Explore the Universe - Zeta Ursae Majoris/80 Ursae Majoris

Last Thursday the sky cleared later in the evening and I had the opportunity to check out some double stars after 11pm.  One of the most famous multiple star systems is Mizar (Zeta Ursae Majoris) and Alcor (80 Ursae Majoris).  These two naked eye stars form the second 'star' in the handle of the Big Dipper.  With decent eyesight you can resolve the separation between the stars with just your eyes.  The next time you look at the Big Dipper look at the second star and see if you can see two.

The names of Mizar and Alcor derive from Arabic with Mizar meaning wrapping or covering and Alcor meaning the neglected one.

There is a Latin saying "Vidit Alcor, at non lunam plenam" which is translated as he saw Alcor, but not the Full Moon.  This is someone who frets over minuscule details but misses the big picture.

Through a telescope Mizar will appear as two visual stars separated by approximately 15".  There has been recent research (2009) that indicates these stars form a sextuple star system with each visual star having a spectroscopic binary.  When I first learned about these stars as a child they were always referred to as an optical double: not gravitationally linked but coincidentally in a common line of sight.  The observing record of this system is shown below.

Zeta Ursae Majoris / 80 Ursae Majoris Observation Record

Tomorrow evening the Moon will be full.  This is the best opportunity to see the ejecta lines from ancient impacts that created the craters.  Any pair of binoculars will show these violent scars across the surface of the Moon.  Stay tuned for more events this month with another open house at the Rothney Astrophysical Observatory!