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This is a classic trick question.
Ask a friend, "what is the closest star?" and then watch as they try to recall some
nearby stars.
Sirius maybe? Alpha something or other? Betelgeuse?
The answer, obviously, is the Sun; that massive ball of plasma located a mere one-hundred-and-fifty
million km from Earth.
Let's be more precise; what's the closest star to the Sun?
You might have heard that it's Alpha Centauri, the third brightest star in the sky, just
four-point-three-seven light-years from Earth.
But Alpha Centauri isn't one star, it's a system of three stars.
First, there is a binary pair, orbiting a common center of gravity every eighty years.
Alpha Centauri A is just a little more massive and brighter than the Sun, and Alpha Centauri
B is slightly less massive than the Sun.
Then there's a third member of this system, the faint red dwarf star, Proxima Centauri.
It's the closest star to our Sun, located just a short four-point-two-four light-years
away.
Alpha Centauri is located in the Centaurus constellation, which is only visible in the
Southern Hemisphere.
Unfortunately, even if you can see the system, you can't see Proxima Centauri.
It's so dim, you need a need a reasonably powerful telescope to resolve it.
Let's get sense of scale for just how far away Proxima Centauri really is.
Think about the distance from the Earth to Pluto.
NASA's New Horizons spacecraft travels at nearly sixty-thousand-kilometers-per-hour,
the fastest a spacecraft has *ever* traveled in the Solar System.
It will have taken more than nine years to make this journey when it arrives in twenty-fifteen.
Travelling at this speed, to get to Proxima Centauri, it would take New Horizons seventy-eight-thousand
years.
For those of us in the Northern Hemisphere, the closest visible star is Barnard's Star,
another red dwarf in the constellation Ophiuchus.
Unfortunately, just like Proxima Centauri, it's too dim to see with the unaided eye.
The closest star that you can see with the naked eye in the Northern Hemisphere is Sirius,
the Dog Star.
Sirius, has twice the mass and is almost twice the size of the Sun, and it's the brightest
star in the sky.
Located eight-point-six light-years away in the constellation Canis Major - it's very
familiar as the bright star chasing Orion across the night sky in Winter.
So remember, the closest star to the Sun is Proxima Centauri, and the closest star you
can see from the Northern Hemisphere is Sirius.
And if someone ever asks you "What's the closest star to the Earth", you know what
to do.