Brightest Stars

by Fraser Cain on January 28, 2009

Want to stay on top of all the space news? Follow @universetoday on Twitter

Red giant Betelgeuse. Image credit: Hubble Space Telescope

Red giant Betelgeuse. Image credit: Hubble Space Telescope


Have you ever wondered which are the brightest stars in the sky? That’s actually a complicated question because there are two ways to measure how bright a star is. One way is to define how bright the star looks from here on Earth; astronomers call this apparent magnitude, and it’s tricky because stars that look dim might actually be really bright, they’re just much further away. A more accurate way to measure the brightest stars is called absolute magnitude; this is how bright stars look from a common distance – 10 parsecs away.

Measured from here on Earth, the Sun’s apparent magnitude is -26.8; the brightest object in the sky by far. But if you measure the Sun’s absolute magnitude, it’s only 4.75. It would be just barely visible with the unaided eye.

So, the brightest star that we can see here on Earth is Sirius, which is best visible in the wintertime in the northern hemisphere. Astronomers measure the brightness of Sirius as -1.46 magnitude.

Here’s a list of the top 10 brightest stars in terms of apparent magnitude:

  1. Sirius (-1.46)
  2. Canopus (-0.72)
  3. Alpha Centauri (-0.27)
  4. Arcturus (-0.04)
  5. Vega (0.03)
  6. Capella (0.08)
  7. Rigel (0.12)
  8. Procyon (0.38)
  9. Achernar (0.46)
  10. Betelgeuse (0.50)

That’s a nice list of brightest stars, but remember, this list is apparent magnitude. These are the brightest stars that we can see from here on Earth. But if you measure all the brightest stars with an equivalent measuring stick: absolute magnitude; you get a much different list. And a bit of a problem. Even if a star extremely bright (luminous), but so far away that we can’t see it, then we don’t know it exists and so it can’t go on the list. The brightest stars are all supergiant stars with more than 50 times the mass of the Sun.

Astronomer Tim Thompson has compiled together a list of the brightest stars he could find. The brightest on the list is the Pistol star with an absolute magnitude of -14.2. Wikipedia has a similar list as well, with approximately 100 stars organized by brightness.

Were you wondering what’s the biggest star in the Universe?

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

References:
http://www.astro.cornell.edu/academics/courses/astro2201/mag_sun.htm
http://en.wikipedia.org/wiki/List_of_brightest_stars

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

Comments on this entry are closed.

Previous post:

Next post: