Contrary to popular belief, the brightest star in the sky is not the North Star. In fact, the brightest nighttime star is Sirius, a binary star system made up of one extremely bright star called Sirius A and a fainter star called Sirius B. Some people also consider the Sun to be the brightest star in the sky, but it usually is discounted because it shines during the day and at night. The second-brightest nighttime star is Canopus, which is less than half as bright as Sirius. The North Star, also called Polaris, is the 45th-brightest star.
More facts about stars:
- It's difficult to definitively say which star is the brightest, because there are different ways to measure the brightness: apparent magnitude and absolute magnitude. Apparent magnitude is how bright stars appear when viewed from Earth, and absolute magnitude is how bright stars are in general. When considered in terms of absolute magnitude, the brightest star is thought to be R136a1.
- The system for categorizing stars dates to about 150 BC. A Greek astronomer named Hipparchus made an apparent magnitude scale that ranged from 1 to 6, with the brightest stars being in category 1.
- The brightest star in terms of apparent magnitude isn't constant — it actually changes as stars orbit throughout the galaxy. There have been 10 brightest stars, counting Sirius, in the past 4.5 million years or so. Canopus, the second-brightest star in the sky as of 2011, has been the brightest star three times.