The North Star (Polaris)
The North Star, also called Polaris, is of famous for the fact that it indicates the north. The best way to find it is to search through the saucepan from the Big Dipper and to draw a line upwards from the two outer stars of the pan (Merak and Dubhe). It is the next bright star. A common misunderstanding is that the North Star is the brightest star in the sky. That it can not deliver in the slightest. But recent research indicates that the North Star is rapidly changing, and it might be rising in this list.
Facts and figures about Polaris
- Constellation: Ursa Minor
- Scientific name: Alpha Ursae Minoris
- Position: right ascension 02h31m49s.09, declination + 89d15m50s.79
- Class: F7Ib-II (white-yellow, borderline between giant and supergiant)
- Magnitude: around 2.0 (slightly variable – Cepheid)
- Mass: 6 times the sun
- Distance: 433 light years
Many owe a lot to the Northern Star. Explorers who crossed the oceans knew exactly which direction to go, and many adventurers lost in the wilderness could find their way back to civilization with the North Star’s guidance. The North Star has not always been the lodestar and it will not remain. During Roman times Kochab (Beta Ursae Minoris) was closest to the north celestial pole. Before, it was known as Thuban in the constellation of Draco. In the future Polaris will be surrounded by a number of stars in the constellation Cepheus. Then, by Deneb and in about 12,000 years; Wega. The Celestial Pole’s movement is caused by the spinning motion of Earth which lasts for around 26,000 years. The precession is also the process which ensures that the constellations such as Zodiac, change over the centuries.
The North Star is a whitish yellow star with the magnitued of 2500 once the Sun is between a ‘normal’ giant star and a supergiant. Its diameter is 45 times that of the Sun and for a heavier giant this indicates that it is in a transition phase. The fact that the brightness pulses and varies. (so that it can not be seen with the naked eye) is an additional indicator. Analysis of previous documentation shows that the star’s brightness has increased by 15% in the past century and it’s had a full magnitude of about 250% since the Ptolemy’s time (90-168)! However, the variation in brightness has decreased since the 1990’s and the periods have become longer. What this means for the future of the North Star is unclear.
The co-guardians of the Pool
Like many stars, the North Star is not alone. Polaris B is 360 billion kilometers from star A. It’s magnitude is 8.2 with an arc distance of 18 seconds. With a medium-sized telescope these can be see separately. This star is slightly large hotter, and 1.4 times heavier than the Sun. The same applies to type F7V with a mass that is 1.2 times larger the Sun or Polaris Ab. This is less than 3 billion miles from star A and it was seen for the first time in 2006. It was discovered using spectroscopy by measuring and analyzing anomalies in the light of star A. Both stars burn hydrogen in their cores and take a lot of time to follow after their parent star. They are about 70 million years old. There is also a Polaris C and D; both very faint stars with magnitude’s of 12 and 13. Although all three are bonded, there is little known about these two. If the assumptions are correct, they may even be red dwarfs. (Small stars that can live for up to thousands of billions of years.)
The North Star as Cepheid
As previously mentioned, the Pole Star’s brightness can vary. However, it probably shouldn’t be grouped with the Cepheid, a group of stars that help determine distances in the universe by using the frequency of their brightness pulsations. The North Star is the brightest and closest star to Cepheid. This gives researchers the opportunity to understand these stars and where the regular pulses come from. In it’s last phase the North Star it will most likely be worn down to a more “average” Cepheid. It is too large and light to explode as a supernova so, (even with a place on the list of brightest stars) after its time as a bright red giant, the outer layers will be repelled and it will end up as a heavy white dwarf.