1) Polaris : a double star

The Polar star is a double star, it means it is related to another star by gravity. Polaris is in fact two stars which turn one around the other (binary). Its companion located at about 18,4 " (arc seconds) is much smaller and less luminous, its magnitude is about 9,10. The period of this rotation is 30 years. But on top of being a double star, it is a triple visual star, which means it is situated on the same line of sight as another star located much further away. If we look at it in a telescope, we can see 3 stars.

2) Polaris : a variable star

Polaris is a star that varies in luminosity (and thus in magnitude) according to a period of 3 days 23 hours 16 minutes 13 seconds. It' a variability of the Delta Cepheus type. The Polar star magnitude varies from 1,86 to 2,13.


from the online service of the VSNET

The measure definition is 0.1 magnitude, the curve is a simplified representation of Polaris variability.