Brightest Star in the Night Sky

When you glance up at the stars at this time of the year, what is the first object you find in the sky? Well, with Jupiter super bright and rising at about 7 PM, it might be the gas giant. But there is something else in the sky that rivals Jupiter for brightness - Sirius, the brightest star in the night sky! See image below to find Jupiter and Sirius, set for Peoria at 8 PM.

Jupiter and Sirius are both very bright and easy to spot. Click on the image to enlarge. Image Credit: Stellarium

To find Sirius, it is best to first find Orion. If you need help finding the great hunter, check out last week's post. Once you find Orion, follow the line of his belt down to the brightest star you can see, and you have found Sirius.

Sirius marks the head of Orion's faithful hunting dog, Canis Major. Once you find Sirius, look for a line of stars extending to the horizon that marks the dog's body. He is sitting on his haunches, and has a front leg and back leg sticking out to the right. See image below with constellation lines to help your imagination. 

Can you find Canis Major? He follows Orion obediently through the night sky. Image Credit: Stellarium

The name Sirius derives from the ancient Greek for "glowing" or "scorcher". The heliacal rising of Sirius (when the star is visible for a short time just before sunrise) marked the flooding of the Nile in Ancient Egypt, and the "dog days" of summer for the ancient Greeks. The star was an important navigational aid to Polynesian sailors, who sailed between the islands of the Pacific using the stars.

The main reason Sirius is so bright is that it is very close, as far as stars go. It is only 8.6 light years away, the closest star (besides the Sun, that we can see from Peoria). A light year is about 6 trillion miles, so the star is only 51.6 trillion miles away. In contrast, Rigel, the bright blue star in Orion's foot, is about 860 light years away - 100 times farther! There are a handful of visible stars in our sky that are up to 8,000 light years away. So, in stellar terms, 8.6 light years is very close. 

Sirius as imaged by the Hubble Space Telescope in 2005. Can you see its tiny companion? Sirius is orbited by a white dwarf, invisible to the unaided eye. Image Credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester)

Sirius is actually a binary star system. With a powerful telescope a tiny companion star can be seen, Sirius B. Sirius B is a white dwarf, the second ever discovered. White dwarfs are the stellar remnants of stars not massive enough to go supernova and become a neutron star or a black hole. After a sun-like star uses up most of its hydrogen, it will puff up to a red giant. After shedding its outer layers to form a nebula, its core will be left behind - a white dwarf. This is the eventual fate of our Sun. You can see the white dwarf in the above picture. It is about half as massive as our Sun, but packed into a volume about the size of Earth! The original star was about 5 times more massive than our Sun. Sirius B is actually much hotter than Sirius A, the star we see. Sirius B is about 45,000 F, while Sirius A is about 18,000 F. Because the gas in Sirius B is SO compressed, it is cartoonishly hot.

In this image, Sirius B is the brighter light! This is an X-Ray image from the Chandra X-Ray Observatory. While Sirius B is incredibly faint in visible light, it emits a huge amount of x-rays. Image Credit: NASA/SAO/CXC

Because Sirius is so bright, ancient stargazers tracked the star carefully, often ascribing powerful abilities to it. Greeks and Romans made sacrifices to the star to keep disease away. On the Greek isle of Ceos, coins from the 3rd century BCE were found that feature dogs or stars with emanating rays. Many cultures saw a dog in this part of the sky, including the ancient Greeks, Romans, Egyptians, Chinese, and the Blackfoot, Cherokee, Pawnee, and Inuit tribes of North America. Homer referenced Sirius in the Iliad, describing the approach of Achilles toward Troy: 

Sirius rises late in the dark, liquid sky
On summer nights, star of stars,
Orion's Dog they call it, brightest
Of all, but an evil portent, bringing heat
And fevers to suffering humanity.

Sirius still plays a role in popular culture. Many science fiction and fantasy stories reference the bright star, and a satellite radio service chose its name and logo after the star.

Next time you are out at night, look up! Try to find Jupiter and Sirius - it will be easy to spot the brightest objects in the sky. When you find Sirius, just imagine all the other people who have gazed at the star throughout the centuries. Once you learn to find it, it will be your constant winter companion. 

To learn more about constellations and stars, visit the Dome Planetarium at the Peoria Riverfront Museum. Find showtimes and descriptions here. Or join us for an adult astronomy drop-in class!