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 Tumshek, an astronomer at Carnegie Mellon University in Pittsburgh, Pennsylvania. Even though it's invisible, moisture (湿度) can change the way light moves through the air. And in the summer, moisture can make stars appear more dull.
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 Tumshek, 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, so that we are seeing stars appear to dance or twinkle," she said.
For star lovers in the United States, there's another factor that comes into play for bright winter stars, although this is a matter of coincidence (巧合). During Earth's journey around the sun, "there are just simply more bright stars visible from the Northern Hemisphere in the winter sky," Tumshek said. If you really want to see a shiny star, just try to find a burning ball of gas called Sirius near the horizon (地平线). 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.
