Mizar/Alcor

[Saxony]

Silly question time :oops:

As most of you know I am new to all this. I thought Mizar/Alcor was a double star, a name for each of them, but now I believe that Mizar is now a double star and Alcor is just close by, is this correct?

I tried googleing but got even more confused with double stars/binary stars/spectroscopy (what ever that is), so second silly question, what is a double star? Why is it different to a binary star?

Am I correct in thinking a binary star is two stars that orbit each other? (Although I can't quite figure that out :shock: ) A double star is two stars that are in the same place but one is alot further out, if you see what I mean?

It would be nice to hear in laymans terms any info that might help me understand lol.

Sax

[daz]

Mizar and Alcor are forever linked because they are so close. Mizar is the larger, Alor the smaller.

If memory serves, they are both doubles.

A double star is when two stars are so close together, they visually appear as one. They can be just optically doubles, as opposed to physical doubles - i.e. its a line of sight coincidence.

A binary star are two stars orbiting a common centre of gravity, as you thought.

Make sense?

[mdstuart]

This explains it well.

http://www.astro.uiuc.edu/~kaler/sow/mizar.html

[daz]

And just change the last bit to alcor.html for the Alcor page

[Saxony]

So have I got this right, from the link posted? Mizar has in fact got a couple of double stars that orbit around it?

The double stars orbit each other, then those two double stars orbit around Mizar and Alco and mizor also orbit each other.

Also I read double stars are two stars orbiting around their centre of mass? What is their centre of mass?

Sorry I feel really dumb asking, but trying to learn. To me, their centre of mass would be the middle of them so I assume they just orbit each other? I guess if one is bigger they orbit faster or if one is further away or something, sorry never paid much attention in physics maybe I should have. :crybaby:

Gosh I am confussed not sure even I understand what I have wrote let alone you guys :oops:

[barkis]

I believe Mizar and Alcor, the pair easily spotted in a scope, were a test for good eyesight. They are not physically bound, but are moving through space together, they are just an optical binary.

Mizar is a four star system as I understrand it. The companions are only detectable spectroscopically. Lunator is more likely to explain the system better to you.

Ron.