Arcturus is the brightest star in the northern celestial hemisphere. It lies in the constellation “Bootes” and is known as “Alpha Bootes”. It is the fourth brightest star in the night sky, after Sirius, Canopus and Alpha Centauri. It lies barely 36.7 light-years from Earth, making it very close by celestial standards.
Early observations
Arcturus has been significant to observers since recorded antiquity. It was linked to the God Enlil and is also known as “Shudun”, meaning yoke, in ancient Mesopotamia. Ptolemy of ancient Greece described Arcturus as “subrufa” or slightly red. Prehistoric Polynesian navigators knew Arcturus as “Hōkūle’a”, the star of joy. This civilization used Arcturus as a navigational guide. The use of Arcturus is one of the methods by which Polynesians became such fabled sailors without any instruments.
Visibility
Arcturus can be observed during the day with a telescope. French mathematician and astronomer Jean-Baptiste Morin did this in 1635, making it the first star to be seen during the day. Arcturus is a type KO III red giant star. Visibly, it is at least 110 times brighter than Sun. However, most of the light given off by it is infrared and not visible to the naked eye. This is because the surface is cooler than the Sun.
Binary system
It is suggested that Arcturus is actually a part of a binary star system. The secondary star seems to be about 20 times dimmer than the primary one and orbits so close to Arcturus that it is not possible as of yet to distinguish it from the main star. There have been many focussed observations undertaken for this but the results remain inconclusive.
Arcturus became famous when its light was rumored to be the mechanism used to open the 1933 Chicago World’s Fair. The star was chosen as it was thought that light from Arcturus has started its journey at about the time of the previous Chicago World’s Fair in 1893. The star is 36.7 light-years from Earth and the light started its journey in 1896.
Compiled by: Madhurani Chavan