Most people in the northern hemisphere have heard of the North Star, but few understand why it is such a fixture in our night sky.
In this article, you’ll learn about circumpolar stars, the circumpolar zone, and how to find the North and South Stars.
What Are Circumpolar Stars?
Circumpolar stars are, quite simply, stars that never dip below the horizon.
(The horizon is the line that delineates where the sky meets the ground.)
In the Northern Hemisphere, circumpolar stars appear to rotate around the North Star or Polaris, while in the Southern Hemisphere they appear to rotate around the South Star or Sigma Octantis.
What Makes The North Star, Polaris, Special?
Polaris is unique among circumpolar stars in that it is actually two stars – a binary system consisting of a bright, main star and a much dimmer companion star.
Polaris is also relatively close to Earth, at a distance of only 430 light years.
As a result, it appears much brighter than most other stars in the sky.
What is a Binary System of Stars?
A binary star system consists of two stars that orbit each other.
Binary stars are relatively common – it is estimated that up to half of all stars are in binary systems.
Polaris is just one example of a binary star system.
How Do Circumpolar Stars Move?
Circumpolar stars appear to rotate around Polaris or the South Star due to the Earth’s rotation.
This apparent motion is an illusion, of course – the stars themselves are actually stationary.
But from our perspective on Earth, it appears as though they’re rotating around the North or South Pole.
Why Do Circumpolar Stars Never Set?
Circumpolar stars never set because they’re always above the horizon.
This is due to their position relative to Earth’s axis of rotation.
Stars that are closer to the North or South Pole appear to rotate around those points, while stars that are further away from the poles rise and set like all other stars.
What Are Some Famous Circumpolar Stars?
Some of the most famous circumpolar stars include Polaris, the North Star; Sirius, the brightest star in the sky; and Vega, the fifth brightest star.
These stars are all relatively close to Earth and appear very bright in our night sky.
Why Are There No Circumpolar Stars At The Equator?
There are no circumpolar stars at the equator because the Earth’s axis of rotation is not perpendicular to the plane of its orbit around the sun.
The Earth’s axis is tilted at an angle of about 23.5 degrees, which means that the North and South Poles are not directly aligned with the sun.
As a result, there are no stars that appear to rotate around the sun at the equator.
Can You See Any Circumpolar Stars From The Equator?
Yes, you can see some circumpolar stars from the equator, but they will not appear to rotate around the sun.
Instead, they will rise and set like all other stars.
The number of circumpolar stars that you can see from the equator will depend on your latitude – the further north or south you are, the more circumpolar stars you will be able to see.
Tips For How To Locate The North Star
The North Star, Polaris, is the brightest star in the constellation Ursa Minor (the Little Bear).
To find Polaris, look for the Big Dipper in the constellation Ursa Major (the Great Bear).
The two stars at the end of the Big Dipper’s “handle” point to Polaris.
Polaris is not as bright as some of the other stars in the sky, but it is very easy to find.
If you are struggling to find Polaris, you can use the simple constellation phone app like Star Walk 2.
This app will show you exactly where to look for Polaris, as well as all of the other stars in the sky (as well as planets).
Tips For How To Locate The South Star
The South Star, Sigma Octantis, is the brightest star in the constellation Octans.
To find Sigma Octantis, look for the Southern Cross in the sky.
The two stars at the end of the Southern Cross point to Sigma Octantis.
What is the Circumpolar Zone?
The circumpolar zone is the area of the sky around the North or South Pole where circumpolar stars can be seen.
This zone extends from the horizon to a point directly overhead.
The size of the circumpolar zone depends on your latitude – it is larger at higher latitudes and smaller at lower latitudes.
For example, the circumpolar zone is very large in Alaska but very small in Florida.
The circumpolar zone is also sometimes referred to as the “polar circle”.
This name is misleading, however, because the polar circle is actually a line on the globe that delineates the northernmost or southernmost point at which the sun can be seen on the winter solstice.
The polar circle is not related to the circumpolar zone.
Are There Any Other Circumpolar Constellations?
Yes, there are other circumpolar constellations. In addition to Ursa Minor and Octans, the constellations of Cepheus, Cassiopeia, and Cetus are also circumpolar.
These constellations are all located near the North Star (Polaris) and can be seen year-round in the Northern Hemisphere.
In the Southern Hemisphere, the constellations of Tucana, Hydrus, and Mensa are circumpolar.
These constellations are all located near the South Star (Sigma Octantis) and can be seen year-round from South of the equator.
Interested in learning more about constellations and stars? You might like:
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- Best Constellations Everyone Should Know