Stars are like people. They’re good at hiding their personal side unless you get to know them well. Take the three stars of the Summer Triangle — Vega, Deneb and Altair. They’re bright, white-colored stars that shine the same way the sun does. Deep in their blazingly hot cores, hydrogen atoms combine to create helium, releasing energy in the process. That energy streams its way toward us as starlight.
Astronomers use everything at their disposal, from large telescopes, powerful CCD cameras, spectrographs (for studying the telltale presence of elements and molecules in a star’s light) and computer modeling to get to know the stars more personally. What emerges from their studies is a well-rounded, more three dimensional picture of all those twinkling points of light over our heads.
Let’s look at the Summer Triangle again and come to know its three main characters better. The chart above shows the sky around 9:45 p.m. in mid-August. You can use Jupiter, the brightest object in the night sky, to point you up to the Triangle.
The star Altair as compared to the sun. Altair’s rapid rotation causes it to bulge out at its equator. Photo: CHARA array, Univ. of Michigan, Ming Zhao and John Monnier
We’ll begin with Altair, the bottom apex of the triangle. Of the three, this is the only one we have an actual photo of. It was taken by the CHARA array, a group of six, high resolution telescopes on California’s Mt. Wilson. Altair is 17 light years distant and one of the closest stars visible to the naked eye. It’s about twice the diameter of the sun and spins so fast it completes one rotation on its axis in just 6 1/2 hours. Compare that to the sun, which takes 25 days to do the same. So let’s say you spot Altair at 9:30 at night. That means that by dawn the next morning, it will have made one complete turn. Wow!
Egg-shaped Vega is almost three times the size of the sun. This is an equatorial view of the star. In real life, we see Vega pole on. Illustration: RJ Hall
Next up is Vega, the brightest of the the three. It’s a mad, spinning demon too, completing one turn in 12 1/2 hours. Like Altair, its speed gives it a beer-belly equator. Vega is bright not only because it’s close to us — 25 light years — but it’s a hotter star than the sun and gives off 37 times as much light. Vega is surrounded by a disk of dusty, rocky material which astronomers believe is a solar system in the making.
Deneb (bottom half of frame) is 200 times bigger than the sun. If placed in the sun’s position in the solar system, Deneb’s incandescent surface would reach all the way to Earth.
The least conspicuous of our trio is Deneb, the top star of the Northern Cross. Behind its meek exterior however lies a white supergiant star 200 times the size of the sun. Deneb is one of the most brilliant stars of its kind in the entire Milky Way galaxy. If placed at Vega’s distance, it would be as bright as the fat crescent moon and cast shadows at night.
All this greatness is diminished by one thing — distance. Deneb is over 2600 light years away. That’s an incredible distance to see a star so brightly with the naked eye, and a testament to Deneb’s true nature. Deneb is so large that it will likely become a supernova sometime in the next million years, give or take. When that happens, it will finally have its due, outshining every star in the sky.