• Stars & Science Austin

The North & South Stars

Written by: Bobby Corley

Many people are not aware that the stars, like the Sun and the Moon, rise and set each night as the Earth rotates. Is there is a star in the night sky that does not seem to move? Yes! There are two of them. Astronomers with basic telescopes do not have to adjust their scopes to follow these 2 stars because they will not move out of their field of view. Navigators and Sailors all around the world rely on these two objects. These objects are basically known as the North and South Stars of the Nighttime sky.

These two stars seem to hover over the North and South Poles of our Earth. If you were living on the North Pole, the North Star would be directly overhead.

The same goes with the South Star if you were at the South Pole. Based on where one lives depends on how high the North or South Star is overhead. The North Star can be seen anywhere from 0° latitude to 90° North. The South Star can be seen from 0° latitude to 90° South. The angle of the North or South Star above the northern or southern horizon is equivalent to the latitude of the observer. So the North or South Star will tell you not only the direction of north or south, it will also tell you your latitude.

The North Star is found in the constellation of Ursa Minor, The Little Bear. The star’s name is Polaris. It represents the tail at the end of the Bear. The constellation is also known as the Little Dipper.

The light we see from Polaris is about 432 light years away.

One can use the two stars in the bowl of the Big Dipper to point directly to Polaris.

Many people think that, since it is of great importance to explorers, that Polaris is the brightest star in the Night Sky. It is not. It is only the 46th brightest!

The South Star is found in the constellation of Octans.

This is a very faint constellation that was devised by French astronomer Nicolas Louis de Lacaille in 1752, and it remains one of the 88 modern constellations.

The brightest star in the constellation is Nu Octantis, a 3rd Magnitude Star.

The star that is closest to the pole is Sigma Octantis. It goes by the name Polaris Australis.

This comes from the Latin word meaning, “South Star.”

The South Star is extremely dim, at magnitude 5.5. Despite this, it is closer to us than Polaris in Ursa Minor.

Polaris Australis is only 280 light years away. There is a way to find the South Star by relying on the smallest constellation that orbits the pole.

The constellation is Crux, the Southern Cross. Two of its stars, Acrux and Gacrux, represents the top and bottom of the Cross.

Use them and go four and a half times the distance between those two stars and then go about a degree and a half in the direction of the Southern Pole. There you can find Polaris Australis.

In addition to rotating, the Earth goes through a movement called Precession. This is the wobbling of the earth’s axis which causes both pole stars to change over many years. This motion is counterclockwise in the northern hemisphere and clockwise in the southern. A complete circle is done every 26, 000 years! It covers one degree of arc in the sky every 72 years.

The brightest North Star will be Vega in Lyra, The Harp, (in 14,000 AD). The brightest South Star will be Alsephina, in the constellation of Vela the Sails in 9,000 AD.

Just remember to look in the direction of North here in Austin and you’ll find a star that will not move in your lifetime!

If you enjoyed this blog post, share it with a friend!