Night comes early this time of year, and on clear evenings at Crossroads at Big Creek, we have had spectacular views of the night sky…..the planet Jupiter surrounded by thousands of twinkling stars. And as they leave our evening programs, people often ask why stars twinkle?
Twinkling has to do with distance and the way our eyes work more than anything else. Many of the stars we see in the night sky are gigantic beyond our imagining, but because they are so very very far away from us, they look just like tiny points of light. Even through a telescope, stars look like pinpricks. My heart and mind know stars are huge, but my eyes see them as tiny. Your eyes do too.
Look at a planet through binoculars or a telescope (and you’ll have that opportunity this weekend) it will appear to be a round disk. You might even see moons. Planets appear much larger than stars, even to the naked eye. But we are absolutely sure that they are smaller. Smaller, but closer. And the moon? It’s really small (by space standards) but it’s also closer than anything else, so to our eyes, the moon looks huge, especially when it is near the horizon.
So what makes an object seem big is not necessarily its size, but distance. And the celestial objects that our eyes see as “big” tend not to twinkle while the things that seem to be tiny pinpricks of light do.
Here’s the deal. Light travels from the stars to us. It may take a few years or hundreds or even thousands of years for the light to reach to us, but just before the ray of light reaches our eyes, it has to pass through several layers of air.
When the light of a star passes through the layers of atmosphere, the air acts like a lens and bends the light ever so slightly in some random direction. The next layer also bends the light in a slightly different direction. The more layers of air, and the more turbulent the layers, the more times the light ray is bent. When it reaches our eyes, the light seems to jiggle slightly…to twinkle.
Remember, we know that the planets are smaller than stars, but they are much, much closer. Consequently, to our eyes, they appear larger. When we look at a planet, many light rays reach our eyes. The different rays may be bent in slightly different directions and some of those light rays might be brighter than others. But when the receptors in our eyes gather these rays and send information to our brains, our brains somehow average all of the rays into one steady image.
Planets, then, seem not to twinkle. At least they seem not to twinkle unless they are very low in the sky. Then, the light has to travel through so much atmosphere, especially when there is a great deal of turbulence, that the rays are bent much like light passing through a prism. When this happen, planets might twinkle just like a little star. And the more we on Earth learn, the more we “wonder what they are.”
For those who want to experience star or planet-gazing, the Door Peninsula Astronomical Society is offering a Viewing Night on Saturday, February 18 at the Astronomy Campus at Crossroads. Beginning at 7:00 PM, members of DPAS will be in the StarGarden with telescopes and astronomical binoculars available for visitors. The planet Jupiter and several of its moons will probably by the highlights of the evening, but one never knows. This will be a clear-sky only event. To reach the Astronomy Campus, turn east on Utah Street and travel up the hill. At the stopsign, turn left into the Crossroads preserve. Night vision-friendly red lights will show you where to go.
