Star Brightness

  • star brightness is measured on a scale of magnitude that was first devised in 150 BC by the ancient Greek astronomer Hipparchus.

Ancient Greek astronomer Hipparchus
Born: 190BC, Nicaea, Kingdom of Bithynia (Turkey)
Died: 120 BC (around age 70) Rhodes, Roman Republic (Greek Island)

  • the brightest star that Hipparchus could see was Antares, and he described it as magnitude +1, he described the faintest star he could see as magnitude +6.
  • using telescopes and binoculars, astronomers can now see much fainter stars than Hipparchus could.
  • good binocular show magnitude 9+ stars, while a home telescope will show magnitude 10+ star.
  • brighter star than Antares have been identified with magnitude of less than 1+, and even minus numbers. Betelgeuse is 0.5+, Vega is +0.03, and the Sun is -26.7.
  • after the Sun, the brightest star visible from Earth is Sirius, the Dog Star, with magnitude of -1.46.

The brightest star visible from Earth is Sirius.

  • the magnitude scale only describes how bright a star looks from Earth compared to other stars – this is its relative magnitude.
  • the further away a star is, the dimmer it looks and the smaller its relative  magnitude is, regardless of how bright it really is.
  • a star’s absolute magnitude describes how bright a star actually is.
  • the star Deneb is 60,000 times brighter than the Sun. However, as it is about 1800 light years, it looks dimer than Sirius.

Size Comparison
Between Deneb star and our Sun.


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