why do some stars appear to twinkle

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.
Why do stars twinkle? Though it wouldnвt work so well in the nursery rhyme, a there is actually a technical term for when stars twinkle:В astronomical scintillation, an effect due to our planetвs atmosphere. As light travels through the blanket of air around our planet, it is diffracted (bounced around) causing a quick apparent dimming and brightening в a star's signature "twinkle". While some stars do physically over time, they typically do so on long timescales в these changes sometimes over hours, but more often over days, weeks, or years. These variable stars are well studied and often signal complex physical changes happening to the stars in question. The more rapid changes of scintillation, on the other hand, come about long after the light has left the star. Light waves traveling through Earthвs atmosphere diffract as they pass through pockets of air at different temperatures.

Because the light waves come from a single point, this effect can make the starвs brightness and/or position appear to change. Why Don't Planets Twinkle Too? Unlike stars, planets don't twinkle. Stars are so distant that they appear as pinpoints of light in the night sky, even when viewed through a telescope. Because all the light is coming from a single point, its path is highly susceptible to atmospheric interference (i. e. their light is easilyВ diffracted). The much closer planets appear instead as tiny disks in the sky (a distinction more easily discerned with a telescope than with the naked eye). Their apparent sizes are usually larger than the pockets of air that would distort their light, so the diffractions cancel out and the effects of astronomical scintillation are negligible. will help you find your way among the twinkling constellations, and you can trace the appearance of the planets along the ecliptic with a.

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