[MUSIC]
This is the story of two
stars that are red supergiants.
And when people call a start red, they
usually mean kind of orange — kind of like you.
There's nothing too special about
a star being red — most stars are red.
In fact, in our neighborhood in the
galaxy, seven out of 10 stars are red stars.
But most red stars are very faint
and you'd need a telescope to see them.
They're called red dwarf stars, and a
good example of that is Barnard's star here.
When we compare Barnard's Star to the
Sun, we can see why a star like this is so dim.
And this is not an actual photograph of Barnard's Star.
In a telescope, all stars, except
for the Sun, are just specks of light,
so we have no direct knowledge of
the surface, except for the Sun itself.
In about five billion years, we think the
Sun is going to go through some changes.
Reactions inside the Sun will
change and cause it to swell up
and become a red giant star,
like Arcturus, which is orange.
At this scale, Barnard's Star doesn't even show up.
Arcturus is a giant star but it's not a supergiant.
Antares is a supergiant.
Arcturus is much smaller in comparison.
The Sun ... well maybe you
could see one pixel, maybe not,
and there's no hope for seeing Barnard's Star right now.
The supergiant star Antares is
in a group of stars called Scorpius.
At the beginning of summer,
Scorpius rises just as it's getting dark,
and it's up most of the night.
So next clear night, see if you
can find Antares, the red supergiant.
It will be between south and east, not very
high in the sky at the beginning of summer.
The other supergiant in this story is
Betelgeuse in the group of stars called Orion.
Now in Orion's story, he was a dangerous dude.
All the wild animals were scared of him
because he boasted he would hunt them all.
Well there was one animal, the
Scorpion, who thought he could deal with Orion.
In fact that's the story of Betelgeuse.
The Scorpion stung him in the shoulder right
there, and you can see the red mark he left behind.
Since they were both such epic characters
the Scorpion and Orion were put up in the sky —
that's what happens in these old stories.
But they weren't put up together
because they're rivals of each other.
So you never see Orion and
the Scorpion at the same time.
In fact if I were to point one finger at Betelgeuse,
and then pointed the opposite
direction, I'd be pointing down at the ground,
but if I could follow my gaze through the
Earth out the other side and toward the stars,
I would be looking toward Antares.
Well, roughly toward Antares, quite roughly actually.
But the Scorpion is up in the summer;
Orion's up in winter — they're opposite each other.
If you were pointing exactly opposite
Betelgeuse, you'd be pointing at this spot in the sky,
not too far from Antares, and this happens to
be the spot where the red dwarf Barnard's Star is.
So in the story of the two red supergiants:
They're both in the sky but you
never see them at the same time.
And there's an explanation for that.
We can look at the position of
the Earth in different kinds of year;
we can look at the position of the
stars of Orion and the stars of Scorpius.
Can you finish this explanation?
