Stars twinkle, while planets (usually) shine steadily. Why? Stars twinkle because Б theyБre so far away from Earth that, even through large telescopes, they appear only as pinpoints. And itБs easy for EarthБs atmosphere to disturb the pinpoint light of a star. As a starБs light pierces our atmosphere, each single stream of starlight is refracted Б caused to change direction, slightly Б by the various temperature and density layers in EarthБs atmosphere. You might think of it as the light traveling a zig-zag path to our eyes, instead of the straight path the light would travel if Earth didnБt have an atmosphere. Planets shine more steadily because Б theyБre closer to Earth and so appear not as pinpoints, but as tiny disks in our sky. YouБd could see planets as disks if you looked through a telescope, while stars would remain pinpoints. The light from these little disks is also refracted by EarthБs atmosphere, as it travels toward our eyes. But Б while the light from one edge of a planetБs disk might be forced to БzigБ one way Б light from the opposite edge of the disk might be БzaggingБ in an opposite way. The zigs and zags of light from a planetary disk cancel each other out, and thatБs why planets appear to shine steadily.
You might see planets twinkling if you spot them low in the sky. ThatБs because, in the direction of any horizon, youБre looking through more atmosphere than when you look overhead. If you could see stars and planets from outer space, both would shine steadily. ThereБd be no atmosphere to disturb the steady streaming of their light. Can you figure out which objects are stars and which are planets just by looking for the twinklers vs the non-twinklers? Experienced observers often can, but, at first, if you can recognize a planet in some other way, you might notice the steadiness of its light by contrasting it to a nearby star. Bottom line: Stars twinkle because they appear as tiny pinpoints as seen from Earth, even through telescopes. Planets donБt twinkle because they are closer, and thus appear larger in our sky, as tiny disks instead of pinpoints.
Though light pollution has made the night sky harder than ever to observe, a clear and dark evening can reveal to the eye roughly 2,500 twinkling stars, The Atlantic. В (There may be a septillion stars in the observable universe, but far fewer are visible to the naked human eye. )В There are few proofs as convincing as this в a sky crowded with flickering constellations в of the vastness of the universe.
But even the starsв signature twinkle signals something much greater. The closest star in the, beyond our own, is Proxima Centauri, a cool В from the sun. One of the farthest visible, the Andromeda galaxy, is more thanВ 14 quintillion miles away в that\’s a staggeringВ 14 million trillions. В Because it has traveled from such great a distance, the starlight that reaches Earthвs surface is little more than aВ spindly thread. But that light does notВ waver. Starlight shines straight and true. (That is, barring some long-ago celestial event only visible to us now. ) is a result of these thin but steady strands of light hitting the Earthвs atmosphere and bouncing around: reflected by airborne particles here, scattered by gas molecules there. Because starlightвs path is so narrow в having traveled from so far away в itвs easy to see these minor deviations. Planets, on the other hand, shine steadily in the night sky as seen from Earthвs surface. Thatвs because they are so much closer to us, and the light hasВ a much shorter distance to travel.
The light reflected off planets (whereas stars generate their own) has a much wider path than that of starlight. When you look at a planet through a telescope, you see a solid sphere. When you look at stars through a telescope, all you see areВ pinpricks. (Their light has traveled too far for telescopes to make much difference. ) And because theВ course of the light is broader, itвs harder to see how the light reflected off of planets is jostled around by Earthвs atmosphere. From space, stars shine and planets reflect without interruption, meaning twinkling night stars are a phenomenon best experienced from Earth в preferably from an, where light pollution has yet to cloud those beautiful, glittering skies. Stargazing hotspots and В are mostlyВ far-flung. Chile\’s Atacama Desert, for example, with itsВ high altitudes and dry, non-polar air, has become a booming destination for astro-tourism. Of course, there are more accessible options, including Cherry Springs State Park in Pennsylvania and (the 13,796-foot summit can be reached by car). В But there are few places on Earth where you can better experience the magic of thousands of twinkling little stars piercing the night sky. В