City Observatory

About the ASE Journal

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