I'm up early... so here's a crapload of info you probably don't want to know.
The star Betelgeuse is a red giant in the Orion constellation. It's the bright orangish one a short distance above the belt.... the second brightest in the constellation. To give you an idea of the size of the star, lets say we stick it at the center of our own solar system. It would extend far beyond earth

The fact that it is also the eighth brightest star visible to us on earth also lends some significance to the fact that it may soon go supernova. Now, granted, the collapse of a star has never been fully documented, so the subtleties of collapse are as of yet unknown(For sure of course... we have ideas) to scientists, but we do know that it is beginning. Now, a lot of people point to videos of it's surface activity, which, to those who do not know what they are looking at, may seem to be strongly in support of the theory that the star will soon go boom.
However, this is not the case. The issue is not the surface activity of the star (Considering expansion and retraction of the star itself is normal for a PV star.
The issue is the Loss of mass, which is a significant warning sign that a star is about to go boom. If you're curious as to why, here's a scenario.
Now, stars are large. Infinitely large.
I for one could not imagine the size of something larger than even our own planet.
As you most likely know, stars are giant furnaces, and as we all know, furnaces require energy to make heat.
Stars mostly produce said energy through a process called Thermonuclear Fusion.
Stars will burn for billions of years... and take even longer to form

But, when a star becomes old, and I won't go into detail, because that would take some time to explain... The star begins to gain mass, from the fusion of elements at it's core. Now, the larger the star becomes, the cooler it becomes. This is because as stars grow larger, they consume more energy. Now, when that energy consumption surpasses the energy produced by the splitting of nuclei in Thermo-Nuclear Fusion, the star begins to lose mass.
When a star loses enough mass, the gravitational pull of the core will eventually cause a collapse. If the core is too large, over something called the Chandrasekhar Limit, then the star will form either a Neutron Star(Pulsar), Type 1b-1c, or Type II Supernova.
Now, scientists also have another fear... that the star will form a black hole.
While I'm not yet versed in the exact science of their formation (Nor are scientists 100% sure how or why they form), there would be no plausible effect on our galaxy from it's formation.
Now, if said black hole were to consume another star... well, that's something I'll explain if prodded into it.
Anyways.
Some examples of what we might see?
Go look at the Crab Nebula. There's a pulsar in the middle of it...
Anyways, there's all the info and more you probably want on Betelgeuse.
But did you know, that there are more supernovae likely to occur within the same time frame as Betelgeuse?
Like VY Canis Majoris... the largest known star in the visible universe.
How big you ask?
[ame=http://www.youtube.com/watch?v=HEheh1BH34Q]Pretty Freaking Huge.[/ame]