Which star is closest to the Sun?
Many people know the easy answer to this one: Proxima Centauri. This is easy to remember considering the name (if “Proxima” does not ring a bell right away, think of the word “proximity”).
Proxima Centauri is a brown dwarf star 4.24 light-years away. That is very close (and this means this star is very alive right now). For reference, one light-year is 63241 times the distance from the Sun to the Earth (called Astronomical Unit).
But Proxima is not alone. It is orbiting a pair of much bigger and brighter stars, α Centauri A and B. Below you can see a picture of their orbits:
Cannot find Proxima in the picture? That is because it is orbiting its companions very far away. According to the source of the picture, Proxima should be orbiting 4 meters away in the picture. In fact, many people believe Proxima was born separately and later captured by A and B. It is even disscused whether it is really trapped in the orbital influence of A and B.
But will Proxima always be our closest celestial friend? No, because the stars are far from being the still, quiet beings that we see in the sky. (Not to mention that Proxima Centauri will eventually die, although it will leave a remant, which I would still count as a star.)
The Earth rotates and moves around the Sun. But while we dance around the Sun we are also moving within the galaxy. And while it is true that the rest of the stars in the Milky Way orbit with us, even our closest companions eventually drag and shift away.
In the next image (from the Wikipedia article on our closest stars) you can see how the stars come closer and further from the Sun as we move.
Note that for a time α Centauri will be the closest star. This means that our real closest star will be α Centauri A or B depending on their 80-year-long orbit.
Take also notice of the gray area at the lower part of the graph; the outer border of the Oort cloud. That is the true limit of the Solar System, where the gravitational influence of the Sun dies. No object orbits our Sun further from that point. And that is very far away, almost half-way to our closest stars. So no, Voyager 1 has not yet reached the true edge of the Solar System.