BBC Focus Magazine

[M Paul Lloyd]

One of the wonderful things about astronomy is when things turn out not to be what you thought they were.

"Alcor and Mizar, were the first binary stars ever known. Modern telescopes have since found that Mizar is itself a pair of binaries, revealing what was once thought of as a single star to be four stars orbiting each other. Alcor has been sometimes considered a fifth member of the system, orbiting far away from the Mizar quadruplet.
Now, an astronomer at the University of Rochester and his colleagues have made the surprise discovery that Alcor is also actually two stars, and is apparently gravitationally bound to the Mizar system, making the whole group a sextuplet. This would make the Mizar-Alcor sextuplet the second-nearest such system known. The discovery is especially surprising because Alcor is one of the most studied stars in the sky.

http://www.sciencedaily.com/releases/20 ... 092005.htm

[Liam Sheppard]

do any of these stars have planets?

If so how would the orbits of the suns effect life/weather on these planets?

how close do they orbit each other, what would the sky look like on this planet! Tatooine?

[M Paul Lloyd]

I would suggest that intrinsic planetary orbits would be mostly non-viable iwthin such a complex system Liam, so no Tatooine sorry.

[Liam Sheppard]

would it be possible for a planet to orbit two stars in a figure of 8 orbit?

[M Paul Lloyd]

Sadly no Liam, orbits are defined by a centre of gravity around which particles constantly free fall in one direction along an elliptical path whilst a figure of 8 requires a change of direction and resultant acceleration which would be extremely unlikley even if both stars were of identical mass they would be free falling around each other in exactly the same way so any planet within such a system would end up orbiting one or other of the stars or be doomed to fly off into space, torn to pieces or be consumed by one or other star.

The most likely scenario I can think of is if a planet were to be orbiting say a main sequence star (not unlike our own sun) and that star was in turn orbiting a larger red giant at some considerable distance, well then that might just work.

[Liam Sheppard]

I thought as much...

could you have a massive star, which is orbited by a smaller star.. and on the same plane a planet also orbits... so you have a sun in the sky, and a smaller sun that would be like venus in our sky?

[M Paul Lloyd]

Ok, let's scale up our own solar system, make the sun a red giant and place the earth further out to allow for the greater gravity, then substitute Jupiter with that small star you mentioned at a correspondingly greater distance and yes you would end up with two suns but bear in mind that the different orbits would mean that the small sun would only be in the sky at certain times of the year.

I am not so sure if a smaller star on an inferior orbit, that is say relative to Venus, would work without seriously disrupting the orbits of any outer planets. But I could be wrong it is a rather complicated subject that is not all that well understood.