What Makes Stars Twinkle?

On a clear night, the stars seem to wink and twinkle in the sky. Learn why in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff from how stuff works, Hey, brain
stuff luring vocal bomb here. All things considered, our atmosphere
is pretty great. This blanket of nitrogen, oxygen, and other
gases keeps the world's temperature nice and habitable while protecting
us from harmful UV radiation. To say nothing of this
space debris vaporizes for us. Oh yeah, and without all

(00:24):
that oxygen in our atmosphere, animal life couldn't survive on
planet Earth. Not a bad resume. But despite its many
good qualities, the atmosphere can be a nuisance to astronomy buffs.
That's because it distorts light. At night, the atmosphere makes
some heavenly bodies appeared to flicker and shimmer. The technical
term for this phenomenon is astronomical scintillation. You probably know

(00:48):
it by a different name, twinkling like an onion. The
atmosphere is made up of layers. At the bottom is
the troposphere, which starts right here at ground level on
the planet's surface. Standing about five to nine miles that's
eight to four point five kilometers tall, It's where most
of Earth's weather events take place. The other layers are
in ascending order, The stratosphere mesosphere, thermosphere, and exosphere. There's

(01:13):
also a region called the ionosphere, which encompasses parts of
both the mesosphere and the thermosphere. These layers have different temperatures.
In addition, the air's density varies from level to level.
When starlight enters our atmosphere, it runs into pockets of
cool and warm air. The pockets act as big lenses,
causing the light to change direction or refract as it

(01:36):
passes through them. Yet the lenses are not fixed in place.
They move around and change shape as they shift. So
does starlight refraction. That's why the stars appear to twinkle.
Scintillation affects planets to Mercury, Venus, Mars, and the other
planets in our Solar system do twinkle when viewed from
Earth on a clear night. So does our moon. However,

(01:59):
the planets twinkled to a barely noticeable degree distance is
the main reason stars twinkle more conspicuously than the planets
in our Solar system, because the former are so far away,
each star looks like a single pinpoint of light, a
single pixel. You might say. It's a different story for
Earth's moon and our neighboring planets, being a lot closer

(02:21):
they're less affected by the atmosphere. Planets and moons appear
as tiny disks up in the sky. The light they
emanate comes not from a single point, but from many
individual points, all clustered together. These rarely scintillate in unison,
which is why planets and moons don't twinkle as dramatically
as the stars, So twinkling can only happen when an

(02:42):
atmosphere is present. It's for this reason that photos taken
by the Hubble telescope looks so clear. There aren't any
atmospheric air pockets to refract the starlight. Earth Bound astronomers
use telescopes with adaptive optics systems to compensate for twinkling,
making the stars look more stable. Today's episode was written

(03:04):
by Mark Mancini and produced by Tyler Clang. Brain Stuff
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