Mizar and Alcor

[DarkerSky]

With Ursa Major overhead in early spring, the Mizar and Alcor system is a wonderful sight in any sized instrument - or even with the naked eye.

Look up overhead and locate the second from last of the brightest stars in the tail of the Great Bear. This is Mizar. Look closely from a site with limiting magnitude of better than 4.0 and you should make out a 2nd star of 4th magnitude slightly beneath and to the side of Mizar. This second star is Alcor - a naked eye visual double. The separation is 11' arc minutes.

There is some debate as to whether Alcor and Mizar are gravitationally linked. Some say yes, some say no. Hipparcos puts the distance of Mizar at 78.2 light years, and the distance of Alcor at 81.2 light years. So, if those figures are correct, the real distance between the stars is 3 light years - comparable to the distance between our Sun and Alpha Centauri! That would be some gravitaional link!

In my 8.5" Scope with low power of x63 magnification and a true FOV of just over 1 degrees, the Mizar Alcor system is spectacular. Mizar A shines a bright white with a hint of blue at Mag 2.1. Mizar B is 14" arc seconds away at a PA of 150 degrees and shines white at Mag 4.2. Alcor is in the same FOV, and the starfield around them is rich.

Here is a sketch

8.5" Scope

Mag x63

FOV 1.08 degrees

23.00 to 23.25 UT on 15 March 2010

[astoc]

I always love splitting this double. Nice sketch

John

[Leegsi]

Isnt there another star there too (A double double)?

[astoc]

I think Mizar itself is a double double, but the doubles of A and B are spectroscopic. Alcor is a double, not sure if its spectroscopic or not.

John

[lunator]

At present it is said that Mizar is a spectroscopic double but Alcor isn't.

Alcor has proved tricky to pin down and this could change again

Cheers

Ian

[Astorix]

Very nice sketch:)

[Iris]

<snip> ....

There is some debate as to whether Alcor and Mizar are gravitationally linked. Some say yes, some say no. ...<snip>

The University of Rochester seems to think it has resolved () the issue...

First known binary star is discovered to be a triplet, quadruplet, quintuplet, sextuplet system

First Known Binary Star is Discovered to be a <strike >Triplet</strike>, <strike>Quadruplet</strike>, <strike>Quintuplet</strike>, Sextuplet System : University of Rochester News

[Doc]

Lovely sketch Seb, it's strange I observe this are everytime I observe as it's where I polar align the scope, but have never truly observed and sketched it.