Welcome! In this video we will discuss Polaris, one of the most important stars
to know in the sky. If we take a look at this picture, this photo is a star trail
picture and it is a long exposure photograph that allows us to capture the
apparent motion of the stars in the sky. Now in reality the stars only appear to
move in the sky because of the Earth's rotation and as you look at this picture
I want you to notice the single dot that stands out from the rest of the star
trails. This star is known as Polaris and this is a star that appears to not move
in the sky and this is important especially in terms of navigation
purposes. The North Star has had very many names over the course of time
including Polaris, The Pole Star, The Loadstar, Stella Maris.
Each name is different upon how the culture viewed this star and it's
located in the constellation called Ursa Minor, which is also known as a little
bear in terms of modern astronomy, and if you look at this picture Polaris is the
brightest star out of all the other ones in this constellation. Here is Polaris
okay and then as you follow down the handle you have the dipper part of the
Little Dipper and these two stars have been called the guardians of the pool
because as they go around the North Star they guard the pole. One misconception about
the North Star is that many people think that it's the brightest star in the
night sky but this is not true. Actually it's only about the 49th brightest star
in the sky. Sirius, the bright star in Canis Major which is found in the winter
sky, really is the brightest star in the night sky. If we wanted to find Polaris
the best way to do that is to find the Big Dipper within the very large
constellation of Ursa Major. What you would do is then use the pointer stars
so here the pointer stars and this is the Big Dipper which is really a part of
Ursa Major which is a larger constellation and it doesn't even fit in
this entire picture but you find the pointer stars and it will point you
right to Polaris. From there you can find the Little Dipper. Just as an aside
notice how the handles of the dippers are different this one curves in one
direction this one curves in another and the brightness is a little bit different
too. The Big Dipper all the stars are relatively the same brightness, where in
the Little Dipper you only really have three bright stars out of the seven that
are there and what's interesting is that Polaris can be used to determine your
latitude in the northern hemisphere. If you take a look at this picture you can
see that if you can measure the degrees in which Polaris sits off the horizon
this will give you your latitude in degrees in the northern hemisphere. Let's
get some more practice with trying to identify Polaris and how to find it. So
as you look at this picture see if you can find the Big Dipper. Always
remembering that the Big Dipper is really just a smaller part of the
constellation called Ursa Major. So if you can find the Big Dipper which is one
of the most famous asterisms out there or patterns within a pattern you should
be able to find the pointer stars and the cup portion of the Dipper and then
let it lead you right to Polaris. Now if I were to trace
this out for you in order to help you out
notice the Big Dipper right here here's the handle here's the cut portion okay
and then the pointer stars are right here what you want to do is use a
pointer stars to point you to Polaris and then finally to visualize where Ursa
Minor is. We've got Polaris up here the brightest star we go down you connect it
right here like this just remembering that in Ursa Minor there's only three
bright stars the rest are very faint to see so when you actually go out you may
only see the three stars of Ursa Minor while compared to the Big Dipper
all the stars are relatively the same magnitude. Remember use this trick every
time to help you find where Polaris is and go outside and keep practicing how
to find it. If we zoom in on Polaris using a high-powered telescope we would
find that it has a system of more than one star. Polaris A is a yellow
supergiant which means it's a star that's coming towards the end of its
life and this supergiant star has a companion star that's called Polaris AB
and these two stars revolve around each other every 29 years or so and this
discovery of the smaller this smaller star right here was made by the Hubble
Space Telescope in 2006. The other star in this system is called Polaris B and
it is pretty easy to find with a telescope. William Herschel in 1780
observed this star with a fairly modest telescope but at the time it was
considered one the best telescopes out there and this star is classified as a
main-sequence yellow star and it has a mass of about 1.3 Suns.
Polaris A on the other hand is much bigger like I said it's a yellow
supergiant, a star that's starting to expand and fuse its hydrogen and the
outer cores, and this star is estimated to have the mass of 4.5 suns and if we
compare Polaris AB this again is much much smaller about the mass of 1.2 sons.
So very much similar to Polaris B. This entire system is estimated to be 433
light years away. So why does a North Star appear stationary? Before we look at
why Polaris appears to not move in the sky it is important to understand the
orientation of the earth. The Earth's rotational axis is tilted about 23 and
1/2 degrees and this tilt is one of the reasons we experience his seasons at
certain times of the year the sun's light will shine more directly on
certain parts of the earth which causes the summer months. During the winter the
sun's light is spread over a larger area and this makes that area much cooler
causing winter. To get back to Polaris the position of this star pretty much
sits right over Earth's rotational axis therefore this star appears not to move
and sometimes we call this a North celestial Pole but Polaris will not
always appear to remain stationary in our sky. In order to understand why the
North Star will not always remain the star above the North celestial pole we
have to look at a phenomenon called precession of the equinoxes. Over the
course of 26,000 years the Earth's axis wobbles like a gyroscope. The ancient
Greek astronomer parkus first notes this when he noticed that his measurements of
the Stars were slightly different than the very ancient
Babylonian measurements. He concluded that the precession is a reason for this
change and this phenomenon is called by caused by the gravitational source of
the Sun and Moon in addition to the fact that the earth is actually a spheroid
and not a perfect sphere. So since the earth is tilted the Sun's gravitational
pull is stronger to the portion that is tilted towards the Sun which creates
this torquing effect on the planet. If the earth were a perfect sphere there
would be no precession. So this also means that Polaris will not always
remain above the North celestial Pole and if we look at the motion of a
gyroscope, this is what the earth does within its orbit over the course of
26,000 years, if we look at this diagram it illustrates the path of the North
celestial pole over the course of 26,000 years. Right here is Polaris and this is
where the North celestial pole points today but 4,000 years ago during the
time of the Egyptians the North celestial pole was aimed at a star
called Thubin and this is located in the tail of Draco the dragon, and if we fast
forward 12,000 years from now the bright star Vega in the constellation Lyra will
lie very close to the path of the North celestial Pole. Well we have come to the
end of our video about Polaris which is also known as the North Star. So I want
to take a moment to just review over everything that we covered in this video
the importance of Polaris is that it is a star that never moves in the sky or it
appears to not move. Since it is stationary this is a very important star
in terms of navigation it helps you find the direction of North. In order to find
it you need to use the pointer stars of the Big Dipper and it will lead you
straight to Polaris and from there you can find the rest of the Little Dipper
so again the big within the constellation Ursa Major
find the pointer stars and it'll lead you right where you need to go. If we
take a look at this star system and zoom up a little closer with a very
high-powered telescope this is a three star system we have Polaris A which is
the largest star it's four and a half times the mass of the Sun and then you
have Polaris AB which is another small star that's orbiting Polaris A and then
you also have Polaris B. Polaris AB and Polaris B are much like the Sun there
are just a little bit times more massive than the Sun but not by much and this
system is 433 light-years away. One cool thing to remember is that Polaris will
not always remain over the North celestial Pole due to the gyration of
Earth's axis ,which we also call the precession of the equinoxes. If you have
any questions please leave your questions in the comments below and I
will definitely be sure to answer you thank you so much for watching and good
luck finding the North Star