|Why do stars twinkle?
|Question Date: 1999-06-03|
If you were looking from the Space Shuttle in
orbit, you wouldn't see the stars twinkle at all.
What makes the view different from here on earth
is that the light from the stars must pass through
our atmosphere, just as the sun's rays do.
The atmosphere can bend or distort light
traveling through it when it is moving or heated.
You can see this when looking down a long road on
a hot day and the horizon shimmers, or when you
look at something beyond a candle flame.
it's not the stars that twinkle, really, but the
air we look through that makes them appear that
Here's another effect of the
atmosphere you may want to investigate: why is the
Stars appear to twinkle because the light that
they emit is bent back and forth just a little as
it comes through the atmosphere to your eyes.
Your question is a good one. Stars twinkle
because of irregularities in our atmosphere.
Sometimes you hear or read about "crystal nights"
or "nights when the stars were so vivid" and you
might note that these descriptions come from
remote places or places that are well above sea
level. The amount that a star shifts with the
atmosphere will depend on what's in the atmosphere
and how much atmosphere there is between you and
space. Close to sea level, or in polluted areas,
there are a lot of particles in the atmosphere and
the atmosphere is dense. Although hard to see
normally, the atmosphere can be observed and when
you're looking through a lot of atmosphere to see
a star, the smallest perturbations from wind will
make the atmosphere appear to ripple. A very good
example of this is when it is really hot and you
can see objects ripple in the air because of the
differences in air density between you and the
object. If you go to very high altitudes, there
is less atmosphere obstructing your vision so the
effects are less severe and the stars seem
crisper, almost like little crystals.
you think astronomers often like to build
telescopes in remote places and on mountains?
Stars 'twinkle' due to the Earth's atmosphere. A
volume of gas in the atmosphere can delay light
arriving from a distant star compared to light
that did not pass through the gas, and also the
gas can change the direction that the light
travels. (Can substances here on Earth do the
same things to light?) If the atmosphere never
changed, the stars would not seem to twinkle.
However, winds in layers of the atmosphere move
the gasses around and change their densities,
delaying and deflecting light by different
amounts. Light traveling from a distant star will
take different paths over time to reach the Earth,
and due to the different densities of gasses in
these paths, will hit different locations on the
Earth's surface and will have its intensity
changed. So, if you stand in one place, you will
see the star light seem to come and go, or
If you knew where the star light
was going, and could correct for the changing
intensity, could you see stars without them
appearing to twinkle? No human could, because the
atmosphere typically changes the light over 100
times a second, and no human can react that fast.
On the other hand, computers can, and are now
being used to adjust mirror segments in large
telescopes. These 'adaptive optics' systems are
now being installed in many of the world's
Earth-based telescopes. In a few years, we should
start to see much clearer pictures of stars and
galaxies taken from Earth.
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