Scale of distance to closest stars | Scale of the universe | Cosmology & Astronomy | Khan Academy

Before we start going
off into things outside of our solar system, I want
to take a few steps back because I found this neat
picture of the Sun over here. And the reason why,
at least in my mind, it’s kind of mind blowing
is because at this scale, the Sun is obviously still
a huge object at this scale. The Earth would be
roughly– and this is an approximation–
roughly that big. And so for me at least,
this is mind blowing. Because it’s this idea
that our whole planet, everything could fit into one
of these kind of plasma flares coming off of the Sun. And you can only imagine it. We can’t realistically be there. But if you were in some
type of protected capsule, what it would be like to be in
this type of an environment. So I just thought this was
kind of a fascinating concept. Well, anyway, with
that out of the way, let’s think about
what it means to be at the boundary of
the solar system. In the last video, we
explored the Ort Belt. It started a little under one
light year away from the Sun. But depending on what
you view as the boundary of the solar system, it could
be something way farther in or could be something as far
out of something like the Oort Cloud. So the Sun, we see these
things being ejected. But even in unseen ways,
or unseen particles, super high energy electrons,
electrons and protons, are also being
ejected from the Sun at super high velocities,
400 kilometers per second. Let me write that down,
400 kilometers per second. And on Earth, we’re protected
from these highly energetic particles because of
Earth’s magnetic field. But if you’re on the
surface of the Moon when the Sun is on
top, and you’re not on the dark side
of the Moon, you’ll have direct contact with these. And as you can imagine,
it’s not the best thing to hang around in too along. But the whole reason why I’m
even talking about these, these charged particles that are
coming out at huge velocities from the surface
of the Sun, these are considered the solar wind. These are the solar wind. And I’ll put “wind’ in quotes. Because it’s really
very different than our traditional
association of a nice breeze. These are just
charged particles that are going out at super high
velocities from the Sun. And I’m even going into
the idea of the solar wind because to some degree,
they can help us with one definition of maybe
the limits of the solar system. And that’s the limits of how
far the solar wind is getting before it kind of
comes in confrontation with the interstellar medium. And this right here shows
a depiction of that. So the Ort Cloud, it
was way– at least the edges of the dense part
of it is way outside of this. As we saw, this is just
where Voyager 1, Voyager 2. If we wanted the orbit
of Sedna, the close part would be something over here
and then it would go out. But the Ort Cloud is
much, much further out. So if you look at this kind
of view of the solar system as the extent of the solar wind,
its much smaller than the Ort Cloud. But it’s still fairly large. So this is right here. This heliopause right here–
and I got this from Wikipedia– this is essentially where
the velocity and the forces of the solar wind
are counteracted. That the pressure is so
diluted at this point that it’s counteracted by mainly
the hydrogen and the helium that’s in the interstellar
kind of medium, that’s just kind of out there. So after this point,
it’s not really being injected out anymore. There’s this kind of pause,
I guess you could say. And Voyager 1 and
Voyager 2, as I said, have essentially gotten pretty
close to, people believe, that pause over there. And so that’s one view of the
edges of the solar system. There’s never going to
be any hard edge to it. Another view would be something
like the Oort Cloud, the area where you have the
still objects out there. And actually we haven’t
directly observed objects in the Ort Cloud. We think that they
are out there. And then maybe the most
abstract definition would be a significant
influence from the Sun’s gravitational pull. So all of those
ways are to imagine the extent of the solar system. But they all kind of leave a
grey area for what is and what is not in the solar system. But my whole point
here, what I want to do is start exploring a little
bit outside of the solar system and just give you a
sense of the scale as we just go to
the closest star. So if we go right
over here, this shows our local neighborhood
from a stellar point of view. And even though these stars
look pretty big, if you actually were to draw– this is our
solar system right here. And you might be saying,
oh, maybe that’s the Sun. No. The Sun, if you were
to draw it here, it wouldn’t even
make up one pixel. In fact, the entire orbit of
Pluto, everything inside of it, still would not make up one
pixel on the screen right here. What we see right here,
which is a radius– it’s roughly a radius of about
give or take a light year– this is roughly maybe the
radius of the Oort Cloud. And we saw in the
last video, how huge that was, especially
relative to the radius of say Pluto’s orbit, which
is roughly like that. And that itself is a huge, huge
diameter or a huge distance away from the Sun. And that wouldn’t
even make a pixel. That wouldn’t even make
a pixel on this diagram right over here. But just to give you an
idea of how far we are– so we’re a speck of a speck
of a speck inside here, of a pixel of a
pixel in the center here– to make it
from our solar system, or in particular
from Earth maybe, to the nearest star or
maybe the nearest cluster of stars, the Alpha Centauri. They’re the nearest
cluster of stars. There’s three stars,
Alpha Centauri A, which is the largest;
Alpha Centauri B; and then, there’s one
that you can’t observe with the naked eye,
Alpha Proximus. Or I think it’s
Proximus Centauri, I think is what it’s called,
not Alpha Proximus, Proximus Centauri. But that’s a much smaller star. But that’s the
closest star– well, you could view it as this whole
cluster of stars right here. And they’re the closest– is
about 4.2 light years away. Or another way to
think about it, if someone were to shine a
light on one of these planets, and assuming that
light could get to us, it would take 4.2
years to get to us. Or if these guys just
disappeared or blew up, we wouldn’t know
it for 4.2 years. And you might say, hey,
that’s not too bad. We should take a trip over
there and check them out, see if there are any
other people there that we can meet and exchange
technologies with, or whatnot. But this is a huge distance. Just this 4.2 light years is
an unbelievably ridiculous distance. And just to give you a
sense, the Voyager 1 and 2, we talked about
in the last video, and we can even see
how far they’ve gotten. They’ve gotten to pretty
much to the heliopause. These guys are traveling at
60,000 kilometers an hour, which is the same thing as
17 kilometers per second. If we were able to get up
to those type of velocities, and these guys got up to
those type of velocities by leveraging the gravitational
pull of some of the larger planets to accelerate
and keep accelerating. So this is a pretty hard
velocity to actually reach. But if you were able
to reach that velocity and go straight in the direction
of the direction of the Alpha Centauri system, the
closest stars to Earth, it would take you
80,000 years traveling at the same velocity
as Voyager 1, which is the fastest
of the Voyagers. So it’s a ridiculously
long time. So we’re going to figure out
some better way to do that.

  • It is incredible. It's always bothered me that science fiction imagines densely-packed star systems or thick asteroid belts. In reality, even if you were in the middle of the thickest part of the asteroid belt, you'd be lucky to see a single rock. The distances are that huge.

  • What's interesting about Alpha Centauri A is that, except from being part of a multiple star system, it's very similar to our sun. A hypothetical earth would have to orbit at a distance between our own earth and mars to receive the same amount of brightness.

    It would be very exiting if we ever discover a planetary system there.

  • 80k years isn't acurate, voyageur wasn't designed for speed, it's basically drift wood.
    2k years is far closer to what is viable for a interstellar mission.
    Might be forever in terms low grade sci fi, but it terms of civilization i.e. the romans egyptians etc, it's just the next step. In terms of human evolution it's just a blink.

  • If you travel at Voyager I's speed to the closest Earthling-livable planet which is roughly 20 light years away, even at 11mp second it'll take 350,000 years!!!

  • @Stevesrssrssrs Yea. Its actually pretty impossible for us to get anywhere interesting in the universe, or for anyone to get to us, unless we or them manage to travel at close to the speed of light, or above, which as we now know, is possible…probably… 😛

  • I think that man is going about space travel the wrong way. Instead of traveling by spaceships and warp drives. We have a mind that is only used at a 10% level on the smartest levels. If we had the mentle ability of say 50-70%. Man may be able to travel above light speed by out of body travel. I know it sounds weird. But n this way we are not subject to the negative effects of space and time.

  • To travel anywhere n the known universe without ever leaving earth. We do it all the time n sifi movies. Like looking at a picture and then being in that picture.

  • 80 000 years to get to alpha centauri onboard voyager1!!! wow!!! so if there is no life at the moment, that can evolve during that 80 000 years and during this time we can die!!! only voyager will do the job and give some information about us. that is so scary. we are lonely and still dont have respect to our planet. people start to think about that what we do to save our world its already 7bilion of us!!!!

  • yep, proxima centauri has an apparant magnitude of 11,5 while we can only see till magnitude 6 with the naked eye.

  • Any information on what the estimated distances are for other solar systems to each other (not including ours) really curious. I'm sure there's solar systems closer to each other than 4.2LY

  • Hey there, I know this video is a few years old but I am just wondering why we cannot just "zoom in" on one of the billion earth like planets in our galaxy or in others near by to see if there is any other life forms out there? I mean if the Hubble telescope can zoom way out to see galaxies that are 13 billion light years away why can't we do this for something that is within 1000 light years away? It may be a stupid question with an obvious answer but thank you to anyone who knows the answer and can help me out!

  • The sheer distances to the planets is one thing, and that is mind blowing. The distances to other stars in our stellar neighborhood is another thing, and that too is mind blowing. The distances across galaxies is yet another thing, and THAT too, is utterly mind blowing. The distances between galaxies is yet ANOTHER thing and that, again, is totally mind blowing. The distances between and to these things in our Universe has, and always will, boggle the, and my, mind. My brain runs out of gas trying to comprehend the distance here on Earth and the moon, let alone from here to Mars or Jupiter. Completely staggering to think about, that's for sure. Whenever you start to think you're some hot shit here on planet Earth, first, consider the size of the Earth. Then, consider the size of the Solar System. Then, consider the size of the stellar neighborhood. THEN, consider the size of the galaxy….catch my drift? We are basically nothing and something at the same exact time

  • 🙂 is it me or is sal stumbling over his words very frequently during this video series ? its like trying to comprehend the distances and scales it detracting frm his ability to formulate a sentence, or maybe hes just overwhelmed by a childish joy – either way i love this channel and the idea of khan academy, its givn me a seconds chance at life.
    also NO MANS SKY ! the excitement is real !!!

  • I love learning from you Sal, even though I have never met you I feel like you're some kind of an older brother that I wish I had, especially since I grew up with no one to look up to and having almost no friends, it feels like you're someone I can always run to and ask questions knowing that you will have answers. Anyway don't mean to sound like a weirdo but yeah its true I wish i could meet you in person haha thanks for all these vids.

  • according to their distance from Earth, which is the nearest first and the farthest last…… stars, cloud, moon or the sun??????

  • If you use Linux I wrote a Python script that does these calculations; it is very revealing! :
    At the bottom of this page:


  • how is it, to the naked eye, all the stars look somewhat equal distance from earth? if the distances between and away from earth are so vast why does it appear that they are equal size and distance

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