Have you ever noticed that the stars sometimes appear brighter in December, January and February? There’s a link between cold air and the night lights.
“Part of it is that it tends to be drier in the winter,” said Diane Turnshek, an astronomer at Carnegie Mellon University in Pittsburgh, Pennsylvania.
Even though it’s invisible, moisture can change the way light moves through the air. And in the summer, all those water particles can create haziness that makes stars appear more dull.
On the flip side, everybody has experienced how dry the air can become in the wintertime. Think about how it sometimes feels like you can’t walk across a rug or touch a doorknob without generating static electricity.
“I pet my dog, and sparks fly,” said Turnshek, whose pooch is named Procyon after a star in the constellation Canis Minor.
Air temperature is also what puts the twinkle twinkle in the little stars.
“Even on very clear nights, some of the atmosphere is cooler, and some of the atmosphere is warmer,” said Turnshek, who also works with the Allegheny Observatory.
And when the light from a star passes through those bubbles of varying temperatures, “it bends and shifts the light, it refracts the light, so that we are seeing stars appear to dance or twinkle,” she said.
For stargazers in the United States, there’s another factor that comes into play for bright winter stars, although this is a matter of coincidence.
During Earth’s journey around the sun, “there are just simply more bright stars [visible] from the Northern Hemisphere in the winter sky,” Turnshek said.
Orion (pronounced Oh-ry-an) is one notable bright winter constellation. Named after a hunter in Greek mythology, Orion is best discovered by looking for the three sister stars (Alnitak, Alnilam and Mintaka) that are clustered closely together and make up a nearly straight line known as Orion’s Belt. The constellation also contains Betelgeuse and Rigel, two of the brightest stars in the winter sky.
“Most people can spot Orion even better than the Big Dipper,” Turnshek said.
But if you really want to see a shiny star, just follow the line created by Orion’s Belt down toward the horizon. There, you’ll see a fiery ball of gas called Sirius. At 8.6 light-years away, Sirius is relatively close to Earth and the brightest star visible in the night sky. It is also large — nearly twice as big as our sun and 20 times as bright.
So this winter, when the world turns cold and it seems like we should be spending more time indoors, consider asking an adult to go exploring outside. With a warm coat and a clear sky, any night can be turned into a treasure hunt. All you have to do is look up.