How to Identify the Polestar and Its Importance in Astronomy
The Pole Star meaning is the North Star or Polaris that lies closely in line with the axis of the Earth's rotation "above" the North Pole, i.e., the north celestial pole.
The pole star or Polaris stands almost motionless or static in the sky, and all the stars of the northern sky surrounding this star appear to rotate around it. Therefore, it makes an excellent fixed point from which scientists draw measurements for celestial navigation and astrometry.
In this article, we will understand the polestar definition, how to find the pole star in detail.
Define Pole Star
The Pole star or polar star is the name of Polaris lies in the constellation of Ursa minor, as it is the star nearest to the earth’s celestial north pole that we can in the image below:
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So, basically, the Polaris is a multiple star system including Polaris A, a yellow supergiant in orbit with a smaller star Polaris Ab and they both lie in the orbit of Polaris B.
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Where is Pole Star Located?
When the earth rotates about its axis, the pole star ‘appears’ to remain stationary because the position of the earth remains unchanged with respect to the pole star. Pole stars are also known as Polaris or North Star.
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So no matter wherever we are residing on the earth and no matter what the time is, the position of the pole star remains on this axis. However, this is not the case with the other stars in the galaxy. Only, the pole star is visible from the northern hemisphere.
However, the Pole star will not last forever. For the last thousands of years, the earth’s axis has been rotating slightly. This is called ‘precession’ and this results in the pole star shifting from the axis. A time will come, the present pole star will vanish and some other star, which is lying on the axis of the earth at that time will become our new pole star.
Now, let’s understand how to find pole star:
How to Identify Pole Star?
To understand how to identify pole star or how to find pole star, we have a scenario to understand where the pole star is located.
Imagine a Blackball as Earth and the marked blue dot on the Ball represent the North Pole. Now, draw the Equator along with the circumference of the ball.
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Mark a black dot somewhere on the white wall that will represent the Pole Star.
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Now, hold the ball in your right hand in such a way that the blue dot on the blackball points directly towards the black dot on the wall. This pertains to the current position of how Earth and Pole stars are aligned in the universe.
Now, we will rotate the blue ball along with the North-pole (its marked axis).
We notice that the relative position of the dot on the wall, i.e., Pole star remains invariant with respect to the dot on the ball, i.e., North Pole.
Now, as we move a certain distance away from the blue dot on the Ball, i.e., the North Pole or head towards the Equator, still the relative position remains unchanged.
Fun Fact
Do you know that the distance between the Earth and the Pole star is 433 Light Years? So, in the actual situation, this relative position is difficult to signify. This is the sole reason why the pole star remains stationary in the sky.
Now, after crossing the Equator, what we do is, move towards the Southern Hemisphere, a straight line that joins the two points breaks directly.
At this moment, the pole star indicates the direction to the place where it becomes invisible. Therefore, it becomes difficult to say where the pole star is located.
What is Polaris?
Polaris is also known as the North star. It appears static in the sky because it is located near the line of the axis of the Earth that is projected into space.
It is only a bright star whose position relative to the rotating Earth remains unchanged, while all other stars appear to move in an opposite direction to that of Earth’s rotation under them.
At the North Pole, Polaris appears directly above with the other stars circling around it during the entire night. As we move south, i.e., away from the pole, Polaris appears further descended in the Northern sky but still remains at the center of daily stellar motions around it.
Below is the figure of the Polaris a.k.a the North star with other stars circling around it.
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Since there is no bright star in the South pole, the South Star exists in the universe. However, this is also true that the North star or the Polaris, or the Pole Star direction would always be towards the North because the Earth wobbles (moves unsteadily) like a top in its orbit.
Do You Know?
Polaris will eventually appear to move away from the pole and won’t be remaining a North Star after a period of 26,000 years.
FAQs on What Is Polestar in Physics?
1. What is the Pole Star and why is it also called the North Star?
The Pole Star, scientifically known as Polaris, is a star famous for its seemingly fixed position in the night sky. It is called the North Star because it is located almost directly above the Earth's North Pole. This unique alignment means that as the Earth rotates, the Pole Star appears to remain stationary, making it a reliable marker for finding the direction north.
2. How can someone locate the Pole Star in the night sky?
You can easily find the Pole Star using a well-known constellation, Ursa Major (also known as the Big Dipper or Saptarshi). Here are the steps:
- First, locate the Ursa Major constellation, which looks like a large kite or a question mark.
- Identify the two stars at the end of the 'bowl' of the Big Dipper. These are called the pointer stars.
- Imagine a straight line extending from these two pointer stars outwards from the bowl.
- Follow this imaginary line about five times the distance between the two pointer stars. You will find a moderately bright star along this line – this is the Pole Star.
3. What is the importance of the Pole Star in navigation?
The Pole Star has been historically crucial for navigation, especially for sailors and travellers in the Northern Hemisphere. Since it always indicates the true north, they could determine their direction at night without a compass. By knowing north, they could easily figure out south, east, and west. Even today, it serves as a reliable backup for modern navigation systems and is a fundamental concept taught in astronomy and survival skills.
4. Why does the Pole Star appear to be stationary while all other stars seem to move?
The apparent movement of stars is due to the Earth's rotation on its axis. Imagine a line extending from the Earth's North Pole out into space; this is the celestial axis. The Pole Star, Polaris, is located very close to this imaginary line. As the Earth spins, all other stars appear to circle around this point. Because the Pole Star is at the centre of this rotation, it appears fixed in its position from our perspective on Earth, acting as the pivot point for the entire night sky in the Northern Hemisphere.
5. Does the Southern Hemisphere have a Pole Star?
No, the Southern Hemisphere does not currently have a bright star that serves as a South Pole Star. While the Earth's southern axis of rotation also points to a specific spot in the sky (the South Celestial Pole), there is no prominent star located there. Navigators in the Southern Hemisphere use other constellations, like the Southern Cross (Crux), to approximate the location of the south.
6. How does the altitude of the Pole Star in the sky relate to an observer's location on Earth?
The angle of the Pole Star above the horizon, known as its altitude, is almost exactly equal to the observer's latitude in the Northern Hemisphere. For example:
- If you are at the North Pole (90° N latitude), the Pole Star will be directly overhead at a 90° angle.
- If you are at the equator (0° latitude), the Pole Star will be right on the horizon at a 0° angle.
- If you are at a city with a latitude of 30° N, the Pole Star will appear 30° above the horizon.
This principle is a fundamental concept used in celestial navigation to determine a ship's or person's latitude.
7. Will Polaris always be our Pole Star? Explain your answer.
No, Polaris will not always be our Pole Star. The Earth's axis has a slow 'wobble', similar to a spinning top, known as axial precession. This wobble causes the North Celestial Pole to trace a slow circle in the sky over a period of about 26,000 years. Because of this, the position of 'north' in the sky gradually shifts. In about 12,000 years, the star Vega will become the new North Star. Similarly, thousands of years ago, a star named Thuban was the Pole Star.
